IEC 60335-2-21:2012

Household and similar electrical appliances - Safety - Part 2-21: Particular requirements for storage water heaters

IEC 60335-2-21:2012 deals with the safety of electric storage water heaters for household and similar purposes and intended for heating water below boiling temperature, their rated voltage being not more than 250 V for single-phase appliances and 480 V for other appliances. Appliances not intended for normal household use but which nevertheless may be a source of danger to the public, such as appliances intended to be used by laymen in shops, in light industry and on farms, are within the scope of this standard. This standard is also applicable to immersion heater units intended to be retrofitted in a heat exchange closed water heater having provision for retrofitting. Such a unit shall comply with the requirements in Annex AA. As far as is practicable, this standard deals with the common hazards presented by appliances that are encountered by all persons in and around the home. However, in general, it does not take into account persons (including children) whose physical, sensory or mental capabilities, or lack of experience and knowledge prevents them from using the appliance safely without supervision or instruction or children playing with the appliance. This sixth edition cancels and replaces the fifth edition published in 2002 including its Amendment 1 (2004) and its Amendment 2 (2008). The principal changes in this edition as compared with the fifth edition of IEC 60335-2-21 are as follows:
- added requirements for immersion heater units (fixed immersion heaters);
- removed reference to ISO 13732-1 from Bibliography. The attention of National Committees is drawn to the fact that equipment manufacturers and testing organizations may need a transitional period following publication of a new, amended or revised IEC publication in which to make products in accordance with the new requirements and to equip themselves for conducting new or revised tests. It is the recommendation of the committee that the content of this publication be adopted for implementation nationally not earlier than 12 months or later than 36 months from the date of publication. Keywords: Storage, Immersion, Water, Heater
This publication is to be read in conjunction with IEC 60335-1:2010. The contents of the corrigendum of April 2013 have been included in this copy.

Appareils électrodomestiques et analogues - Sécurité - Partie 2-21: Règles particulières pour les chauffe-eau à accumulation

La CEI 60335-2-21:2012 traite de la sécurité des chauffe-eau à accumulation pour usages domestiques et analogues destinés à chauffer l'eau à une température inférieure à la température d'ébullition dont la tension assignée n'est pas supérieure à 250 V pour les appareils monophasés et à 480 V pour les autres appareils. Les appareils qui ne sont pas destinés à un usage domestique normal mais qui peuvent néanmoins constituer une source de danger pour le public, tels que les appareils destinés à être utilisés par des usagers non avertis dans des magasins, chez des artisans et dans des fermes, sont compris dans le domaine d'application de la présente norme. La présente norme est également applicable aux éléments thermoplongeurs destinés à être rénovés dans un chauffe-eau fermé à échange thermique prévu pour la remise à niveau. Un tel élément doit être conforme aux exigences de l'Annexe AA. Dans la mesure du possible, la présente norme traite des risques ordinaires présentés par les appareils encourus par tous les individus à l'intérieur et autour de l'habitation. Cependant, cette norme ne tient pas compte en général des personnes (y compris des enfants) dont les capacités physiques, sensorielles ou mentales, ou le manque d'expérience et de connaissance les empêchent d'utiliser l'appareil en toute sécurité sans surveillance ou instruction; de l'utilisation de l'appareil comme jouet par des enfants. Cette sixième édition annule et remplace la cinquième édition parue en 2002, son Amendement 1 (2004) et son Amendement 2 (2008). Par rapport à la cinquième édition de la CEI 60335-2-21, les principales modifications indiquées ci-après ont été apportées dans la présente édition (les modifications mineures ne sont pas mentionnées):
- ajout d'exigences pour les éléments thermoplongeurs (thermoplongeurs fixes);
- retrait de la référence à l'ISO 13732-1 dans la Bibliographie. L'attention des Comités Nationaux est attirée sur le fait que les fabricants d'appareils et les organismes d'essai peuvent avoir besoin d'une période transitoire après la publication d'une nouvelle publication CEI, ou d'une publication amendée ou révisée, pour fabriquer des produits conformes aux nouvelles exigences et pour adapter leurs équipements aux nouveaux essais ou aux essais révisés. Le comité recommande que le contenu de cette publication soit entériné au niveau national au plus tôt 12 mois et au plus tard 36 mois après la date de publication. Mots-clés: thermoplongeurs, chauffe-eau
Cette publication doit être lue conjointement avec la CEI 60335-1:2010. Le contenu du corrigendum d'avril 2013 a été pris en considération dans cet exemplaire.

General Information

• Status: Published
• Publication Date: 05-Nov-2012
• ICS: 13.120 - Domestic safety
• ICS: 91.140.65 - Water heating equipment
• Technical Committee: TC 61 - Safety of household and similar electrical appliances
• Current Stage: DELPUB - Deleted Publication
• Start Date: 18-Oct-2022
• Completion Date: 30-Nov-2021

Relations

• Amended By: IEC 60335-2-21:2012/AMD1:2018 - Amendment 1 - Household and similar electrical appliances - Safety - Part 2-21: Particular requirements for storage water heaters
• Effective Date: 05-Sep-2023
• Corrected By: IEC 60335-2-21:2012/COR1:2013 - Corrigendum 1 - Household and similar electrical appliances - Safety - Part 2-21: Particular requirements for storage water heaters
• Effective Date: 05-Sep-2023
• Revises: IEC 60335-2-21:2002/AMD1:2004 - Amendment 1 - Household and similar electrical appliances - Safety - Part 2-21: Particular requirements for storage water heaters
• Effective Date: 05-Sep-2023
• Revises: IEC 60335-2-21:2002 - Household and similar electrical appliances - Safety - Part 2-21: Particular requirements for storage water heaters
• Effective Date: 05-Sep-2023
• Revises: IEC 60335-2-21:2002/COR1:2007 - Corrigendum 1 - Household and similar electrical appliances - Safety - Part 2-21: Particular requirements for storage water heaters
• Effective Date: 05-Sep-2023
• Revised: IEC 60335-2-21:2022 - Household and similar electrical appliances - Safety - Part 2-21: Particular requirements for storage water heaters
• Effective Date: 05-Sep-2023
• Revises: IEC 60335-2-21:2002/AMD2:2008 - Amendment 2 - Household and similar electrical appliances - Safety - Part 2-21: Particular requirements for storage water heaters
• Effective Date: 05-Sep-2023

Overview

IEC 60335-2-21:2012 is an international safety standard developed by the International Electrotechnical Commission (IEC) that specifies particular safety requirements for household and similar electric storage water heaters. This standard applies to storage water heaters designed to heat water below boiling temperature, with rated voltages up to 250 V for single-phase appliances and 480 V for other types.

This sixth edition incorporates updates including new provisions for immersion heater units intended for retrofitting in closed heat exchange water heaters. It complements IEC 60335-1:2010, incorporating both the base general safety requirements and this part’s specific provisions for electric storage water heaters. The standard ensures safety against hazards encountered by users during normal household and similar use, including installations in shops, light industry, or farms.

Keywords: Storage water heaters, immersion heaters, electric water heaters, household appliances safety, IEC 60335-2-21.

Key Topics

• Scope and Application
  Focused on electric storage water heaters and immersion heater units for household and similar uses. It also covers appliances that could present dangers to the public outside traditional home environments.

• Safety Requirements
  Detailed technical requirements cover protection against electrical shock, mechanical hazards, overheating, and abnormal operation conditions. These ensure user safety by addressing common risks associated with storage water heaters.

• Testing and Endurance
  The standard defines stringent testing procedures including electrical strength tests, moisture resistance, temperature rise measurement, endurance tests, and overload protection evaluations to verify compliance with safety criteria.

• Marking and Instructions
  Mandates clear marking on appliances, including electrical ratings, warnings, and instructions to facilitate safe installation, operation, and maintenance by users and professionals.

