SIST-TP IEC/TR 60725:2008

Consideration of reference impedances and public supply network impedances for use in determining disturbance characteristics of electrical equipment having a rated current = < 75 A per phase

This technical report records the information that was available and the factors that were taken into account in arriving at the reference impedances that were formerly incorporated in IEC 60555, but which are now incorporated into some sections of IEC 61000-3.[
]In addition, information is given on the impedances of public supply networks associated with service current capacities >=100 A per phase.

Etude des impédances de référence et des impédances des réseaux publics d'alimentation aux fins de la détermination des caractéristiques de perturbation des équipements électriques utilisant un courant nominal = < 75 A par phase

Ce rapport technique consigne les informations disponibles et les facteurs pris en compte lors du calcul des impédances de référence énoncées dans la CEI 60555, désormais intégrés à certaines sections de la CEI 61000-3.[
]De plus, les informations fournies concernent les impédances des réseaux publics de distribution associés à des courants de service ayant une capacité >=100 A par phase.

Ugotovitve o referenčnih impedancah in impedancah javnega napajalnega omrežja za določanje značilnosti motenj električne opreme z nazivnim faznim tokom do vključno 75 A

General Information

• Status: Withdrawn
• Public Enquiry End Date: 30-Sep-2008
• Publication Date: 01-Oct-2008
• Withdrawal Date: 17-Mar-2025
• ICS: 33.100.10 - Emission
• Technical Committee: EMC - Electromagnetic compatibility
• Current Stage: 9900 - Withdrawal (Adopted Project)
• Start Date: 18-Mar-2025
• Due Date: 10-Apr-2025
• Completion Date: 18-Mar-2025
• Ref Project: IEC/TR 60725 - Consideration of reference impedances and public supply network impedances for use in determining disturbance characteristics of electrical equipment having a rated current = < 75 A per phase

Relations

• Replaces: SIST IEC/TR 60725:1998 - Considerations on reference impedances for use in determining the disturbance characteristics of household appliances and similar electrical equipment
• Effective Date: 01-Nov-2008

Overview

SIST-TP IEC/TR 60725:2008 is an important technical report published by the International Electrotechnical Commission (IEC) focusing on the consideration of reference impedances and public supply network impedances. This document is specifically designed to assist in determining the disturbance characteristics of electrical equipment with a rated current of ≤ 75 A per phase. Originally, reference impedances were defined in IEC 60555 but have since been incorporated into sections of IEC 61000-3 standards. Additionally, the report provides information on supply network impedances related to service current capacities of 100 A or more per phase.

The report plays a critical role in understanding the behavior of electrical equipment under typical supply conditions, enabling compliance with electromagnetic compatibility (EMC) limits, especially regarding harmonic currents, voltage fluctuations, and flicker in public low-voltage supply systems.

Key Topics

• Reference Impedances: The report presents standardized reference impedances that account for typical supply conditions for equipment rated at ≤ 75 A per phase. These impedances are essential for evaluating disturbance characteristics in compliance with IEC 61000-3.

• Supply System Variations: Different supply system configurations worldwide are discussed, including three-phase, four-wire systems (230/400 V), and single-phase three-wire systems. The application varies depending on national practices and consumer connections.

• Public Supply Network Impedances: In addition to reference impedances, the report provides methodologies and typical values of supply impedances for public low-voltage networks, including systems with service capacities ≥ 100 A per phase. This data helps manufacturers and network operators understand real-world electrical network conditions.

• Harmonic Impedance and Disturbance Factors: The document includes discussion on harmonic impedance considerations crucial for evaluating equipment conformity against EMC limits covering voltage fluctuations and flicker.

• Probabilistic Assessment: Reference impedance values are often presented with a 95% probability level, indicating that 95% of supply conditions fall below these impedance values, which supports robust and reliable compliance assessments.

