IEC TR 60269-5:2010
(Main)Low-voltage fuses - Part 5: Guidance for the application of low-voltage fuses
Low-voltage fuses - Part 5: Guidance for the application of low-voltage fuses
IEC/TR 60269-5:2010 serves as an application guide for low-voltage fuses, shows how current-limiting fuses are easy to apply to protect today's complex and sensitive electrical and electronic equipment. This guidance specifically covers low-voltage fuses up to 1 000 V a.c. and 1 500 V d.c. designed and manufactured in accordance with IEC 60269 series. This guidance provides important facts about as well as information on the application of fuses.
Fusibles basse tension - Partie 5: Lignes directrices pour l'application des fusibles basse tension
La CEI/TR 60269-5:2010 est un guide d'application des fusibles basse tension, montre que les fusibles limiteurs de courant sont faciles à utiliser pour protéger le matériel électronique complexe et sensible d'aujourd'hui. Ces lignes directrices couvrent spécifiquement les fusibles basse tension de tensions jusqu'à 1 000 V en courant alternatif et 1 500 V en courant continu selon la série CEI 60269. Elles fournissent des informations sur les fusibles ainsi que sur leurs applications.
[Not translated]
General Information
Relations
Standards Content (Sample)
IEC/TR 60269-5 ®
Edition 1.0 2010-09
TECHNICAL
REPORT
RAPPORT
TECHNIQUE
colour
inside
Low-voltage fuses –
Part 5: Guidance for the application of low-voltage fuses
Fusibles basse tension –
Partie 5: Lignes directrices pour l’application des fusibles basse tension
IEC/TR 60269-5:2010
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IEC/TR 60269-5 ®
Edition 1.0 2010-09
TECHNICAL
REPORT
RAPPORT
TECHNIQUE
colour
inside
Low-voltage fuses –
Part 5: Guidance for the application of low-voltage fuses
Fusibles basse tension –
Partie 5: Lignes directrices pour l’application des fusibles basse tension
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
X
CODE PRIX
ICS 29.120.50 ISBN 978-2-88912-175-5
– 2 – TR 60269-5 © IEC:2010
CONTENTS
FOREWORD.5
INTRODUCTION.7
1 Scope.8
2 Normative references .8
3 Terms and definitions .9
4 Fuse benefits.10
5 Fuse construction and operation.11
5.1 Components .11
5.2 Fuse-construction.11
5.2.1 Fuse link.11
5.2.2 Fuse-link contacts .13
5.2.3 Indicating device and striker .13
5.2.4 Fuse-base .13
5.2.5 Replacement handles and fuse-holders .13
5.3 Fuse operation .14
5.3.1 General .14
5.3.2 Fuse operation in case of short-circuit .14
5.3.3 Fuse operation in case of overload .14
6 Fuse-combination units .15
7 Fuse selection and markings .16
8 Conductor protection .18
8.1 General .18
8.2 Type gG .18
8.3 Types gN and gD .19
8.4 Types gR and gS.19
8.5 Protection against short-circuit current only.19
9 Selectivity of protective devices.20
9.1 General .20
9.2 Selectivity between fuses .21
9.2.1 Verification of selectivity for operating time ≥ 0,1 s .21
9.2.2 Verification of selectivity for operating time < 0,1 s .22
9.2.3 Verification of total selectivity .22
9.3 Selectivity of circuit-breakers upstream of fuses .22
9.3.1 General .22
9.3.2 Verification of selectivity for operating time ≥ 0,1 s .22
9.3.3 Verification of selectivity for operating time < 0,1 s .23
9.3.4 Verification of total selectivity .23
9.4 Selectivity of fuses upstream of circuit-breakers .23
9.4.1 General .23
9.4.2 Verification of selectivity for operating time ≥ 0,1 s .23
9.4.3 Verification of selectivity for operating time < 0,1 s .23
9.4.4 Verification of total selectivity .23
10 Short-circuit damage protection .25
10.1 General .25
10.2 Short-circuit current paths .25
TR 60269-5 © IEC:2010 – 3 –
10.3 Current limitation.26
10.4 Rated conditional short-circuit current, rated breaking capacity .26
11 Protection of power factor correction capacitors .26
12 Transformer protection .27
12.1 Distribution transformers with a high-voltage primary .27
12.2 Distribution transformers with a low-voltage primary.28
12.3 Control circuit transformers .28
13 Motor circuit protection .28
13.1 General .28
13.2 Fuse and motor-starter coordination .29
13.3 Criteria for coordination at the rated conditional short-circuit current I .29
q
13.4 Criteria for coordination at the crossover current I .30
co
13.5 Criteria for coordination at test current “r”.31
14 Circuit-breaker protection .31
15 Protection of semiconductor devices .31
16 Fuses in enclosures.32
16.1 Limiting temperature of type gG fuse-links according to IEC 60269-2 –
System A.32
16.2 Other fuse-links.33
17 DC applications .33
17.1 Short-circuit protection .33
17.2 Overload protection .33
17.3 Time-current characteristics .34