• Immersion Heater Units
  New additional requirements for immersion heater units meant for retrofitting existing closed water heaters, ensuring they meet safety and performance standards.

• Construction and Components
  Specifies construction criteria such as internal wiring, insulation, protection against access to live parts, and robust mechanical strength to withstand operational and environmental stress.

• Conformance and Certification
  Recommends a transition period of 12 to 36 months for manufacturers and testing bodies to align with updated regulations and conduct necessary conformity assessments.

Applications

• Household Water Heating
  Ensures safe design and usage of electric storage water heaters for domestic hot water supply, reducing risks like electrical faults, overheating, and mechanical failures.

• Commercial and Agricultural Settings
  Applied to water heating appliances used by consumers in light industry, farms, and retail environments where laymen operate the equipment.

• Retrofitting Existing Systems
  Provides specific standards for immersion heater units retrofitted in heat exchange closed water heaters, improving safety in upgrading older installations.

• Product Development and Compliance
  Guides manufacturers and engineers in designing and testing safe storage water heaters, enabling global market access through compliance with recognized IEC safety standards.

• Safety Testing Laboratories
  Enables testing organizations to develop adequate test protocols based on internationally accepted criteria for assessing electrical and mechanical safety of water heaters.

Related Standards

• IEC 60335-1:2010
  The general safety requirements standard for household and similar electrical appliances; IEC 60335-2-21 is intended to be used in conjunction with this core document.

• IEC 60335 Series
  Covers safety requirements for various household electrical appliances, ensuring comprehensive safety across multiple appliance categories.

• ISO 13732-1 (Removed Reference)
  Formerly referenced for temperature limits, this standard is no longer included in the bibliography of the 2018 amendment, indicating updated testing or reference practices.

• National and Regional Variants
  Many countries adopt IEC 60335-2-21 nationally, sometimes with local amendments, providing a harmonized safety framework worldwide.

---

By adhering to IEC 60335-2-21:2012, manufacturers, testing bodies, and users can ensure the highest safety standards for electric storage water heaters, promoting reliable performance and reducing hazards associated with domestic and similar water heating appliances. This standard remains essential for anyone involved in the design, production, installation, or regulatory compliance of these critical household appliances.

Standards Content (Sample)

IEC 60335-2-21 ®
Edition 6.0 2012-11
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Household and similar electrical appliances – Safety –
Part 2-21: Particular requirements for storage water heaters

Appareils électrodomestiques et analogues – Sécurité –
Partie 2-21: Règles particulières pour les chauffe-eau à accumulation

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IEC 60335-2-21 ®
Edition 6.0 2012-11
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Household and similar electrical appliances – Safety –

Part 2-21: Particular requirements for storage water heaters

Appareils électrodomestiques et analogues – Sécurité –

Partie 2-21: Règles particulières pour les chauffe-eau à accumulation

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX U
ICS 13.120; 91.140.65 ISBN 978-2-83220-452-8

– 2 – 60335-2-21 © IEC:2012
CONTENTS
FOREWORD . 4
INTRODUCTION . 7
1 Scope . 8
2 Normative references . 9
3 Terms and definitions . 9
4 General requirement . 10
5 General conditions for the tests . 10
6 Classification . 10
7 Marking and instructions . 10
8 Protection against access to live parts . 12
9 Starting of motor-operated appliances . 12
10 Power input and current. 12
11 Heating. 12
12 Void . 12
13 Leakage current and electric strength at operating temperature . 12
14 Transient overvoltages . 12
15 Moisture resistance . 12
16 Leakage current and electric strength . 12
17 Overload protection of transformers and associated circuits . 13
18 Endurance . 13
19 Abnormal operation . 13
20 Stability and mechanical hazards. 14
21 Mechanical strength . 14
22 Construction . 14
23 Internal wiring . 16
24 Components . 16
25 Supply connection and external flexible cords . 18
26 Terminals for external conductors . 18
27 Provision for earthing . 18
28 Screws and connections . 18
29 Clearances, creepage distances and solid insulation . 18
30 Resistance to heat and fire . 18
31 Resistance to rusting . 19
32 Radiation, toxicity and similar hazards . 19
Annexes . 22
Annex A (informative) Routine tests . 22
Annex R (normative) Software evaluation . 23
Annex AA (normative) Additional requirement for immersion heater units intended for
the installation in heat exchange closed water heaters . 24
Bibliography . 27

60335-2-21 © IEC:2012 – 3 –
Figure 101 – Examples of types of storage water heaters . 20
Figure 102 – Example of positions of the thermocouples . 21

– 4 – 60335-2-21 © IEC:2012
INTERNATIONAL ELECTROTECHNICAL COMMISSION
______________
HOUSEHOLD AND SIMILAR ELECTRICAL APPLIANCES –
SAFETY –
Part 2-21: Particular requirements for storage water heaters

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
This part of International Standard IEC 60335 has been prepared by IEC technical committee
61: Safety of household and similar electrical appliances.
This sixth edition cancels and replaces the fifth edition published in 2002 including its
Amendment 1 (2004) and its Amendment 2 (2008). It constitutes a technical revision.
The principal changes in this edition as compared with the fifth edition of IEC 60335-2-21 are
as follows (minor changes are not listed):
– added requirements for immersion heater units (fixed immersion heaters);
– removed reference to ISO 13732-1 from Bibliography.

60335-2-21 © IEC:2012 – 5 –
The text of this standard is based on the following documents:
FDIS Report on voting
61/4452/FDIS 61/4505/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
This part 2 is to be used in conjunction with the latest edition of IEC 60335-1 and its
amendments. It was established on the basis of the fifth edition (2010) of that standard.
NOTE 1 When “Part 1” is mentioned in this standard, it refers to IEC 60335-1.
This part 2 supplements or modifies the corresponding clauses in IEC 60335-1, so as to
convert that publication into the IEC standard: Safety requirements for storage water heaters.
When a particular subclause of Part 1 is not mentioned in this part 2, that subclause applies
as far as is reasonable. When this standard states “addition”, “modification” or “replacement”,
the relevant text in Part 1 is to be adapted accordingly.
NOTE 2 The following numbering system is used:
– subclauses, tables and figures that are numbered starting from 101 are additional to those in Part 1;
– unless notes are in a new subclause or involve notes in Part 1, they are numbered starting from 101, including
those in a replaced clause or subclause;
– additional annexes are lettered AA, BB, etc.
NOTE 3 The following print types are used:
– requirements: in roman type;
– test specifications: in italic type;
– notes: in small roman type.
Words in bold in the text are defined in Clause 3. When a definition concerns an adjective, the adjective and the
associated noun are also in bold.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
NOTE 4 The attention of National Committees is drawn to the fact that equipment manufacturers and testing
organizations may need a transitional period following publication of a new, amended or revised IEC publication in
which to make products in accordance with the new requirements and to equip themselves for conducting new or
revised tests.
It is the recommendation of the committee that the content of this publication be adopted for implementation
nationally not earlier than 12 months or later than 36 months from the date of publication.
A list of all parts of the IEC 60335 series, under the general title: Household and similar
electrical appliances – Safety, can be found on the IEC website.
The following differences exist in the countries indicated below.
– 6.1: Class 0I appliances are allowed (Japan).