Applications

SIST-TP IEC/TR 60725:2008 has practical applications across a broad range of electrical engineering and manufacturing disciplines:

• Electrical Equipment Design: Manufacturers designing equipment with rated currents ≤ 75 A per phase can use the reference impedances to predict equipment performance and disturbance generation under typical supply conditions.

• EMC Compliance Testing: The standard supports testing laboratories and compliance engineers in evaluating equipment according to EMC regulations such as IEC 61000-3-11 and IEC 61000-3-12, ensuring that equipment meets harmonic current and voltage fluctuation limits.

• Distribution Network Planning: Utilities and network operators can utilize the supply impedance data to assess system performance, predict voltage drop and flicker levels, and facilitate conditional connection approvals of electrical equipment per regulatory frameworks.

• International Standardization: Given the variations in supply system designs internationally (e.g., Europe’s 230/400 V three-phase versus the US 120/240 V single-phase systems), this report aids in harmonizing standards and reference points for disturbance characterizations globally.

Related Standards

SIST-TP IEC/TR 60725:2008 is closely related to several other IEC standards that govern electromagnetic compatibility and power quality:

• IEC 61000-3-3: Defines limits for voltage fluctuations and flicker for equipment rated ≤ 16 A per phase, closely linked to the evaluation methods detailed in SIST-TP IEC/TR 60725:2008.

• IEC 61000-3-11: Addresses limits related to voltage changes and flicker for equipment with rated currents ≤ 75 A per phase, integrating reference impedance concepts adapted from SIST-TP IEC/TR 60725:2008.

• IEC 61000-3-12: Establishes harmonic current limits for equipment connected to public low-voltage systems with input currents between 16 A and 75 A per phase.

These standards collectively provide a comprehensive framework for assessing and managing disturbance characteristics of electrical equipment in low-voltage networks worldwide.

---

Keywords: SIST-TP IEC/TR 60725:2008, reference impedance, public supply network impedance, rated current ≤ 75 A, electrical equipment disturbance, supply impedance, electromagnetic compatibility, IEC 61000-3, voltage fluctuations, harmonic impedance, EMC compliance, low-voltage supply system, public electricity network, power quality standards.

Standards Content (Sample)

SLOVENSKI STANDARD
01-november-2008
1DGRPHãþD
SIST IEC/TR 60725:1998
8JRWRYLWYHRUHIHUHQþQLKLPSHGDQFDKLQLPSHGDQFDKMDYQHJDQDSDMDOQHJDRPUHåMD
]DGRORþDQMH]QDþLOQRVWLPRWHQMHOHNWULþQHRSUHPH]QD]LYQLPID]QLPWRNRPGR
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Consideration of reference impedances and public supply network impedances for use in
determining disturbance characteristics of electrical equipment having a rated current = <
75 A per phase
Etude des impédances de référence et des impédances des réseaux publics
d'alimentation aux fins de la détermination des caractéristiques de perturbation des
équipements électriques utilisant un courant nominal = < 75 A par phase
Ta slovenski standard je istoveten z: IEC/TR 60725
ICS:
33.100.10 Emisija Emission
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

RAPPORT CEI
TECHNIQUE IEC
TR 60725
TECHNICAL
Deuxième édition
REPORT
Second edition
2005-05
Etude des impédances de référence et des
impédances des réseaux publics d'alimentation
aux fins de la détermination des caractéristiques
de perturbation des équipements électriques
utilisant un courant nominal ≤75 A par phase

Consideration of reference impedances and public
supply network impedances for use in determining
disturbance characteristics of electrical equipment
having a rated current ≤75 A per phase
 IEC 2005 Droits de reproduction réservés  Copyright - all rights reserved
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électronique ou mécanique, y compris la photocopie et les photocopying and microfilm, without permission in writing from
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Telephone: [phone] Telefax: [phone] E-mail: [e-mail] Web: www.iec.ch
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Pour prix, voir catalogue en vigueur
For price, see current catalogue

TR 60725  IEC:2005 – 3 –
CONTENTS
FOREWORD.5

1 Scope.9
2 Normative references .9
3 Systems of supply .9
4 Supply impedances .11
5 Reference impedances .17
6 Harmonic impedance.21