18 Automatic disconnection for protection against electric shock for installations in
buildings.35
18.1 General .35
18.2 Principle of the protection.35
18.3 Examples .37
Annex A (informative) Coordination between fuses and contactors/motor-starters.38
Bibliography.48
Figure 1 – Typical fuse-link according to IEC 60269-2 .12
Figure 2 – Typical fuse-link according to IEC 60269-2 .13
Figure 3 – Current-limiting fuse operation .14
Figure 4 – Fuse operation on overload.15
Figure 5 – Selectivity – General network diagram .20
Figure 6 – Verification of selectivity between fuses F and F for operating time t ≥ 0,1 s .21
2 4
Figure 7 – Verification of selectivity between circuit-breaker C and fuses F and F .22
2 5 6
Figure 8 – Verification of selectivity between fuse F and circuit-breaker C for
2 3
operating time t ≥ 0,1 s .24
Figure 9 – Verification of selectivity between fuse F and circuit-breaker C for
2 3
operating time t < 0,1 s .25
Figure 10 – Fuse and motor-starter coordination.30
Figure 11 – DC circuit .33
Figure 12 – DC breaking operation .34
Figure 13 – Fuse operating time at various d.c. circuit time constants.35
– 4 – TR 60269-5 © IEC:2010
Figure 14 – Time-current characteristic.36
Figure A.1 – Collation of cut-off currents observed in successful coordination at I .39
q
Figure A.2 – Pre-arcing and operating I t values of fuses used in successful
coordination tests as a function of contactor rated current AC3.40
Figure A.3 – Pre-arcing and operating I t values of fuses used in successful
coordination tests as a function of fuse rated current I .41
n
Figure A.4 – Illustration of the method of selection of the maximum rated current of a
fuse for back-up protection of a contactor of rating I = X amperes .45
e
Figure A.5 – Withstand capabilities of a range of contactors and associated overload
relays at test current "r" .46
Figure A.6 – Illustration of a method of deriving curves of maximum peak current at
test current "r" as a function of fuse rated current (these derived curves can be used in
the same way as illustrated in Figure A.4).47
Table 1 – Definitions and symbols of switches and fuse-combination units.16
Table 2 – Fuse application.17
Table 3 – Maximum operational voltage of fuse-links .18
Table 4 – Fuse selection for power factor correction capacitors (fuses according to
IEC 60269-2, system A) .27
Table 5 – Time constants of typical d.c. circuits .34
Table A.1 – Examples of typical fuse-link ratings used for motor-starter protection
illustrating how the category of fuse-link can influence the optimum current rating .38
Table A.2 (Table 12 of IEC 60947-4-1) – Value of the prospective test current
according to the rated operational current.43
Table A.3 – Types of coordination.44
TR 60269-5 © IEC:2010 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
LOW-VOLTAGE FUSES –
Part 5: Guidance for the application of low-voltage fuses
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,
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2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
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3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
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5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
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6) All users should ensure that they have the latest edition of this publication.
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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.
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 60269-5, which is a technical report, has been prepared by subcommittee 32B: Low-
voltage fuses, of IEC technical committee 32: Fuses.
This technical report cancels and replaces IEC/TR 61818, published in 2003, and IEC/TR
61459, published in 1996. It constitutes a minor revision by amending and restructuring the
two replaced publications.
– 6 – TR 60269-5 © IEC:2010
The text of this technical report is based on the following documents:
Enquiry draft Report on voting
32B/554/DTR 32B/566/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.
A list of all parts of the IEC 60269 series, under the general title: Low-voltage fuses, can be
found on the IEC website.
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.
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 document using a
colour printer.
TR 60269-5 © IEC:2010 – 7 –
INTRODUCTION
Fuses protect many types of equipment and switchgear against the effects of over-current
which can be dramatic:
• thermal damage of conductors or bus-bars;
• vaporisation of metal;
• ionisation of gases;
• arcing, fire, explosion,
• insulation damage.