– 6 – 60335-2-21 © IEC:2012
– 6.2: IPX0 water heaters are allowed (France, United Kingdom and USA).
– 7.1: Additional markings are required (Australia, New Zealand and South Africa).
– 7.1: The rated pressure is to be marked in pounds per square inch (USA).
– 7.1: Open outlet water heaters are not required to be marked with rated pressure (USA).
– 7.12.1: Additional instructions are required (South Africa).
– 11.7: The test is different (USA).
– 13.2: An additional leakage current test is required (China).
– 19.1: Appliances incorporating sheathed heating elements are not required to have an
outer enclosure of metal but their rated power input is limited to 12 kW (USA).
– 19.101: The test is different (USA).
– 22.47: The minimum pressure is 2,1 MPa. The test is not carried out on water heaters
having a capacity less than 2 l or on appliances having containers open to the atmosphere
(USA).
– 22.101: Pressure reducing valves have to be designed for an inlet pressure of 2 MPa
(South Africa).
– 22.102: The temperature limit is 95 °C (South Africa).
– 22.102: The temperature limit is 85 °C (USA).
– 22.101: The minimum rated pressure is 1,0 MPa (Denmark, Finland, Norway and Sweden).
– 22.103: Closed water heaters having a capacity exceeding 50 l or a rated power input
exceeding 2 kW have to incorporate a pressure-relief device sensitive to both pressure
and temperature that operates before the water temperature reaches 99 °C (South Africa).
– 22.103: Closed water heaters have to incorporate a temperature relief valve or a combined
temperature and pressure-relief valve that operates before the water temperature reaches
100 °C (United Kingdom).
– 22.106: The thermal cut-out of single-phase closed water heaters need only provide
single-pole disconnection (Japan).
– 22.106: For all closed water heaters, the thermal cut-out is to provide all-pole
disconnection (France, Netherlands,).
– 22.109: A tool is not required for draining the appliance (USA).
– 22.110: Additional requirements apply to plastic or resin-based containers for open outlet,
cistern type and low pressure type (South Africa).
– 24.1.4 Additional requirements apply to Thermal cut-outs (South Africa)
– 24.101: Thermal cut-outs are required to have a trip-free switching mechanism (USA).
– 24.102: The maximum water temperature is 99 °C (Japan, Norway, Portugal, United
Kingdom and USA).
– 24.102: The temperature limit of 130 °C is only allowed for closed water heaters having a
rated pressure of at least 0,4 MPa (South Africa).
The contents of the corrigendum of April 2013 have been included in this copy.

60335-2-21 © IEC:2012 – 7 –
INTRODUCTION
It has been assumed in the drafting of this International Standard that the execution of its
provisions is entrusted to appropriately qualified and experienced persons.
This standard recognizes the internationally accepted level of protection against hazards such
as electrical, mechanical, thermal, fire and radiation of appliances when operated as in
normal use taking into account the manufacturer's instructions. It also covers abnormal
situations that can be expected in practice and takes into account the way in which
electromagnetic phenomena can affect the safe operation of appliances.
This standard takes into account the requirements of IEC 60364 as far as possible so that
there is compatibility with the wiring rules when the appliance is connected to the supply
mains. However, national wiring rules may differ.
If an appliance within the scope of this standard also incorporates functions that are covered
by another part 2 of IEC 60335, the relevant part 2 is applied to each function separately, as
far as is reasonable. If applicable, the influence of one function on the other is taken into
account.
When a part 2 standard does not include additional requirements to cover hazards dealt with
in Part 1, Part 1 applies.
NOTE 1 This means that the technical committees responsible for the part 2 standards have determined that it is
not necessary to specify particular requirements for the appliance in question over and above the general
requirements.
This standard is a product family standard dealing with the safety of appliances and takes
precedence over horizontal and generic standards covering the same subject.
NOTE 2 Horizontal and generic standards covering a hazard are not applicable since they have been taken into
consideration when developing the general and particular requirements for the IEC 60335 series of standards. For
example, in the case of temperature requirements for surfaces on many appliances, generic standards, such as
ISO 13732-1 for hot surfaces, are not applicable in addition to Part 1 or part 2 standards.
An appliance that complies with the text of this standard will not necessarily be considered to
comply with the safety principles of the standard if, when examined and tested, it is found to
have other features that impair the level of safety covered by these requirements.
An appliance employing materials or having forms of construction differing from those detailed
in the requirements of this standard may be examined and tested according to the intent of
the requirements and, if found to be substantially equivalent, may be considered to comply
with the standard.
– 8 – 60335-2-21 © IEC:2012
HOUSEHOLD AND SIMILAR ELECTRICAL APPLIANCES –
SAFETY –
Part 2-21: Particular requirements for storage water heaters

1 Scope
This clause of Part 1 is replaced by the following.
This International Standard deals with the safety of electric storage water heaters for
household and similar purposes and intended for heating water below boiling temperature,
their rated voltage being not more than 250 V for single-phase appliances and 480 V for
other appliances.
Appliances not intended for normal household use but which nevertheless may be a source of
danger to the public, such as appliances intended to be used by laymen in shops, in light
industry and on farms, are within the scope of this standard.
This standard is also applicable to immersion heater units intended to be retrofitted in a
heat exchange closed water heater having provision for retrofitting. Such a unit shall comply
with the requirements in Annex AA.
NOTE Australia, Netherlands and New Zealand do not allow immersion heater units intended to be retrofitted in
a heat exchange closed water heater unless:
– the immersion heater unit has been tested with the tank models and brands listed in the instructions of the
immersion heater unit;
– the tank models and brands list the models of the immersion heater units that can be retrofitted.
As far as is practicable, this standard deals with the common hazards presented by
appliances that are encountered by all persons in and around the home. However, in general,
it does not take into account
– persons (including children) whose
• physical, sensory or mental capabilities, or
• lack of experience and knowledge
prevents them from using the appliance safely without supervision or instruction;
– children playing with the appliance.
NOTE 101 Attention is drawn to the fact that
– for appliances intended to be used in vehicles or on board ships or aircraft, additional requirements may be
necessary;
– in many countries additional requirements are specified by the national health authorities, the national
authorities responsible for the protection of labour and similar authorities;
– in many countries regulations exist for the installation of equipment connected to the water mains.
NOTE 102 This standard does not apply to
– appliances for boiling water (IEC 60335-2-15);
– instantaneous water heaters (IEC 60335-2-35);
– commercial dispensing appliances and vending machines (IEC 60335-2-75);
– appliances intended exclusively for industrial purposes;
– appliances intended to be used in locations where special conditions prevail, such as the presence of a
corrosive or explosive atmosphere (dust, vapour or gas).

60335-2-21 © IEC:2012 – 9 –
2 Normative references
This clause of Part 1 is applicable.
3 Terms and definitions
This clause of Part 1 is applicable except as follows.
3.1.9 Replacement:
normal operation
operation of the appliance after installation in accordance with the instructions and filled with
cold water
3.101
storage water heater
stationary appliance for heating and storing water in a container and incorporating devices
to control the water temperature
3.102
closed water heater
unvented storage water heater intended to operate at the pressure of the water system, the
flow of water being controlled by one or more valves in the outlet system
Note 1 to entry: A closed water heater is shown in Figure 101a.
Note 2 to entry: The operating pressure may be the output pressure of a reducing or boosting device.
3.103
cistern-fed water heater
storage water heater that is vented to atmosphere and intended to be supplied by water
under gravity from a separate cistern, the flow of water being controlled by one or more
valves in the outlet system
Note 1 to entry: A cistern-fed water heater is shown in Figure 101d.
Note 2 to entry: The water heater may be installed so that the expanded water returns to the cistern.
Note 3 to entry: In a cistern-fed water heater, the pressure in the container results from the column of water in
the cistern.
3.104
cistern-type water heater
storage water heater having a container supplied by water under gravity from a cistern
incorporated in the appliance.
Note 1 to entry: The expanded water can return to the cistern, the flow of water being controlled by one or more
valves in the outlet system
Note 2 to entry: A cistern-type water heater is shown in Figure 101c.
Note 3 to entry: In a cistern-type water heater, the surface of the water is always at atmospheric pressure.
3.105
open-outlet water heater
storage water heater in which the flow of water is only controlled by a valve in the inlet pipe
and in which the expanded or displaced water flows through the outlet
Note 1 to entry: An open-outlet water heater is shown in Figure 101b.
Note 2 to entry: In an open-outlet water heater, the static pressure at the outlet is always at atmospheric
pressure.
– 10 – 60335-2-21 © IEC:2012
3.106
low-pressure water heater
storage water heater that is vented to atmosphere and intended to be connected to the water
mains through a pressure reducing valve, the flow of water being controlled by one or more
valves in the outlet system
Note 1 to entry: A low-pressure water heater is shown in Figure 101e.
3.107
rated pressure
water pressure assigned to the appliance by the manufacturer
3.108
heat exchange water heater
storage water heater in which heated water is fed into a heat exchanger, such as a coiled
tube or similar device, which is itself immersed in a container with the water to be heated.
Note 1 to entry: The heated water fed into the heat exchanger is heated from a primary heat source such as a
solar panel or heat pump.
Note 2 to entry: A heat exchange water heater is shown in Figure 101f.
4 General requirement
This clause of Part 1 is applicable.
5 General conditions for the tests
This clause of Part 1 is applicable except as follows.
5.2 Addition:
NOTE 101 Additional appliances can be required if damage occurs during the tests of 19.2 or 19.3.
5.3 Addition:
When the tests are carried out on a single appliance, the tests of 22.47, 22.102, 22.103, and
24.102 are carried out before the tests of Clause 19.
6 Classification
This clause of Part 1 is applicable except as follows.
6.1 Modification:
Water heaters shall be class I, class II or class III.
6.2 Addition:
Water heaters for installation outdoors shall be at least IPX4. Other water heaters shall be at
least IPX1.
7 Marking and instructions
This clause of Part 1 is applicable except as follows.

