Bus duct - Earth cable Size

[charzree]

Bus duct is used to transmit the power from the secondary of the transformer to the Main distribution board? If the cable is used instead of bus duct, we would size the ground cable approximately half the cross section area of the power cables according BS 7671 table. 54.7

If this is a bus duct, how to decide the ground cable size? Noting that bus duct will have a metallic enclosure.

 

[Andy-1960]

Will the neutral be earthed at the transformer (TN-S) or at the L.V switchboard (TNC-S) ?

 

[davesparks]

If the cable is used instead of bus duct, we would size the ground cable approximately half the cross section area of the power cables according BS 7671 table. 54.7

Only if its a small size cable, or you want waste money on an oversize cable. For larger supplies we calculate the required size using the adiabatic equation from bs7671.

You should be able to carry out the same calculation for your bus duct system, or consult the manufacturers for further info.