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Use of galvanized steel pipe for electrical supply to building

wpqs

I am renovating my house. Regulations BS7671 apply though my house is not in UK.

The building's electrical supply is provided by three phase cables running externally and fixed to brackets at the top of the building. My local electricity provider has asked me install:

  1. trunking running down the face of the building to a junction box at ground level
  2. a galvanized steel pipe (sleeve) running underground  from the junction box to the meter which will be located in the under-stairs cupboard next to the main distribution board

I propose putting the steel pipe in the concrete slab next to my neighbor's party wall. This will avoid the need to perforate the new damp proof membrane / course as the pipe enters/exits the ground.

Does BS7671 allow such a galvanized steel pipe? Are there better alternatives? What advice would you give about the steel pipe or trunking.

thanks in advance

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    Provided the cable inside the pipe is insulated and sheathed (i.e. can be deemed to provide protection from electric shock by means of double/reinforced insulation) then technically the pipe won't be an exposed-conductive-part and so there's no need for the pipe to be Earthed on that score. In some places around the world it's common to see lengths of straight steel conduit used in lieu of cable clips.  Being underground it may well additionally need a surrounding earth/c.p.c. (and some upstream means of ADS) but if the cable is armoured or concentric construction that requirement could be satisfied by the cable itself so again no need to specifically Earth the pipe. If it's running underground and then exposed inside the installation it may well need to be main bonded (but the size calculation for that is quite different to that for a c.p.c.).

    If you have a TT Earthing arrangement I'd be very wary of allowing the pipe to be an exposed-conductive-part and connecting it to the consumer's earthing system unless the supplier provides and upstream RCD (as EdF do in France) - a fault would make the entire earthing system permanently hazardous live.

         - Andy.

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  • 0

    Provided the cable inside the pipe is insulated and sheathed (i.e. can be deemed to provide protection from electric shock by means of double/reinforced insulation) then technically the pipe won't be an exposed-conductive-part and so there's no need for the pipe to be Earthed on that score. In some places around the world it's common to see lengths of straight steel conduit used in lieu of cable clips.  Being underground it may well additionally need a surrounding earth/c.p.c. (and some upstream means of ADS) but if the cable is armoured or concentric construction that requirement could be satisfied by the cable itself so again no need to specifically Earth the pipe. If it's running underground and then exposed inside the installation it may well need to be main bonded (but the size calculation for that is quite different to that for a c.p.c.).

    If you have a TT Earthing arrangement I'd be very wary of allowing the pipe to be an exposed-conductive-part and connecting it to the consumer's earthing system unless the supplier provides and upstream RCD (as EdF do in France) - a fault would make the entire earthing system permanently hazardous live.

         - Andy.

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