60335-2-21 © IEC:2012 – 11 –
7.1 Addition:
Appliances, other than cistern-type water heaters, shall be marked with the rated pressure
in pascals.
Appliances shall be marked with the rated capacity in litres.
Closed water heaters shall be marked with a statement that a pressure-relief device is to be
fitted in the installation, unless it is incorporated in the appliance.
Closed water heaters having a rated pressure less than 0,6 MPa and low-pressure water
heaters shall be marked with a statement that a pressure reducing valve is to be fitted in the
installation.
Open-outlet water heaters shall be marked, close to the outlet connection or on a tag
attached to the appliance, with the substance of the following:
WARNING: This outlet acts as a vent and must only be connected to a fitting
recommended by the manufacturer. It must not be connected to a tap.
7.12 Addition:
The instructions for closed water heaters shall state the substance of the following:
– the water may drip from the discharge pipe of the pressure-relief device and that this pipe
must be left open to the atmosphere;
– the pressure-relief device is to be operated regularly to remove lime deposits and to verify
that it is not blocked;
– how the water heater can be drained.
7.12.1 Addition:
The installation instructions shall state the substance of the following:
– the type or characteristics of the pressure-relief device and how to connect it, unless it is
incorporated in the appliance;
– a discharge pipe connected to the pressure-relief device is to be installed in a
continuously downward direction and in a frost-free environment;
– the type or characteristics of a pressure reducing valve and the installation details (for
appliances having a rated pressure less than 0,6 MPa).
The instructions for closed water heaters incorporating a heat exchanger shall give details
on the installation of control devices and the temperature settings that are necessary to
prevent operation of the thermal cut-out caused by the heat from the exchanger.
The instructions for cistern-fed water heaters and low-pressure water heaters shall contain
the substance of the following:
WARNING: Do not connect any pressure-relief device to the vent pipe of this water
heater.
7.101 The water inlet and the water outlet shall be identified. This identification shall not be
on detachable parts. If colours are used, blue shall be used for the inlet and red for the
outlet. An alternative means of identification may be by means of arrows showing the
direction of the water flow.
Compliance is checked by inspection.

– 12 – 60335-2-21 © IEC:2012
8 Protection against access to live parts
This clause of Part 1 is applicable.
9 Starting of motor-operated appliances
This clause of Part 1 is not applicable.
10 Power input and current
This clause of Part 1 is applicable.
11 Heating
This clause of Part 1 is applicable except as follows.
11.7 Replacement:
The appliance is operated until steady conditions are established or until the thermostat
interrupts the current for the first time after 16 h, whichever is shorter.
12 Void
13 Leakage current and electric strength at operating temperature
This clause of Part 1 is applicable.
14 Transient overvoltages
This clause of Part 1 is applicable.
15 Moisture resistance
This clause of Part 1 is applicable except as follows.
15.2 Addition:
The test is only applicable to cistern-type water heaters.
15.3 Addition:
NOTE 101 If the appliance is too large for the humidity cabinet, the test can be carried out on those parts that
contain electrical components.
16 Leakage current and electric strength
This clause of Part 1 is applicable.

60335-2-21 © IEC:2012 – 13 –
17 Overload protection of transformers and associated circuits
This clause of Part 1 is applicable.
18 Endurance
This clause of Part 1 is not applicable.
19 Abnormal operation
This clause of Part 1 is applicable except as follows.
19.1 Modification:
Instead of the tests specified for appliances incorporating heating elements, the following
applies.
For closed water heaters, low-pressure water heaters and open-outlet water heaters,
compliance is checked by the tests of 19.2, 19.3 and 19.4 if applicable. However, 19.101
applies instead for appliances not liable to be emptied in normal use and having all four of the
following features:
– an outer enclosure of metal or a water container of metal and an outer enclosure of non-
metallic material;
NOTE 101 Non-metallic covers can be used for the supply terminals and controls.
– non-combustible thermal insulation;
NOTE 102 Insulation withstanding the needle flame test of Annex E is considered to be non-combustible.
– a capacity exceeding 30 l;
– a rated power input not exceeding 6 kW.
NOTE 103 Appliances are not considered liable to be emptied in normal use if emptying through the inlet is
prevented by a check valve, a pipe interrupter or an air gap. These devices can be fitted in the inlet pipe in
accordance with the instructions. Emptying through openings provided for servicing purposes only is not
considered to be normal use.
NOTE 104 Cistern-fed water heaters and cistern-type water heaters are not subjected to the tests.
19.2 Addition:
The appliance is operated empty, any thermal control that operates during the test of
Clause 11 being short-circuited.
NOTE 101 If the appliance is provided with more than one thermal control, these are short-circuited in turn.
19.3 Addition:
NOTE 101 If the water heater has been damaged during the previous test, a new appliance is used.
19.4 Replacement:
For open-outlet water heaters, the test of 19.2 is repeated but with the container filled with
water to a level at least 10 mm above the highest point of the heating element. The appliance
is operated at 1,15 times rated power input under normal operation.
NOTE 101 If the water heater has been damaged during previous tests, a new appliance is used.

– 14 – 60335-2-21 © IEC:2012
19.13 Addition:
There shall be no leakage from the container during the tests.
19.101 The appliance is tested for 24 h under the conditions specified in Clause 11 but with
the container empty.
20 Stability and mechanical hazards
This clause of Part 1 is applicable.
21 Mechanical strength
This clause of Part 1 is applicable.
22 Construction
This clause of Part 1 is applicable except as follows.
22.6 Addition:
The enclosure shall have a drain hole positioned so that the water can drain without impairing
electrical insulation, unless condensed water cannot accumulate within the enclosure in
normal use. The hole shall be at least 5 mm in diameter or 20 mm in area with a width of at
least 3 mm.
Compliance is checked by inspection and measurement.
22.20 Addition:
Thermal insulation shall not be used for basic insulation of internal wiring.
22.47 Replacement:
Appliances shall withstand the water pressure occurring in normal use.
Compliance is checked by subjecting the appliance to a water pressure of
– twice the rated pressure, for closed water heaters. If the water heater is supplied
through a pressure reducing valve, the container is subjected to twice the working pressure
instead;
NOTE 1 The pressure reducing valve can be incorporated in the water-inlet pipe.
NOTE 2 The working pressure is the maximum pressure in the container measured during the test of Clause 11.
– 1,5 times rated pressure, for cistern-fed water heaters and low-pressure water
heaters;
– 0,15 MPa, for open-outlet water heaters;
– 0,03 MPa, for cistern-type water heaters.
Pressure-relief devices are rendered inoperative. The pressure is raised at a rate of
0,13 MPa/s to the specified value and is maintained at that value for 15 min.