Annex A (informative) Methods for determining the maximum modulus values of public
electricity supply low-voltage network impedances relevant to three-phase services of
more than 100 A per phase at 50 Hz.23
Annex B (informative) Methods for determining the maximum modulus values of public
electricity supply low-voltage network impedances relevant to three-phase services of
more than 100 A per phase at 60 Hz.41

Figure A.1 – Model used for determining the impedance of a network line conductor
from a transformer to a three-phase service cut-out .27
Figure A.2 – The three-phase impedance diagram of a typical 500 kVA transformer
and mains cable.29

Table 1 – 1980 International survey of residential consumers’ complex supply
impedances, in ohms, for single-phase connections at 50 Hz.13
Table 2 – Modulus values of supply impedance, in ohms at 50 Hz, relevant to the
connection of three-phase equipment and having a 95 % probability of not being
exceeded.15
Table 3 – Modulus values of supply impedance, in ohms at 50 Hz, relevant to the
connection of single-phase equipment and having a 95 % probably of not being
exceeded.17
Table A.1 – The modulus values of the maximum supply impedance, in ohms, of the
line-conductors of 230/400 V, 50 Hz, public electricity supply networks, relevant to
three-phase services having service capacities of 200 A per phase .35
Table A.2 – The modulus values of the maximum supply impedance, in ohms, of the
line and neutral conductors of 230/400 V, 50 Hz, public electricity supply networks,
relevant to three-phase services having service capacities of 200 A per phase.35

TR 60725  IEC:2005 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
CONSIDERATION OF REFERENCE IMPEDANCES AND PUBLIC SUPPLY
NETWORK IMPEDANCES FOR USE IN DETERMINING DISTURBANCE
CHARACTERISTICS OF ELECTRICAL EQUIPMENT HAVING A RATED
CURRENT ≤ 75A PER PHASE
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
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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
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4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
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between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
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5) IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with an IEC Publication.
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
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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.
The main task of IEC technical committees is to prepare International Standards. However, a
technical committee may propose the publication of a technical report when it has collected
data of a different kind from that which is normally published as an International Standard, for
example "state of the art".
IEC 60725, which is a technical report, has been prepared by subcommittee 77A: Low
frequency phenomena, of IEC technical committee 77: Electromagnetic compatibility.
This second edition cancels and replaces the first edition published in 1981. This second
edition constitutes a technical revision in which the major change is the definition of a method
to assess the 3 phase-impedance value in order to apply more easily IEC 61000-3-11.

TR 60725  IEC:2005 – 7 –
The text of this technical report is based on the following documents:
DTR Report on voting
77A/460/DTR 77A/485/RVC
Full information on the voting for the approval of this technical report 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.
The committee has decided that the contents of this publication will remain unchanged until
the maintenance result 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.
TR 60725  IEC:2005 – 9 –
CONSIDERATION OF REFERENCE IMPEDANCES AND PUBLIC SUPPLY
NETWORK IMPEDANCES FOR USE IN DETERMINING DISTURBANCE
CHARACTERISTICS OF ELECTRICAL EQUIPMENT HAVING A RATED
CURRENT ≤ 75A PER PHASE
1 Scope
This technical report records the information that was available and the factors that were
taken into account in arriving at the reference impedances that were formerly incorporated in
)
IEC 60555 , but which are now incorporated into some sections of IEC 61000-3.
In addition, information is given on the impedances of public supply networks associated with
service current capacities ≥100 A per phase.
2 Normative references
The following referenced documents are indispensable for the application of this document.
For dated references, only the edition cited applies. For undated references, the latest edition
of the referenced document (including any amendments) applies.
IEC 61000-3-3, Electromagnetic compatibility (EMC) – Part 3: Limits – Section 3: Limitation of
voltage fluctuations and flicker in low-voltage supply systems for equipment with rated current
2)
≤ 16 A
Amendment 1 (2001)
IEC 61000-3-11, Electromagnetic compatibility (EMC) – Part 3-11: Limits – Limitation of
voltage changes, voltage fluctuations and flicker in public low-voltage supply systems –
Equipment with rated current ≤ 75 A and subject to conditional connection
IEC 61000-3-12, Electromagnetic compatibility (EMC) – Part 3-12: Limits – Limits for
harmonic currents produced by equipment connected to public low-voltage systems with input
current > 16 A and ≤ 75 A per phase
3 Systems of supply
3.1 Three-phase supply systems
Three-phase, four-wire, distribution systems are used worldwide to supply low-voltage
consumers, with nominal voltages in the region of 230/400 V.
To conform with IEC standard voltages, these system are described as 230/400 V throughout
this report.
___________
)
IEC 60555 (all parts), Disturbances in supply systems caused by household appliances and similar electrical
equipment (withdrawn)
2)
A consolidated edition 1.1 (2002) exists, including IEC 61000-3-3:1994 and its Amendment 1 (2001). It has
been published under the title of Electromagnetic compatibility (EMC) – Part 3-3: Limits – Limitation of voltage
changes, voltage fluctuations and flicker in public low-voltage supply systems, for equipment with rated current
≤16 A per phase and not subject to conditional connection

