Guide to the Wiring Regulations
Table C 4.3 Fault ratings of common devices. Device type
Fault current capacity (kA)
Circuit-breakers to BS EN 60898 and BS EN 61009 1
1
Icn Ics 1.5 (1.5) 3.0 (3.0) 4.5 (4.5) 6 (6.0) (7.5) 16
Circuit-breakers to BS EN 60947–2
Varies, specified by manufacturer
Cartridge fuse to BS 1361 type I Type II
16.5 33.0
General purpose fuse to BS 88 Part 2.1 Part 6
50 at 400 V 16.5 at 230 V 80.0 at 400 V
Semi-enclosed fuse to BS 3036 with category of duty
S1A-1 S2A-2 S4A-4
Circuit-breakers to BS 3871
M1–1 M1.5–1.5 M3–3 M4.5–4.5 M6–6 M9–9
Note 1: Two rated short-circuit ratings are defined in BS EN 60898 and BS EN 61009: Icn is the rated short-circuit capacity (marked on the device), Ics is the service short-circuit capacity. The difference between the two is the condition of the circuit breaker after manufacturer’s testing. Icn is the maximum fault current the breaker can interrupt safely, although the breaker may no longer be usable. Ics is the maximum fault current the breaker can interrupt safely without loss of performance. The Icn value is normally marked on the device in a rectangle, e.g. 6000 For the majority of applications the prospective fault current at the terminals of the circuit-breaker should not exceed this value.
I is the effective short-circuit current in amperes, due account being taken of the current limiting effect of the circuit impedances k is a factor taking account of the resistivity, temperature coefficient and heat capacity of the conductor material, and the appropriate initial and final temperatures. It should be noted that in this application of Equation 5, the disconnection time should not be taken as 5 s, but is taken from the time-current characteristic for the
C
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