Electrical contractor information

Supply Characteristics and Earthing Arrangements

The following typical characteristics are applicable to residential and light commercial/industrial premises for low voltage supplies up to 630 amps. You may find these useful when completing BS 7671 Electrical Installation Certificates.

Nominal Voltage U/Uo = 400/230v
Nominal frequency f = 50 Hz
Prospective fault current Ipt: 25kA (3 phase), 16kA (1 phase)
External loop impedance Ze:
0.35 ohms typical maximum for TNCS system
0.8 ohms typical maximum for TNS system
The Ze values may be higher on older networks and should be verified by measurement.

Supply Protective Device Characteristics

Type BS1361: up to 100 amps
BS88 part 5: 200 amps and above

Nominal current rating
100 amps maximum residential single and three phase
100, 200, 315, 400 and 630 amp - industrial /commercial