With reference to 434.3 and Figure D.3, the short-circuit protective device may be omitted for some applications such as transformers or measuring circuits) provided that, in accordance with the requirements of 434.3, the risk of short-circuit, fire and danger to persons is reduced to a minimum.
Figure D.3 – Situation where the short-circuit protective device may be omitted for some applications (refer to 434.3)
Note that a measuring circuit employing a current transformer must not be open-circuited otherwise an overvoltage will result.
For some applications, such as a magnetic crane, short-circuit protection may be omitted (refer to 434.3).
IEC 1247/08
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Annex E (informative)
List of notes concerning certain countries
Country Clause N°
Nature (permanent or less permanent according to IEC Directives)
Rationale (detailed justification
for the requested country note)
Wording
431.1.2 In the USA all phase conductors must be
provided with overcurrent protection
431.2.3 In the USA, the following applies: where it is
anticipated that there will be a significant number of or large sized nonlinear loads, the neutral may alternatively be sized to
accommodate the maximum anticipated current due to harmonic effects.
USA
433.1 In the USA the protective device operating
current is the same as the current-carrying capacity of the conductor
433.1 In the UK socket outlets can be supplied
through ring final circuits protected by a 32 A protective device complying with IEC 60269, IEC 60898, IEC 60947-2, or IEC 61009-1, wired with copper conductors having phase and neutral conductors with a minimum cross- sectional area of 2,5mm2 except for 2 core mineral insulated cables complying with the relevant IEC standard for which the minimum cross-sectional area is 1,5 mm². Such ring final circuits are deemed to meet the requirements of 433.1 if the current-carrying capacity (Iz) of the cable is not less than 20 A, and if, under the intended conditions of use, the load current in any part of the ring is unlikely to exceed for long periods the current carrying capacity (Iz) of the cable.
UK
433.1 In the UK socket outlets can be supplied
through ring final circuits protected by a 32 A protective device with or without unfused spurs
433.1 In Ireland socket outlets can be supplied
through ring final circuits protected by a 32 A protective device complying with IEC 60269, IEC 60898, IEC 60947-2, or IEC 61009-1 wired with copper conductors having phase and neutral conductors with a minimum cross- sectional area of 2,5mm2 except for 2 core mineral insulated cables complying with the relevant IEC standard for which the minimum cross-sectional area is 1,5 mm² . Such ring final circuits are deemed to meet the requirements of 433.1 if the current-carrying capacity (Iz) of the cable is not less than 20 A, and if under the intended conditions of use, the load current in any part of the ring is unlikely to exceed for long periods the current-carrying capacity (Iz) of the cable
433.1 In Ireland socket outlets can be supplied
through ring final circuits protected by a 32 A protective device with or without unfused spurs
433.3.1 In Ireland indent c) does not apply.
Ireland
434.3 In Ireland 434.3d does not apply in Ireland
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List of notes concerning certain countries (continued)
Country Clause N° Nature (permanent or less permanent according to IEC Directives)
Rationale (detailed justification
for the requested country note)
Wording
433.2.2 In Germany, Annex D is not applicable
433.3.1 In Germany, devices for protection against
overload need not be provided also in the following situation:
e) distribution circuits comprising cables laid in the ground or overhead lines where overloading of the circuits will not cause danger
433.3.1 In Germany, Annex C is not applicable
433.3.2.1 b) In Germany, item b) is as follows:
b) protection of each single current using equipment by its own RCD that will operate immediately on a second fault
433.3.2.1 c) In Germany, item c) is as follows:
c) use of insulation monitoring device which either:
- causes the disconnection of the circuit when the first fault occurs, or
- gives a signal indicating the presence of a fault. The fault shall be rectified according to the operational requirements and recognizing the risk from a second fault.
434.2.1 In Germany, NOTE 1 is as follows:
NOTE 1 This condition may be obtained for example by reinforcing the protection of the wiring against external influences. ensuring inherently short-circuit and earth fault proof installation.
434.3 In Germany, the omission of devices for
protection against short-circuit is allowed in distribution circuits comprising cables laid in the ground or overhead lines
Annex C In Germany, Annex C is not applicable
Germany
Annex D In Germany, Annex D is not applicable
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Bibliography
IEC 60269-1: Low-voltage fuses – Part 1: General requirements
IEC 60287-1-3, Electric cables – Calculation of the current rating – Part 1-3: Current rating equations (100 % load factor) and calculation of losses – Current sharing between parallel single-core cables and calculation of circulating current losses
IEC 60364-5-54:2002, Electrical installations of buildings – Part 5-54: Selection and erection of electrical equipment – Earthing arrangements, protective conductors and protective bonding conductors
IEC 60439-2, Low-voltage switchgear and controlgear assemblies – Part 2: Particular requirements for busbar trunking systems (busways)
IEC 60947-1: Low-voltage switchgear and controlgear – Part 1: General rules
IEC 60947-4-1, Low-voltage switchgear and controlgear – Part 4-1: Contactors and motor- starters – Electromechanical contactors and motor-starters
IEC 61557-9, Electrical safety in low voltage distribution systems up to 1 000 V a.c. and 1 500 V d.c. – Equipment for testing, measuring or monitoring of protective measures – Part 9:
Equipment for insulation fault location in IT systems
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