TR 60725  IEC:2005 – 11 –
There is considerable variation in the way in which the supplies to individual consumers are
connected to three-phase systems.
In some countries, all four wires are taken into the consumer’s premises, allowing the use of
three-phase 400 V for large loads, with small appliances and lighting circuits connected
between one line and neutral at 230 V.
In other countries, three wires are taken into the consumer’s premises, allowing the use of
400 V across two phases for large loads, with small appliances and lighting circuits connected
between one line and neutral at 230 V.
In other countries, of which the United Kingdom is an example, it is unusual to take more than
one phase into a residential consumer’s premises. Consequently both large loads less than
15 kVA and lighting circuits are supplied between line and neutral at 230 V.
3.2 Single-phase supply systems
In some countries, of which the United States of America and Japan are examples, a single-
phase, three-wire distribution is used. Large loads are connected across the outer wires at
230 V whilst small appliances and lighting circuits are connected between one outer and the
centre wire at 115 V. This leads to quite different supply impedances from those of three-
phase distribution systems and may require different reference impedances.
Recommended values of reference impedances appropriate to single-phase three-wire
distribution systems and all systems operating at a fundamental frequency of 60 Hz, are not
provided in this document; this subject is to receive further study when sufficient technical
information is released by countries operating such systems.
4 Supply impedances
4.1 Typical residential premises
The supply system impedance associated with the supply to the premises of a typical
residential consumer is determined by the average value of maximum power demand of all the
consumers connected to a typical network and the steady state voltage drop at maximum load
used to design the system.
Information on the supply system impedance was collected from as many countries as
possible and is presented in Table 1. The impedance to be considered was the impedance up
to the point of common coupling with other consumers. However, in many systems,
particularly where there were several apartments in the same building, the point of common
coupling was close to the metering point. Hence the impedance figures obtained usually
included both the supply system impedance and the service connection impedance.
The phase-to-neutral impedance characteristics of three-phase supply systems, in which each
consumer is supplied at 230 V, 50 Hz, differ widely between countries as shown in Table 1.

TR 60725  IEC:2005 – 13 –
Table 1 – 1980 International survey of residential consumers’ complex supply
impedances, in ohms, for single-phase connections at 50 Hz
Percentage of consumers having supply impedances
equal to or less than the listed complex values
Country
98 % 95 % 90 % 85 %
Belgium – 0,63 + j0,33 0,32 + j0,17 0,28 + j0,15
France – 0,55 + j0,34 0,45 + j0,25 0,34 + j0,21
Germany – 0,45 + j0,25 0,36 + j0,21 0,31 + j0,17
a
Ireland 1,47 + j0,64 1,26 + j0,60 1,03 + j0,55 0,94 + j0,43
Italy – 0,59 + j0,32 0,48 + j0,26 0,44 + j0,24
0,70 + j0,25 0,41 + j0.21 0,32 + j0,17
Netherlands –
Switzerland – 0,60 + j0,36 0,42 + j0,25 0,30 + j0,18
United Kingdom 0,46 + j0,45 – 0,25 + j0,23 –
USSR – 0,63 + j0,30 0,50 + j0,26 –
a
System impedances for residential consumers in Poland are similar to those in Ireland.