Apart from being hazardous to personnel, significant economic losses can result from
downtime and the repairs required to restore damaged equipment.
Modern fuses are common overcurrent protective devices in use today, and as such provide
an excellent cost effective solution to eliminate or minimize the effects of overcurrent.
– 8 – TR 60269-5 © IEC:2010
LOW-VOLTAGE FUSES –
Part 5: Guidance for the application of low-voltage fuses
1 Scope
This technical report, which serves as an application guide for low-voltage fuses, shows how
current-limiting fuses are easy to apply to protect today's complex and sensitive electrical and
electronic equipment. This guidance specifically covers low-voltage fuses up to 1 000 V a.c.
and 1 500 V d.c. designed and manufactured in accordance with IEC 60269 series. This
guidance provides important facts about as well as information on the application of fuses.
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 60050-441, International Electrotechnical Vocabulary (IEV) – Chapter 441: Switchgear,
controlgear and fuses
IEC/TR 60146-6, Semiconductor convertors – Part 6: Application guide for the protection of
semiconductor convertors against overcurrent by fuses
IEC 60269 (all parts), Low-voltage fuses
IEC 60269-1, Low-voltage fuses – Part 1: General requirements
IEC 60269-2, Low-voltage fuses – Part 2: Supplementary requirements for fuses for use by
authorized persons (fuses mainly for industrial application) – Examples of standardized fuses
system A to J
IEC 60269-3, Low-voltage fuses – Part 3: Supplementary requirements for fuses for use by
unskilled persons – Examples of standardized fuses system A to F
IEC 60269-4, Low-voltage fuses – Part 4: Supplementary requirements for fuse-links for the
protection of semiconductor devices
IEC 60364-4-41, Low-voltage electrical installations – Part 4-41: Protection for safety –
Protection against electric shock
IEC 60364-4-43, Low-voltage electrical installations – Part 4-43: Protection for safety –
Protection against overcurrent
IEC 60364-5-52, Low-voltage electrical installations – Part 5-52: Selection and erection of
electrical equipment – Wiring systems
IEC/TR 60787, Application guide for the selection of high-voltage current-limiting fuse-links
for transformer circuits
IEC 60947 (all parts), Low-voltage switchgear and controlgear
TR 60269-5 © IEC:2010 – 9 –
IEC 60947-3, Low-voltage switchgear and controlgear – Part 3: Switches, disconnectors,
switch-disconnectors and fuse-combination units
IEC 60947-4-1, Low-voltage switchgear and controlgear – Part 4-1: Contactors and motor-
starters – Electromechanical contactors and motor-starters
CEI 61912-1 : Low-voltage switchgear and controlgear – Overcurrent protective devices –
Part 1 :Application of short-circuit ratings
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
switch (mechanical)
mechanical switching device capable of making, carrying and breaking currents under normal
circuit conditions, which may include specified operating overload conditions and also
carrying, for a specified time, currents under specified abnormal conditions such as those of
short-circuits
NOTE A switch may be capable of making but not breaking, short-circuit currents.
[IEC,60050-441:1984, 441-14-10]
3.2
disconnector
mechanical switching device that, in the open position, complies with the requirements
specified for isolating function
NOTE Some disconnectors may not be capable of switching load.
[IEC 60050-441:1984, 441-14-05, modified]
3.3
fuse-combination unit
combination of a mechanical switching device and one or more fuses in a composite unit,
assembled by the manufacturer or in accordance with his instructions
[IEC 60050-441:1984, 441-14-04, modified]
3.4
switch-fuse
switch in which one or more poles have a fuse in series in a composite unit
[IEC 60050-441:1984, 441-14-14]
3.5
fuse-switch
switch in which a fuse-link or a fuse-carrier with fuse-link forms the moving contact
[IEC 60050-441:1984, 441-14-17]
3.6
Switching device
SD
device designed to make or break the current in one or more electric circuits
NOTE A switching device may perform one or both of these operations.