60335-2-21 © IEC:2012 – 15 –
Water shall not leak from the appliance and there shall be no permanent deformation to such
an extent that compliance with this standard is impaired.
NOTE 3 Heat exchangers incorporated in an appliance are subjected to a pressure test based on their working
pressure.
NOTE 4 Damage to a protective coating on the inside of containers is not considered to be a hazard.
22.101 The rated pressure of closed water heaters intended for direct connection to the
water main shall be at least 0,6 MPa.
The rated pressure of closed water heaters and low-pressure water heaters, intended to
be supplied by a pressure reducing valve that is not incorporated in the appliance, shall be at
least 0,1 MPa.
The rated pressure of cistern-fed water heaters shall not exceed 0,2 MPa.
NOTE The rated pressure of open-outlet water heaters is 0 Pa.
Compliance is checked by inspection.
22.102 Closed water heaters shall be constructed so that repeated drawing off does not
cause the water to boil.
Compliance is checked by the following test.
The appliance is operated as specified in Clause 11.
When the thermostat has operated for the first time, water is drawn off at a rate of
approximately 2 l/min or 10 % of the capacity of the appliance per minute, whichever is less,
until the thermostat switches on again.
When the thermostat next operates, water is drawn off again at the same rate until the
thermostat switches on, this sequence being repeated until steady conditions are
established.
The temperature of the water, measured by means of a thermocouple at the outlet, shall not
exceed 98 °C.
22.103 Pressure-relief devices of closed water heaters shall prevent the pressure in the
container from exceeding the rated pressure by more than 0,1 MPa.
Compliance is checked by subjecting the container to a slowly increasing water pressure.
NOTE The pressure-relief device can be fitted during installation.
22.104 The outlet of open-outlet water heaters shall be constructed so that the water flow
is not limited to such an extent that the container is subjected to a significant pressure.
NOTE This requirement is considered to be met if the cross-sectional area of the water outlet is not less than that
of the inlet.
The vent pipe of low pressure water heaters shall have an internal diameter of at least
20 mm.
Compliance is checked by inspection and measurement.
22.105 Cistern-type water heaters shall be constructed so that the container is always at
atmospheric pressure by means of a vent having an area of at least 30 mm and a minimum
dimension of at least 3 mm.
– 16 – 60335-2-21 © IEC:2012
Compliance is checked by inspection and by measurement.
22.106 Closed water heaters shall incorporate a thermal cut-out providing all-pole
disconnection and which operates independently from the thermostat. However, for
appliances intended to be connected to fixed wiring, the neutral conductor need not be
disconnected.
Compliance is checked by inspection.
22.107 Heating elements and thermal control sensors in contact with the outer surface of the
container shall be held in position securely.
Compliance is checked by inspection.
22.108 Appliances for wall mounting shall have reliable provision for fixing to a wall,
independent of the connection to the water mains.
Compliance is checked by inspection.
22.109 Appliances having a capacity of more than 15 l that cannot be emptied through a
drain fitted in the water pipes shall incorporate means for draining that requires a tool for its
operation.
Compliance is checked by inspection and by manual test.
NOTE 1 Residual water in the container below the end of the inlet pipe is disregarded.
NOTE 2 The means for draining can be combined with a pressure-relief valve.
22.110 Open-outlet water heaters having plastic containers shall be constructed to ensure
that the appliance is only likely to be installed in the intended orientation.
NOTE Appliances marked with the mounting position adjacent to the water connections are considered to meet
this requirement.
Compliance is checked by inspection.
22.111 Closed water heaters incorporating a heat exchanger shall be constructed so that
during normal use the thermal cut-out does not operate due to heat from the exchanger.
Thermostatic valves, by-pass valves and similar controlling devices used for this purpose
shall be supplied with the appliance.
Compliance is checked by inspection.
23 Internal wiring
This clause of Part 1 is applicable.
24 Components
This clause of Part 1 is applicable except as follows.
24.1.4 Addition:
60335-2-21 © IEC:2012 – 17 –
Thermal cut-outs incorporated in closed water heaters shall comply with the requirements
for Type 2.B controls in Clauses 13, 15, 16 17 and 20 of IEC 60730-1, unless they are tested
with the appliance.
24.101 Thermal cut-outs shall be non-self-resetting. They shall have a trip-free switching
mechanism or be located so that they can only be reset after removal of a non-detachable
cover.
Compliance is checked by inspection.
24.102 The operating temperature of the thermal cut-out of a closed water heater shall
ensure that the water temperature cannot exceed 99 °C or that the thermal cut-out operates
before its temperature exceeds 110 °C.
Compliance is checked by the test of 24.102.1 for water temperatures not exceeding 99 °C or
by the test of 24.102.2 for thermal cut-outs having an operating temperature up to 110 °C.
24.102.1 The appliance is operated under the conditions specified in Clause 11 until the
thermostat operates for the first time. A quantity of water equal to 25 % of the capacity of the
container is then drawn off so that it is replaced by cold water.
Immediately after the thermostat operates for the second time, it is short-circuited. The test
is continued until the thermal cut-out operates. The outlet valve is then opened and the
temperature of the water measured at the outlet.
The temperature shall not exceed 99 °C.
If compliance relies on the operation of an electronic circuit, the test is repeated under the
following conditions applied separately:
– the fault conditions in a) to g) of 19.11.2 applied one at a time to the ele
...

IEC 60335-2-21 ®
Edition 6.1 2018-08
CONSOLIDATED VERSION
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Household and similar electrical appliances – Safety –
Part 2-21: Particular requirements for storage water heaters

Appareils électrodomestiques et analogues – Sécurité –
Partie 2-21: Règles particulières pour les chauffe-eau à accumulation

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IEC 60335-2-21 ®
Edition 6.1 2018-08
CONSOLIDATED VERSION
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Household and similar electrical appliances – Safety –

Part 2-21: Particular requirements for storage water heaters

Appareils électrodomestiques et analogues – Sécurité –

Partie 2-21: Règles particulières pour les chauffe-eau à accumulation

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 13.120; 91.140.65 ISBN 978-2-8322-5992-4

IEC 60335-2-21 ®
Edition 6.1 2018-08
CONSOLIDATED VERSION
REDLINE VERSION
VERSION REDLINE
colour
inside
Household and similar electrical appliances – Safety –
Part 2-21: Particular requirements for storage water heaters

Appareils électrodomestiques et analogues – Sécurité –
Partie 2-21: Règles particulières pour les chauffe-eau à accumulation

– 2 – IEC 60335-2-21:2012+AMD1:2018 CSV

© IEC 2018
CONTENTS
FOREWORD . 4

INTRODUCTION . 7

1 Scope . 8

2 Normative references . 9

3 Terms and definitions . 9

4 General requirement . 10

5 General conditions for the tests . 10
6 Classification . 10
7 Marking and instructions . 11
8 Protection against access to live parts . 12
9 Starting of motor-operated appliances . 12
10 Power input and current . 12
11 Heating . 12
12 Void . 13
13 Leakage current and electric strength at operating temperature . 13
14 Transient overvoltages . 13
15 Moisture resistance . 13
16 Leakage current and electric strength . 13
17 Overload protection of transformers and associated circuits . 13
18 Endurance . 14
19 Abnormal operation . 14
20 Stability and mechanical hazards . 15
21 Mechanical strength . 15
22 Construction . 15
23 Internal wiring . 17
24 Components . 17
25 Supply connection and external flexible cords . 19
26 Terminals for external conductors . 19
27 Provision for earthing . 19

