Chapter A General rules of electrical installation design

F42
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F - Protection against electric shock
a b
In
In1
Fig. F75 : Residual current circuit-breakers (RCCBs)
In
In1 In2 In3 In4
Choice of characteristics of a residual-current circuit-breaker
(RCCB - IEC 61008)
Rated current
The rated current of a RCCB is chosen according to the maximum sustained load
current it will carry.
b If the RCCB is connected in series with, and downstream of a circuit-breaker, the
rated current of both items will be the same, i.e. Ιn u Ιn1 (1) (see Fig. F75a)
b If the RCCB is located upstream of a group of circuits, protected by circuitbreakers,
as shown in Figure F75b, then the RCCB rated current will be given by:
Ιn u ku x ks (Ιn1 + Ιn2 + Ιn3 + Ιn4)
Circuit-breaker and RCCB association – maxi Ιsc (r.m.s) value in kA
Electrodynamic withstand requirements
Protection against short-circuits must be provided by an upstream SCPD (Short-
Circuit Protective Device) but it is considered that where the RCCB is located in the
same distribution box (complying with the appropriate standards) as the downstream
circuit-breakers (or fuses), the short-circuit protection afforded by these (outgoingcircuit)
SCPDs is an adequate alternative. Coordination between the RCCB and the
SCPDs is necessary, and manufacturers generally provide tables associating RCCBs
and circuit-breakers or fuses (see Fig. F76).
Upstream circuit-breaker DT40 DT40N C60N C60H C60L C120N C120H NG125N NG125H
Downstream 2P I 20A 6.5 6.5 6.5 6.5 6.5 3 4.5 4.5 4.5
RCCB 230V IN-A 40A 6 10 20 30 30 10 10 15 15
IN-A 63A 6 10 20 30 30 10 10 15 15
I 100A 15 15 15 15
4P I 20A 4.5 4.5 4.5 4.5 4.5 2 3 3 3
400V IN-A 40A 6 10 10 15 15 7 7 15 15
IN-A 63A 6 10 10 15 15 7 7 15 15
NG 125NA 10 16 25 50
Fuses and RCCB association – maxi Ιsc (r.m.s) value in kA
gG upstream fuse 20A 63A 100A 125A
Downstream 2P I 20A 8
RCCB 230V IN-A 40A 30 20
IN-A 63A 30 20
I 100A 6
4P I 20A 8
400V IN-A 40A 30 20
IN-A 63A 30 20
NG 125NA 50
Fig. F76 : Typical manufacturers coordination table for RCCBs, circuit-breakers, and fuses (Merlin Gerin products)
8 Residual current devices (RCDs)
Schneider Electric - Electrical installation guide 2008