[IEC 60050-441:1984, 441-14-01]
– 10 – TR 60269-5 © IEC:2010
3.7
short-circuit protective device
SCPD
device intended to protect a circuit or parts of a circuit against short-circuits by interrupting
them
3.8
overload protection
protection intended to operate in the event of overload on the protected section
[IEC 60050-448:1995, 448-14-31]
3.9
overload
operating conditions in an electrically undamaged circuit, which cause an over-current
[IEC 60050-441:1984, 441-11-08]
3.10
overcurrent
current exceeding the rated current
[IEC 60050-442:1998, 442-01-20]
3.11
rated conditional short-circuit current (of a switching device)
I
q
prospective current that a switching device, protected by a short-circuit protective device, can
satisfactorily withstand for the operating time of that device under test conditions specified in
the relevant product standard
3.12
selectivity of protection
ability of a protection to identify the faulty sections and/or phase(s) of a power system
[IEC 60050-448:1995, 448-11-06]
NOTE Whereas the terms “selectivity” and “discrimination” have a similar meaning according to the IEV
definitions, this report prefers and uses the term “selectivity” to express the ability of one over-current device to
operate in preference to another over-current device in series, over a given range of over-current. The effect of
standing load current on selectivity in the overload zone is also considered.
4 Fuse benefits
The current-limiting fuse provides complete protection against the effects of overcurrents by
protecting both, electric circuits and their components. Fuses offer a combination of
advantageous features, for example:
a) High breaking capacity (high current interrupting rating).
b) No need for complex short-circuit calculations.
c) Easy and inexpensive system expansion in case of increased fault currents.
d) High current limitation (low I t values).
e) Mandatory fault elimination before reenergizing.
Fuses cannot be reset, thus forcing the user to identify and correct the fault condition
before re-energizing the circuit.
f) Reliability.
No moving parts to wear out or become contaminated by dust, oil or corrosion. Fuse
replacement ensures protection is restored to its original level when the fuse is replaced.
TR 60269-5 © IEC:2010 – 11 –
g) Cost effective protection.
Compact size offers low cost overcurrent protection at high short-circuit levels.
h) No damage for starters and contactors (type 2 protection according to IEC 60947-4-1).
By limiting short-circuit energy and peak currents to extremely low levels, fuses are
particularly suitable for type 2 protection without damage to components in motor circuits.
i) Safe, silent operation.
No emission of gas, flames, arcs or other materials when clearing the highest levels of
short-circuit currents. In addition, the speed of operation at high short-circuit currents
significantly limits the arc flash hazard at the fault location.
j) Easy coordination.
Standardized fuse characteristics and a high degree of current limitation ensure effective
coordination between fuses and other devices.
k) Standardized performance
Fuse-links designed and manufactured in accordance with IEC 60269 series ensure
availability of replacements with standardized characteristics throughout the world.
l) Improved power quality.
Current-limiting fuses interrupt high fault currents in a few milliseconds, minimizing dips or
sags in system supply voltage.
m) Tamperproof.
Once installed, fuses cannot be modified or adjusted thus preserving their level of
performance and avoiding malfunction.
n) No maintenance.
Properly sized fuses require no maintenance, adjustments or recalibrations. They can
remain in service providing originally designed overcurrent protection levels for many
decades.
5 Fuse construction and operation
5.1 Components
A fuse is a protective device comprising
• the fuse-link,
• the fuse-base,
• the fuse-carrier or replacement handle.
These components may be integrated in a fuse combination unit.
5.2 Fuse-construction
5.2.1 Fuse link
Figures 1 and 2 show the design of typical low-voltage fuse-links for industrial application.
Such fuse-links are commonly called current-limiting or high breaking capacity fuse-links.
Fuse-links according to IEC 60269-2 (fuses for industrial application) are available in current
ratings up to 6 000 A.
Fuse-links according to IEC 60269-3 (fuses for household application) are available in current
ratings up to 100 A.
The fuse-element is usually made of flat silver or copper with multiple restrictions in the cross-
section, called notches. This restriction (or notch) pattern is an important feature of fuse
design, normally achieved by precision stamping.
– 12 – TR 60269-5 © IEC:2010
M-effect (see 5.3.3) material is added to the fuse-element to achieve controlled fuse operation
in the overload range. The purity of the fuse-element materials and their precise physical
dimensions are of vital importance for reliable fuse operation.
IEC 2061/10
Key
1 Blade contact
2 Fuse-elements
3 Fuse body
4 End cap
5 Filler
Figure 1 – Typical fuse-link according to IEC 60269-2
TR 60269-5 © IEC:2010 – 13 –
IEC 2062/10
Key
1 Blade contact
2 Fuse-element
3 Fuse body
4 Endplate (with gripping lug)
5 Indicator wire
6 M-effect material
7 Filler
8 Indicator
Figure 2 – Typical fuse-link according to IEC 60269-2
5.2.2 Fuse-link contacts
Fuse-link contacts provide electrical connection between the fuse-link and fuse-base or fuse
carrier. The contacts are made of copper or copper alloys and are typically protected against
the formation of non-conductive layers by plating.