28 Screws and connections . 19
29 Clearances, creepage distances and solid insulation . 19
30 Resistance to heat and fire . 19
31 Resistance to rusting . 20
32 Radiation, toxicity and similar hazards . 20
Annexes . 23
Annex A (informative) Routine tests . 23
Annex R (normative) Software evaluation . 24
Annex AA (normative) Additional requirement for immersion heater units intended for
the installation in heat exchange closed water heaters . 25
Bibliography . 28

© IEC 2018
Figure 101 – Examples of types of storage water heaters . 21

Figure 102 – Example of positions of the thermocouples . 22

Figure 103 – Probe for measuring surface temperatures . 22

Table 101 – Maximum temperature rises of external accessible surfaces under normal
operating conditions . 13

– 4 – IEC 60335-2-21:2012+AMD1:2018 CSV

© IEC 2018
INTERNATIONAL ELECTROTECHNICAL COMMISSION

______________
HOUSEHOLD AND SIMILAR ELECTRICAL APPLIANCES –

SAFETY –
Part 2-21: Particular requirements for storage water heaters

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
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patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
This consolidated version of the official IEC Standard and its amendment has been prepared
for user convenience.
IEC 60335-2-21 edition 1.1 contains the first edition (2012-11) [documents 61/4452/FDIS and
61/4505/RVD] and its corrigendum (2013-04), and its amendment 1 (2018-08) [documents
61/5563/CDV and 61/5650A/RVC].
In this Redline version, a vertical line in the margin shows where the technical
content is modified by amendment 1. Additions are in green text, deletions are in
strikethrough red text. A separate Final version with all changes accepted is
available in this publication.

© IEC 2018
This part of International Standard IEC 60335 has been prepared by IEC technical committee

61: Safety of household and similar electrical appliances.

This sixth edition constitutes a technical revision.

The principal changes in this edition as compared with the fifth edition of IEC 60335-2-21 are

as follows (minor changes are not listed):

– added requirements for immersion heater units (fixed immersion heaters);

– removed reference to ISO 13732-1 from Bibliography.

This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
This part 2 is to be used in conjunction with the latest edition of IEC 60335-1 and its
amendments. It was established on the basis of the fifth edition (2010) of that standard.
NOTE 1 When “Part 1” is mentioned in this standard, it refers to IEC 60335-1.
This part 2 supplements or modifies the corresponding clauses in IEC 60335-1, so as to
convert that publication into the IEC standard: Safety requirements for storage water heaters.
When a particular subclause of Part 1 is not mentioned in this part 2, that subclause applies
as far as is reasonable. When this standard states “addition”, “modification” or “replacement”,
the relevant text in Part 1 is to be adapted accordingly.
NOTE 2 The following numbering system is used:
– subclauses, tables and figures that are numbered starting from 101 are additional to those in Part 1;
– unless notes are in a new subclause or involve notes in Part 1, they are numbered starting from 101, including
those in a replaced clause or subclause;
– additional annexes are lettered AA, BB, etc.
NOTE 3 The following print types are used:
– requirements: in roman type;
– test specifications: in italic type;
– notes: in small roman type.
Words in bold in the text are defined in Clause 3. When a definition concerns an adjective, the adjective and the
associated noun are also in bold.
The committee has decided that the contents of the base publication and its amendment will
remain unchanged until the stability date indicated on the IEC web site under
"http://webstore.iec.ch" in the data related to the specific publication. At this date, the

publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
NOTE 4 The attention of National Committees is drawn to the fact that equipment manufacturers and testing
organizations may need a transitional period following publication of a new, amended or revised IEC publication in
which to make products in accordance with the new requirements and to equip themselves for conducting new or
revised tests.
It is the recommendation of the committee that the content of this publication be adopted for implementation
nationally not earlier than 12 months or later than 36 months from the date of publication.
A list of all parts of the IEC 60335 series, under the general title: Household and similar
electrical appliances – Safety, can be found on the IEC website.

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© IEC 2018
The following differences exist in the countries indicated below.

– 6.1: Class 0I appliances are allowed (Japan).

– 6.2: IPX0 water heaters are allowed (France, United Kingdom and USA).

– 7.1: Additional markings are required (Australia, New Zealand and South Africa).

– 7.1: The rated pressure is to be marked in pounds per square inch (USA).

– 7.1: Open outlet water heaters are not required to be marked with rated pressure (USA).

– 7.12.1: Additional instructions are required (South Africa).

– 11.7: The test is different (USA).

– 13.2: An additional leakage current test is required (China).
– 19.1: Appliances incorporating sheathed heating elements are not required to have an
outer enclosure of metal but their rated power input is limited to 12 kW (USA).
– 19.101: The test is different (USA).
– 22.47: The minimum pressure is 2,1 MPa. The test is not carried out on water heaters
having a capacity less than 2 l or on appliances having containers open to the atmosphere
(USA).
– 22.101: Pressure reducing valves have to be designed for an inlet pressure of 2 MPa
(South Africa).
– 22.102: The temperature limit is 95 °C (South Africa).
– 22.102: The temperature limit is 85 °C (USA).
– 22.101: The minimum rated pressure is 1,0 MPa (Denmark, Finland, Norway and Sweden).
– 22.103: Closed water heaters having a capacity exceeding 50 l or a rated power input
exceeding 2 kW have to incorporate a pressure-relief device sensitive to both pressure
and temperature that operates before the water temperature reaches 99 °C (South Africa).
– 22.103: Closed water heaters have to incorporate a temperature relief valve or a combined
temperature and pressure-relief valve that operates before the water temperature reaches
100 °C (United Kingdom).
– 22.106: The thermal cut-out of single-phase closed water heaters need only provide
single-pole disconnection (Japan).
– 22.106: For all closed water heaters, the thermal cut-out is to provide all-pole
disconnection (France, Netherlands,).
– 22.109: A tool is not required for draining the appliance (USA).
– 22.110: Additional requirements apply to plastic or resin-based containers for open outlet,
cistern type and low pressure type (South Africa).
– 24.1.4 Additional requirements apply to Thermal cut-outs (South Africa)

– 24.101: Thermal cut-outs are required to have a trip-free switching mechanism (USA).
– 24.102: The maximum water temperature is 99 °C (Japan, Norway, Portugal, United
Kingdom and USA).
– 24.102: The temperature limit of 130 °C is only allowed for closed water heaters having a
rated pressure of at least 0,4 MPa (South Africa).

IMPORTANT – The “colour inside” logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct understanding
of its contents. Users should therefore print this publication using a colour printer.

© IEC 2018
INTRODUCTION
It has been assumed in the drafting of this International Standard that the execution of its

provisions is entrusted to appropriately qualified and experienced persons.

This standard recognizes the internationally accepted level of protection against hazards such

as electrical, mechanical, thermal, fire and radiation of appliances when operated as in

normal use taking into account the manufacturer's instructions. It also covers abnormal

situations that can be expected in practice and takes into account the way in which

electromagnetic phenomena can affect the safe operation of appliances.

