swa calculation

eamonn1983 · Jul 26, 2013

I need to work out if I will be required to run a separate protective conductor along side the swa cable I'm going to install. The cable is a sub mains feeding a 3 phase db panel in a large workshop. The cable is going to be a 50mm 4core 120 metres steel wire armoured installed in a underground duct. The protective device feeding the cable is a merlin gerin NS250N 160amp 3 phase mccb which and the readings at this end are zs 0.19 and pfc 1.23KA.

I'd be grateful if someone could tell me how I can determine if this needs a separate protective conductor and if so maybe explain the calculation,to help me,in the future.

Thanks in advance

telectrix · Jul 26, 2013

a chart was posted the other day by eng54, showing the armour sizes required to comply as cpc. generally, all SWA cables up to 95mm, the armour is sufficient as cpc. use forum search and you should find it.

telectrix · Jul 26, 2013

here post #155:

http://www.electriciansforums.co.uk...tions/23288-can-we-use-armour-swa-cpc-16.html

Engineer54 · Jul 26, 2013

eamonn1983 said:
I need to work out if I will be required to run a separate protective conductor along side the swa cable I'm going to install. The cable is a sub mains feeding a 3 phase db panel in a large workshop. The cable is going to be a 50mm 4core 120 metres steel wire armoured installed in a underground duct. The protective device feeding the cable is a merlin gerin NS250N 160amp 3 phase mccb which and the readings at this end are zs 0.19 and pfc 1.23KA.

I'd be grateful if someone could tell me how I can determine if this needs a separate protective conductor and if so maybe explain the calculation,to help me,in the future.

Thanks in advance

The table i posted and is being referred too, does not imply compliance for bonding purposes, however, if this large workshop already has it's bonding requirements catered for, from the supply that this sub-main is being taken from, it's all well and good. However, if it were a supply for a stand alone workshop with extraneous services etc, then a full size separate earthing conductor would need to be installed alongside the SWA cable, unless of course you used a 5 core cable, which aren't easy to come by...lol!!