5.2.3 Indicating device and striker
Some fuses are equipped with indicators or strikers for rapid recognition of fuse-link operation.
Fuses equipped with strikers also provide means for mechanical actuation (e.g. for a switch of
remote signalling) as well as a visual indication.
5.2.4 Fuse-base
The fuse-base is equipped with the matching contacts for accepting the fuse-link, connecting
means for cables or busbars and the base insulator.
5.2.5 Replacement handles and fuse-holders
Replacement handles or fuse-carriers, where applicable, enable changing fuse-links in a live
system under specified safety rules. They are made of insulating material and subjected to
– 14 – TR 60269-5 © IEC:2010
tests as required for safety tools. For some systems, fuse-carriers are an integral part of the
fuse-holder, eliminating the need for an external replacement handle.
5.3 Fuse operation
5.3.1 General
Fuses are designed to operate under both short-circuit and overload conditions. Typically
short-circuits are current levels at or above 10 times the fuse’s rating, and overloads are
current levels below 10 times the fuse’s rating.
5.3.2 Fuse operation in case of short-circuit
During a short-circuit, the restrictions (notches) all melt simultaneously forming a series of
arcs equal to the number of restrictions in the fuse element. The resulting arc voltage ensures
rapid reduction in current and forces it to zero. This action is called “current limitation”.
Fuse operation occurs in two stages (see Figure 3a and 3b):
• the pre-arcing (melting) stage (t ): the heating of the restrictions (notches) to the melting
m
point and associated vaporization of the material;
• the arcing stage (t ): the arcs begin at each notch and are then extinguished by the filler.
a
The operating time is the sum of the prearcing time and arcing time.
The energies generated by the current in the circuit to be protected during pre-arcing time and
2 2
operating time are represented by the pre-arcing I t and operating I t values, respectively.
The diagrams in Figure 3 illustrate the current-limiting ability of the fuse-link under short-
circuit conditions.
Note that the fuse-link cut-off current i is well below the peak value of the prospective current
c
I .
P
I
p
I
p
i(t) i(t)
i
c
i
c
t t t
m a t
m a
IEC 2063/10
IEC 2064/10
Figure 3a – DC current Figure 3b – AC current
Key
t pre-arcing time; t arcing time; I prospective current; i current limited by the fuse
m a p c
Figure 3 – Current-limiting fuse operation
5.3.3 Fuse operation in case of overload
During an overload, the “M-effect” material melts and an arc forms between the two parts of
the fuse element. The filler (typically clean granulated quartz) which surrounds the fuse
TR 60269-5 © IEC:2010 – 15 –
element quickly extinguishes the arc forcing the current to zero. As it cools, the molten filler
turns into a glass like material insulating each half of the fuse element from each other and
preventing arc re-ignition and further current flow. Fuse operation still occurs in two stages
(see Figures 4a and 4b):
• the pre-arcing (melting) stage (t ): the heating of the fuse element to the melting point of the
m
section containing the M-effect material. This period of time is typically longer than a few
milliseconds and is inversely dependent on the magnitude of the overload current. Low level
overloads result in long melting times from several seconds to several hours.
• the arcing stage (t ): the arc initiated at the M-effect section is then extinguished by the filler. This
a
time is dependent on the operating voltage
• Both stages make up the fuse operating time (t + t ).The energy generated in the circuit
m a
to be protected by the overload current during pre-arcing (melting) time and operating time
2 2
can still be represented by the pre-arcing I t and operating I t values, respectively;
however under overload conditions the pre-arcing I t value is so high it provides little
useful application data and the prearcing time is the preferred measure for times longer
than a few cycles or few time constants. In this case, arcing time is negligible compared to
the prearcing time.
t t
t
m m t
a a
Overload current Overload current
I
f
I
f
Time
Time
IEC 2065/10
IEC 2066/10
Figure 4a – AC current Figure 4b – DC current
Figure 4 – Fuse operation on overload
6 Fuse-combination units
Fuse-combination units integrate both circuit protection provided by fuse-links and circuit
switching provided by the switch in one unit. Fuse-combination units are standardized in
IEC 60947-3 (see Table 1).