This standard takes into account the requirements of IEC 60364 as far as possible so that
there is compatibility with the wiring rules when the appliance is connected to the supply
mains. However, national wiring rules may differ.
If an appliance within the scope of this standard also incorporates functions that are covered
by another part 2 of IEC 60335, the relevant part 2 is applied to each function separately, as
far as is reasonable. If applicable, the influence of one function on the other is taken into
account.
When a part 2 standard does not include additional requirements to cover hazards dealt with
in Part 1, Part 1 applies.
NOTE 1 This means that the technical committees responsible for the part 2 standards have determined that it is
not necessary to specify particular requirements for the appliance in question over and above the general
requirements.
This standard is a product family standard dealing with the safety of appliances and takes
precedence over horizontal and generic standards covering the same subject.
NOTE 2 Horizontal and generic standards covering a hazard are not applicable since they have been taken into
consideration when developing the general and particular requirements for the IEC 60335 series of standards. For
example, in the case of temperature requirements for surfaces on many appliances, generic standards, such as
ISO 13732-1 for hot surfaces, are not applicable in addition to Part 1 or part 2 standards.
An appliance that complies with the text of this standard will not necessarily be considered to
comply with the safety principles of the standard if, when examined and tested, it is found to
have other features that impair the level of safety covered by these requirements.
An appliance employing materials or having forms of construction differing from those detailed
in the requirements of this standard may be examined and tested according to the intent of
the requirements and, if found to be substantially equivalent, may be considered to comply
with the standard.
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© IEC 2018
HOUSEHOLD AND SIMILAR ELECTRICAL APPLIANCES –

SAFETY –
Part 2-21: Particular requirements for storage water heaters

1 Scope
This clause of Part 1 is replaced by the following.
This International Standard deals with the safety of electric storage water heaters for
household and similar purposes and intended for heating water below boiling temperature,
their rated voltage being not more than 250 V for single-phase appliances and 480 V for
other appliances.
Appliances not intended for normal household use but which nevertheless may be a source of
danger to the public, such as appliances intended to be used by laymen in shops, in light
industry and on farms, are within the scope of this standard.
This standard is also applicable to immersion heater units intended to be retrofitted in a
heat exchange closed water heater having provision for retrofitting. Such a unit shall comply
with the requirements in Annex AA.
NOTE Australia, Netherlands and New Zealand do not allow immersion heater units intended to be retrofitted in
a heat exchange closed water heater unless:
– the immersion heater unit has been tested with the tank models and brands listed in the instructions of the
immersion heater unit;
– the tank models and brands list the models of the immersion heater units that can be retrofitted.
As far as is practicable, this standard deals with the common hazards presented by
appliances that are encountered by all persons in and around the home. However, in general,
it does not take into account
– persons (including children) whose
• physical, sensory or mental capabilities, or
• lack of experience and knowledge
prevents them from using the appliance safely without supervision or instruction;
– children playing with the appliance.

NOTE 101 Attention is drawn to the fact that
– for appliances intended to be used in vehicles or on board ships or aircraft, additional requirements may be
necessary;
– in many countries additional requirements are specified by the national health authorities, the national
authorities responsible for the protection of labour and similar authorities;
– in many countries regulations exist for the installation of equipment connected to the water mains.
NOTE 102 This standard does not apply to
– appliances for boiling water (IEC 60335-2-15);
– instantaneous water heaters (IEC 60335-2-35);
– commercial dispensing appliances and vending machines (IEC 60335-2-75);
– appliances intended exclusively for industrial purposes;
– appliances intended to be used in locations where special conditions prevail, such as the presence of a
corrosive or explosive atmosphere (dust, vapour or gas).

© IEC 2018
2 Normative references
This clause of Part 1 is applicable except as follows:

Addition:
IEC 60584-1:2013, Thermocouples – Part 1: EMF specifications and tolerances

3 Terms and definitions
This clause of Part 1 is applicable except as follows.
3.1.9 Replacement:
normal operation
operation of the appliance after installation in accordance with the instructions and filled with
cold water
3.101
storage water heater
stationary appliance for heating and storing water in a container and incorporating devices
to control the water temperature
3.102
closed water heater
unvented storage water heater intended to operate at the pressure of the water system, the
flow of water being controlled by one or more valves in the outlet system
Note 1 to entry: A closed water heater is shown in Figure 101a.
Note 2 to entry: The operating pressure may be the output pressure of a reducing or boosting device.
3.103
cistern-fed water heater
storage water heater that is vented to atmosphere and intended to be supplied by water
under gravity from a separate cistern, the flow of water being controlled by one or more
valves in the outlet system
Note 1 to entry: A cistern-fed water heater is shown in Figure 101d.
Note 2 to entry: The water heater may be installed so that the expanded water returns to the cistern.
Note 3 to entry: In a cistern-fed water heater, the pressure in the container results from the column of water in
the cistern.
3.104
cistern-type water heater
storage water heater having a container supplied by water under gravity from a cistern
incorporated in the appliance.
Note 1 to entry: The expanded water can return to the cistern, the flow of water being controlled by one or more
valves in the outlet system
Note 2 to entry: A cistern-type water heater is shown in Figure 101c.
Note 3 to entry: In a cistern-type water heater, the surface of the water is always at atmospheric pressure.
3.105
open-outlet water heater
storage water heater in which the flow of water is only controlled by a valve in the inlet pipe
and in which the expanded or displaced water flows through the outlet

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© IEC 2018
Note 1 to entry: An open-outlet water heater is shown in Figure 101b.

Note 2 to entry: In an open-outlet water heater, the static pressure at the outlet is always at atmospheric
pressure.
3.106
low-pressure water heater
storage water heater that is vented to atmosphere and intended to be connected to the water

mains through a pressure reducing valve, the flow of water being controlled by one or more

valves in the outlet system
Note 1 to entry: A low-pressure water heater is shown in Figure 101e.

3.107
rated pressure
water pressure assigned to the appliance by the manufacturer
3.108
heat exchange water heater
storage water heater in which heated water is fed into a heat exchanger, such as a coiled
tube or similar device, which is itself immersed in a container with the water to be heated.
Note 1 to entry: The heated water fed into the heat exchanger is heated from a primary heat source such as a
solar panel or heat pump.
Note 2 to entry: A heat exchange water heater is shown in Figure 101f.
4 General requirement
This clause of Part 1 is applicable.
5 General conditions for the tests
This clause of Part 1 is applicable except as follows.
5.2 Addition:
NOTE 101 Additional appliances can be required if damage occurs during the tests of 19.2 or 19.3.
5.3 Addition:
When the tests are carried out on a single appliance, the tests of 22.47, 22.102, 22.103, and
24.102 are carried out before the tests of Clause 19.
6 Classification
This clause of Part 1 is applicable except as follows.
6.1 Modification:
Water heaters shall be class I, class II or class III.
6.2 Addition:
Water heaters for installation outdoors shall be at least IPX4. Other water heaters shall be at
least IPX1.
© IEC 2018
7 Marking and instructions
This clause of Part 1 is applicable except as follows.

7.1 Addition:
Appliances, other than cistern-type water heaters, shall be marked with the rated pressure

in pascals.
Appliances shall be marked with the rated capacity in litres.

Closed water heaters shall be marked with a statement that a pressure-relief device is to be
fitted in the installation, unless it is incorporated in the appliance.
Closed water heaters having a rated pressure less than 0,6 MPa and low-pressure water
heaters shall be marked with a statement that a pressure reducing valve is to be fitted in the
installation.
Open-outlet water heaters shall be marked, close to the outlet connection or on a tag
attached to the appliance, with the substance of the following:
WARNING: This outlet acts as a vent and must only be connected to a fitting
recommended by the manufacturer. It must not be connected to a tap.
7.12 Addition:
The instructions for closed water heaters shall state the substance of the following:
– the water may drip from the discharge pipe of the pressure-relief device and that this pipe
must be left open to the atmosphere;
– the pressure-relief device is to be operated regularly to remove lime deposits and to verify
that it is not blocked;
– how the water heater can be drained.
7.12.1 Addition:
The installation instructions shall state the substance of the following:
– the type or characteristics of the pressure-relief device and how to connect it, unless it is
incorporated in the appliance;
– a discharge pipe connected to the pressure-relief device is to be installed in a

continuously downward direction and in a frost-free environment;
– the type or characteristics of a pressure reducing valve and the installation details (for
appliances having a rated pressure less than 0,6 MPa).
The instructions for closed water heaters incorporating a heat exchanger shall give details
on the installation of control devices and the temperature settings that are necessary to
prevent operation of the thermal cut-out caused by the heat from the exchanger.
The instructions for cistern-fed water heaters and low-pressure water heaters shall contain
the substance of the following:
WARNING: Do not connect any pressure-relief device to the vent pipe of this water
heater.
7.101 The water inlet and the water outlet shall be identified. This identification shall not be
on detachable parts. If colours are used, blue shall be used for the inlet and red for the

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© IEC 2018
outlet. An alternative means of identification may be by means of arrows showing the

direction of the water flow.
Compliance is checked by inspection.