Since 1981 when the impedance survey was published as Table 1, there has been natural
development and reinforcement of public supply networks and the values in the 90 % column,
on which the reference impedances for residential supplies were based, are now more
relevant to the 95 % column because supply impedances have been reduced overall.
The Korean Agency for Technology and Standards completed a comprehensive national
survey of network impedances associated with 60 Hz, 380/220 V low-voltage supply systems
in March 2004 and provides information that the following, 95% probability, network
impedances are appropriate to Korea:
− single-phase two-wire 220 V, service capacities < 100 A per phase, (0,67 + j0,37) Ω;
− three-phase four-wire 380 V, service capacities < 100 A per phase, (0,33 + j0,20) Ω .
4.2 Large residential, commercial and light industrial premises
The premises considered in this clause have service current capacities equal to or in excess
of 100 A per phase.
It is anticipated that the number of requests from consumers and their agents to distribution
network operators for information relating to the system impedance at their supply terminals
will increase as a consequence of the publication of IEC 61000-3-11 and the procedure for
the conditional connection of equipment that it promulgates.
In order to assist distribution network operating companies worldwide in determining a
practical value of actual supply impedance at a particular consumers’ premises and to assist
manufacturers in assessing the marketability of their products in particular countries
worldwide, a basic approach to the determination of maximum supply impedance has been
developed and is given in Annex A.