Two different types of fuse-combination units are available:
• switch-fuses, switch-disconnector-fuses are switches connected in series with the fuse-
links and are usually operator independent devices with manual operation (snap action);
• fuse-disconnectors and fuse-switch-disconnectors which use the fuse-link itself to form the
moving part are usually operator dependent devices with manual operation.
Definitions can be found in IEC 60947-3 or in IEC 60050-441. The main ones are shown here
for easier reading and their full description can be found in Clause 3:
– switch (mechanical) (see 3.1);
– disconnector (see 3.2);
– fuse combination unit (see 3.3);
– switch-fuse (see 3.4);
Current (A)
Current (A)
– 16 – TR 60269-5 © IEC:2010
– fuse-switch (see 3.5).
From these basic definitions, there are many variations of these devices as shown in Table 1.
Table 1 – Definitions and symbols of switches and fuse-combination units
Function
Connecting and disconnecting Isolating Connecting, disconnecting
and isolating
Switch Disconnector Switch-disconnector
2.1 of IEC 60947-3 2.2 of IEC 60947-3 2.3 of IEC 60947-3
Fuse-combination unit, 2.4 of IEC 60947-3
Switch-fuse Disconnector-fuse Switch-disconnector-fuse
2.5 of IEC 60947-3 2.7 of IEC 60947-3 2.9 of IEC 60947-3
Fuse-switch Fuse-disconnector Fuse-switch disconnector
2.6 of IEC 60947-3 2.8 of IEC 60947-3 2.10 of IEC 60947-3
NOTE Subclause numbers given in this table refer to IEC 60947-3.
The note to the definition of the switch, i.e. stating that a switch may be capable of making but
not breaking, short-circuit currents, very clearly shows that a switch to IEC 60947-3 does not
provide short-circuit breaking capacity. In the case of a fuse-combination unit the fuse takes
over the breaking function.
Since most of the fuse-combination units with the fuse as an integral unit are designed as
fuse-switch disconnectors, or switch - disconnector - fuses, they may be used for
• switching under load,
• isolation,
• short-circuit protection.
The fuse(s) fitted to a fuse combination switch also protect the switch itself against the effects
of overcurrent.
7 Fuse selection and markings
To select the proper fuse the nature of the equipment to be protected and the power that has
to be interrupted, must be considered. With respect to power supply, the following parameters
shall be defined:
– system voltage (operational voltage);
– frequency (for d.c. applications, see Clause 17);
– prospective short-circuit current;
– full load current (operational current).
Current limiting fuse-links are designed with very high rated breaking capacity. They are
usually much higher than the minimum values specified in IEC 60269-2 and IEC 60269-3.
TR 60269-5 © IEC:2010 – 17 –
Fuse-links are available with rated breaking capacities that cover the highest prospective
current levels, that are met in service (e.g. up to 200 kA).
NOTE Fuse-links can be safely applied at lower values than the rated breaking capacity.
Fuse selection for a specific application involves consideration of the time-current
characteristics and breaking range. The time-current characteristics determine the field of
application, while the breaking range indicates whether fuses are to be used together with
additional overcurrent protection devices.
"Full range" means that the fuse can break any current able to melt the fuse-element up to the
rated breaking capacity. Full range fuses can be used as stand-alone protection devices.
"Partial range", or back-up fuses, are designed to interrupt short-circuit currents only.
They are generally used to back-up another overcurrent protection device, (e.g. motor starter
or circuit-breakers) at prospective currents exceeding the breaking capacity of the device
alone.
IEC 60269 series and its various fuse systems specify the gates of time-current
characteristics and the breaking range of the following fuses:
Table 2 – Fuse application
Type Application (characteristic) Breaking range
gG General purpose Full range
gM Motor circuit protection Full range
Partial range
aM Short-circuit protection of motor circuits
(back-up)
gN North American general purpose for conductor protection Full range
gD North American general purpose time-delay Full range
Partial range
aR Semiconductor protection
(back-up)
gR, gS Semiconductor and conductor protection Full range
gU General purpose for conductor protection Full range
gL, gF, gI, gII Former types of fuses for general purpose (replaced by gG type) Full range
Fuses for use by authorized persons (industrial fuses) are generally interchangeable. Each
fuse-link, fuse-base or fuse-holder is therefore legibly and permanently marked with the
following information:
• name of the manufacturer or trade name;
• manufacturer's identification reference enab
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