8 Protection against access to live parts

This clause of Part 1 is applicable.

9 Starting of motor-operated appliances

This clause of Part 1 is not applicable.
10 Power input and current
This clause of Part 1 is applicable.
11 Heating
This clause of Part 1 is applicable except as follows.
11.3 Addition:
Where the external accessible surfaces are suitably flat and access permits, then the test
probe of Figure 103 may be used to measure the temperature rises of external accessible
surfaces specified in Table 101. The probe is applied with a force of 4 N ± 1 N to the
surface in such a way that the best possible contact between the probe and the surface is
ensured. The measurement is performed after a contact period of 30 s.
The probe may be held in place using a laboratory stand clamp or similar device. Any
measuring instrument giving the same results as the probe may be used.
11.7 Replacement:
The appliance is operated until steady conditions are established or until the thermostat
interrupts the current for the first time after 16 h, whichever is shorter.

11.8 Modification:
During the test, the temperature rises are monitored continuously and shall not exceed the
values shown in Table 3 and Table 101.

© IEC 2018
Table 101 – Maximum temperature rises of external accessible surfaces

under normal operating conditions

a
Surface Temperature rise
K
Bare metal 42
b
Coated metal 49
Glass and ceramic 56
c,d
Plastic and plastic coating > 0,4 mm 62

a
Temperature rises are not measured on:

– tapping connections, pipes, hoses, plumbing fittings, pressure relief valves and sight gauges;

– appliances intended for installation on the roof;
– surfaces not accessible to the 75 mm diameter probe having a hemispherical end.
b
Metal is considered coated when a coating having a minimum thickness of 90 µm made by enamel or non-
substantially plastic coating is used.
c
The temperature rise limit of plastic also applies for plastic material having a metal finish of thickness less
than 0,1 mm.
d
When the thickness of the plastic coating does not exceed 0,4 mm, the temperature rise limits of the coated
metal or of glass and ceramic material apply.

12 Void
13 Leakage current and electric strength at operating temperature
This clause of Part 1 is applicable.
14 Transient overvoltages
This clause of Part 1 is applicable.
15 Moisture resistance
This clause of Part 1 is applicable except as follows.
15.2 Addition:
The test is only applicable to cistern-type water heaters.

15.3 Addition:
NOTE 101 If the appliance is too large for the humidity cabinet, the test can be carried out on those parts that
contain electrical components.
16 Leakage current and electric strength
This clause of Part 1 is applicable.
17 Overload protection of transformers and associated circuits
This clause of Part 1 is applicable.

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© IEC 2018
18 Endurance
This clause of Part 1 is not applicable.

19 Abnormal operation
This clause of Part 1 is applicable except as follows.

19.1 Modification:
Instead of the tests specified for appliances incorporating heating elements, the following
applies.
For closed water heaters, low-pressure water heaters and open-outlet water heaters,
compliance is checked by the tests of 19.2, 19.3 and 19.4 if applicable. However, 19.101
applies instead for appliances not liable to be emptied in normal use and having all four of the
following features:
– an outer enclosure of metal or a water container of metal and an outer enclosure of non-
metallic material;
NOTE 101 Non-metallic covers can be used for the supply terminals and controls.
– non-combustible thermal insulation;
NOTE 102 Insulation withstanding the needle flame test of Annex E is considered to be non-combustible.
– a capacity exceeding 30 l;
– a rated power input not exceeding 6 kW.
NOTE 103 Appliances are not considered liable to be emptied in normal use if emptying through the inlet is
prevented by a check valve, a pipe interrupter or an air gap. These devices can be fitted in the inlet pipe in
accordance with the instructions. Emptying through openings provided for servicing purposes only is not
considered to be normal use.
NOTE 104 Cistern-fed water heaters and cistern-type water heaters are not subjected to the tests.
19.2 Addition:
The appliance is operated empty, any thermal control that operates during the test of
Clause 11 being short-circuited.
NOTE 101 If the appliance is provided with more than one thermal control, these are short-circuited in turn.

19.3 Addition:
NOTE 101 If the water heater has been damaged during the previous test, a new appliance is used.
19.4 Replacement:
For open-outlet water heaters, the test of 19.2 is repeated but with the container filled with
water to a level at least 10 mm above the highest point of the heating element. The appliance
is operated at 1,15 times rated power input under normal operation.
NOTE 101 If the water heater has been damaged during previous tests, a new appliance is used.
19.13 Addition:
There shall be no leakage from the container during the tests.

© IEC 2018
19.101 The appliance is tested for 24 h under the conditions specified in Clause 11 but with

the container empty.
20 Stability and mechanical hazards

This clause of Part 1 is applicable.

21 Mechanical strength
This clause of Part 1 is applicable.

22 Construction
This clause of Part 1 is applicable except as follows.
22.6 Addition:
The enclosure shall have a drain hole positioned so that the water can drain without impairing
electrical insulation, unless condensed water cannot accumulate within the enclosure in
normal use. The hole shall be at least 5 mm in diameter or 20 mm in area with a width of at
least 3 mm.
Compliance is checked by inspection and measurement.
22.20 Addition:
Thermal insulation shall not be used for basic insulation of internal wiring.
22.47 Replacement:
Appliances shall withstand the water pressure occurring in normal use.
Compliance is checked by subjecting the appliance to a water pressure of
– twice the rated pressure, for closed water heaters. If the water heater is supplied
through a pressure reducing valve, the container is subjected to twice the working pressure
instead;
NOTE 1 The pressure reducing valve can be incorporated in the water-inlet pipe.

NOTE 2 The working pressure is the maximum pressure in the container measured during the test of Clause 11.
– 1,5 times rated pressure, for cistern-fed water heaters and low-pressure water
heaters;
– 0,15 MPa, for open-outlet water heaters;
– 0,03 MPa, for cistern-type water heaters.
Pressure-relief devices are rendered inoperative. The pressure is raised at a rate of
0,13 MPa/s to the specified value and is maintained at that value for 15 min.
Water shall not leak from the appliance and there shall be no permanent deformation to such
an extent that compliance with this standard is impaired.
NOTE 3 Heat exchangers incorporated in an appliance are subjected to a pressure test based on their working
pressure.
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© IEC 2018
NOTE 4 Damage to a protective coating on the inside of containers is not considered to be a hazard.

22.101 The rated pressure of closed water heaters intended for direct connection to the

water main shall be at least 0,6 MPa.

The rated pressure of closed water heaters and low-pressure water heaters, intended to

be supplied by a pressure reducing valve that is not incorporated in the appliance, shall be at
least 0,1 MPa.
The rated pressure of cistern-fed water heaters shall not exceed 0,2 MPa.

NOTE The rated pressure of open-outlet water heaters is 0 Pa.
Compliance is checked by inspection.
22.102 Closed water heaters shall be constructed so that repeated drawing off does not
cause the water to boil.
Compliance is checked by the following test.
The appliance is operated as specified in Clause 11.
When the thermostat has operated for the first time, water is drawn off at a rate of
approximately 2 l/min or 10 % of the capacity of the appliance per minute, whichever
...