2.7.1 Basic requirements
To protect against excessive current, short-circuits and earth faults in PRIMARY CIRCUITS, protective devices shall be included either as integral parts of the equipment or as parts of the building installation, subject to the following, a), b) and c):
a) except as detailed in b) and c), protective devices necessary to comply with the requirements of 5.3 shall be included as parts of the equipment;
b) for components in series with the mains input to the equipment such as the supply cord, appliance coupler, r.f.i. filter and switch, short-circuit and earth fault protection may be provided by protective devices in the building installation;
c) it is permitted for PLUGGABLE EQUIPMENT TYPE B or PERMANENTLY CONNECTED EQUIPMENT, to rely on dedicated overcurrent and short-circuit protection in the building installation, provided that the means of protection, e.g. fuses or circuit breakers, is fully specified in the installation instructions.
protective earthing and protective bonding
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If reliance is placed on protection in the building installation, the installation instructions shall so state, except that for PLUGGABLE EQUIPMENT TYPE A the building installation shall be regarded as providing protection in accordance with the rating of the wall socket outlet.
Note deleted
Compliance is checked by inspection.
This subclause has been declared ‘void’. Short-circuit backup protection
Unless appropriate short-circuit backup protection is provided, protective devices shall have adequate breaking (rupturing) capacity to interrupt the maximum fault current (including short- circuit current) which can flow.
For PERMANENTLY CONNECTED EQUIPMENT or PLUGGABLE EQUIPMENT TYPE B, it is permitted for short-circuit backup protection to be in the building installation.
For PLUGGABLE EQUIPMENT TYPE A, the building installation is considered as providing short- circuit backup protection.
NOTE If fuses complying with IEC 60127 are used in PRIMARY CIRCUITS, they should have high breaking capacity (1 500 A) if the prospective short-circuit current exceeds 35 A or ten times the current rating of the fuse, whichever is greater.
Compliance is checked by inspection and by the tests of 5.3.
Protective systems or devices in PRIMARY CIRCUITS shall be in such a number and located so as to detect and to interrupt the overcurrent flowing in any possible fault current path (for example, line-to-line, line-to-neutral, line to protective earth conductor or line to PROTECTIVE BONDING CONDUCTOR).
No protection is required against earth faults in equipment that either:
− has no connection to earth; or
− has DOUBLE INSULATION or REINFORCED INSULATION between the PRIMARY CIRCUIT and all parts connected to earth.
NOTE 1 Where DOUBLE INSULATION or REINFORCED INSULATION is provided, a short-circuit to earth would be considered to be two faults.
In a supply using more than one line conductor to a load, if a protective device interrupts the neutral conductor, it shall also interrupt all other supply conductors. Single-pole protective devices, therefore, shall not be used in such cases.
Compliance is checked by inspection and, where necessary, by simulation of single fault conditions (see 1.4.14).
NOTE 2 For protective devices that are an integral part of the equipment, examples of the number and location of fuses or circuit-breaker poles necessary to provide fault current interruption in commonly encountered supply systems are given in informative Table 2F for single-phase equipment or subassemblies and in informative Table 2G for three-phase equipment. The examples are not necessarily valid for protective devices external to the equipment.
2.7.4 Number and location of protective devices 2.7.2
2.7.3
Table 2F – Informative examples of protective devices in single-phase equipment or subassemblies
Equipment supply connections Protection against
Minimum number of fuses or
circuit-breaker poles Location
Earth faults 1 Line conductor
Case A:
Equipment to be connected to power distribution systems with earthed neutral reliably identified, except for case C below
Overcurrent 1 Either of the two
conductors
Earth faults 2 Both conductors
Case B:
Equipment to be connected to any supply, including IT power distribution systems and supplies with reversible
plugs, except for case C below Overcurrent 1 Either of the two conductors
Earth faults 2 Each line conductor
Case C:
Equipment to be connected to three-wire power distribution systems with earthed
neutral reliably identified Overcurrent 2 Each line conductor
Table 2G – Informative examples of protective devices in three-phase equipment
Power distribution system Number of supply conductors
Protection against
Minimum number of fuses or circuit-
breaker poles Location Three-phase without neutral 3 Earth faults 3 All three conductors
Overcurrent 2 Any two conductors
With earthed neutral (TN or TT) 4 Earth faults 3 Each line conductor
Overcurrent 3 Each line conductor
With unearthed neutral 4 Earth faults 4 All four conductors
Overcurrent 3 Each line conductor
2.7.5 Protection by several devices
Where protective devices are used in more than one pole of a supply to a given load, those devices shall be located together. It is permitted to combine two or more protective devices in one component.
Compliance is checked by inspection.
EN 60950-1:2006+A12:2011 (E)
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2.7.6 Warning to service persons
Suitable marking shall be provided on the equipment or a statement shall be provided in the servicing instructions to alert a SERVICE PERSON to a possible hazard, where both of the following conditions exist:
− fuse is used in the neutral of single-phase equipment either permanently connected or provided with a non-reversible plug; and
− after operation of the fuse, parts of the equipment that remain energized might represent a hazard during servicing.
The following or similar wording is regarded as suitable:
CAUTION
DOUBLE POLE/NEUTRAL FUSING
As an alternative to the above wording, use of the following combination of representative symbols, which includes the electric shock hazard symbol ISO 3864, No. 5036, the fuse symbol IEC-60417- 5016 (DB:2002-10), and an indication that the fuse is in the neutral N, is permitted. However in this case, the statement shall also be provided in the servicing instructions.
Compliance is checked by inspection.