SECTION 5:EXCESS CURRENT PROTECTION
SECTION 5
EXCESS CURRENT PROTECTION
501 Every phase conductor in an installation, other than an earth conductor or those exempted under clause 504 shall be protected against excess current by a fuse or circuit-breaker fitted at the origin of a circuit of which the conductor forms a part.
502 The current rating of every fuse employed for the above purpose shall not exceed the current rating of the conductor to be protected. Fuses shall be of a type approved by the EDD.
503 The current rating of every circuit breaker employed for the purpose of affording excess current protection shall be such that it will operate within 4 hours when subjected to a sustained excess of 1.45 times the rating of the conductor to be protected.
504 Clause 501 may be omitted in the following cases:
- Circuits in which the omission of excess current protection is necessary to prevent danger, e.g.. shunt trip circuit of a circuit breaker.
- Auxiliary circuits of apparatus contained entirely within the enclosure of the apparatus.
505 All fuses employed within the electrical installations shall be H.R.C. cartridge fuses. Rewireable fuses shall not be employed.
506 The rating of the excess current protective device indicated in clauses 502 and 503 above applies to the phase conductor only and in a 3 phase, 4 wire installation, having a reduced neutral conductor, the excess current protective device need not be related to the rating of the neutral conductor.
507 Where floor distribution boards are connected by means of tap off units from adjacent busbar trunking the excess current protection may be located at the load end and not at the origin of the circuit provided that both are located in the same room.
508 Each excess current protective device shall be fully suitable for withstanding the maximum short circuit current attainable at that location.
509 The selection and ratings of excess current protective devices throughout an installation shall be so arranged that proper discrimination is ensured during operation of these excess current protective devices.
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