TR 60725  IEC:2005 – 15 –
The following values of supply impedance have been obtained by application of the method
given in Annex A, based on the assumptions that:
a) the distribution transformer has a rating of 500 kVA, a 3 % voltage regulation or a 2,68 %
reactance;
b) there is 95 % probability of occurrence, i.e. 5 % of consumers, are likely to have a supply
system impedance greater than the tabled values.
If necessary, these supply impedances, or the maximum supply impedances listed in
Tables A.1 and A.2, may be amended to represent national or particular public supply
networks by use of Clause A.5.
The Korean Agency for Technology and Standards completed a comprehensive national
survey of network impedances associated with 60 Hz, 380/220 V low-voltage supply systems
in March 2004 and provides information that the following, 95% probability, network
impedances are appropriate to Korea:
− single-phase two-wire 220 V, service capacities ≥100 A per phase, (0,29 + j0,33) Ω;
− three-phase four-wire 380 V, service capacities ≥100 A per phase, (0,26 + j0,30) Ω.
4.2.1 Supply impedances relevant to the connection of three-phase equipment
Table 2 contains, under the assumptions stated in 4.2, the values of the modulus, in ohms, of
the supply impedance of the line-conductors of 230/400 V, 50 Hz public electricity supply
networks relevant to three-phase services, the various statutory voltage ranges declared to
consumers and service capacities in common use.
Table 2 – Modulus values of supply impedance, in ohms at 50 Hz,
relevant to the connection of three-phase equipment
and having a 95 % probability of not being exceeded
Service capacity in amperes per phase
Declared voltage range in
per cent
150 A 200 A 300 A 400 A 600 A
8 0,09 0,06 0,04 0,03 0,02
9 0,10 0,07 0,05 0,04 0,03
10 0,11 0,08 0,05 0,04 0,03
11 0,12 0,09 0,06 0,05 0,03
12 0,14 0,10 0,07 0,05 0,03
13 0,15 0,11 0,08 0,06 0,04
14 0,17 0,13 0,08 0,07 0,04
15 0,18 0,14 0,09 0,07 0,05
16 0,20 0,15 0,10 0,08 0,05
17 0,21 0,16 0,10 0,08 0,05
18 0,22 0,17 0,11 0,09 0,06
19 0,24 0,18 0,12 0,09 0,06
20 0,25 0,19 0,13 0,10 0,06
TR 60725  IEC:2005 – 17 –
4.2.2 Supply impedances relevant to the connection of single-phase equipment
Table 3 contains, under the assumptions stated in 4.2, the values of the modulus, in ohms, of
the supply impedance of the line-to-neutral conductors of 230/400 V, 50 Hz public electricity
supply networks relevant to the connection of single-phase equipment to three-phase 4-wire
services.
Table 3 – Modulus values of supply impedance, in ohms at 50 Hz,
relevant to the connection of single-phase equipment
and having a 95 % probably of not being exceeded
Service capacity in amperes per phase
Declared voltage range in per
cent
150 A 200 A 300 A 400 A 600 A
8 0,13 0,10 0,06 0,05 0,03
9 0,15 0,12 0,08 0,06 0,04
10 0,18 0,13 0,09 0,07 0,04
11 0,20 0,15 0,10 0,08 0,05
12 0,23 0,17 0,11 0,08 0,06
13 0,25 0,19 0,12 0,09 0,06
14 0,27 0,20 0,14 0,10 0,07
15 0,30 0,22 0,15 0,11 0,07
16 0,32 0,24 0,16 0,12 0,08
17 0,34 0,26 0,17 0,13 0,09
18 0,37 0,28 0,18 0,14 0,09
19 0,39 0,29 0,20 0,15 0,10
20 0,42 0,31 0,21 0,16 0,10
5 Reference impedances
Recommended values of reference impedances appropriate to distribution systems operating
at a fundamental frequency of 60 Hz are not provided in this document; this subject is to
receive further study when sufficient technical information is released by countries operating
such systems.
5.1 Reference impedances for equipment with current ratings ≤16 A
Equipment having current ratings ≤16 A is mainly connected in premises having service
current capacities less than 100 A per phase. Such premises are predominantly in residential
supply areas, which were surveyed in 1980, and reference impedances relevant to the
connection of equipment having current ratings ≤16 A have therefore been derived from the
values given in Table 1.
It was intended that the reference impedances should represent existing system impedances
and have values that could be used to assess the emissions of equipment against voltage
limits with a view to ensuring that connection of equipment to a public supply network would
not cause undue voltage disturbance and distortion.

TR 60725  IEC:2005 – 19 –
It has not proved possible to find an automatic and logical way of relating the reference
impedance to the range of system impedances. It was recognised that to say that 10 % of
consumers had supply impedances greater than a given value did not imply that 10 % of
consumers would be disturbed. A consumer at the far end of a line causes less disturbance
(by voltage fluctuation or harmonic distortion) to consumers nearer to the source than to his
immediate neighbour.
Divergence of views about the use of a single reference impedance may be summarized as
follows.
a) Some countries with high impedance networks do not consider it economically possible to
reinforce their networks.
b) Some countries with high impedance networks have no need to reinforce their networks
because they have readily available alternative fuels for cooking and heating appliances.
c) Some countries are not concerned with the switching of significant loads at 230 V because
they connect large appliances to two or three phases at 400 V.
The values in the following subclauses were chosen as reference impedances and take
account of experience with the use of existing appliances on existing systems as well as the
survey values of system impedance presented in Table 1.
5.1.1 Three-phase, four-wire, 230 V supplies
Adoption of the following test reference impedances, Z , is recommended:
ref
Phase conductor
0,24 + j0,15 Ω
Neutral conductor 0,16 + j0,10 Ω

0,40 + j0,25 Ω
5.1.2 Single-phase, two-wire 230 V supplies
In this category Ireland has a network in which a high percentage of consumers have a supply
impedance greater than 0,4 + j0,25 Ω
...