Waveform neutral

Question

Two relatively long 300mm2 3-core Waveform cables in ducts below ground supplying an industrial building. Currently the cables belong to the DNO but the contractor has permission to adopt them into a new proposed 1MVA PV/battery arrangement if he so wishes. The conductors are configured as three lines in parallel, outer copper wire screen in one cable as neutral and earth in the other. 
 Its not a good start with the reduced neutral and plenty of machine control in the plant but no issues apparent. Parameters for normal design procedure are not yet clarified as everything is at an early stage but I was just wondering about the BS7671 perspective. I have never used the cable as it is generally for DNO application. The cable cannot be touched at any point other than at both ends.

gkenyon · Answer

lyledunn said: but I was just wondering about the BS7671 perspective. 
 Lyle, I thought you'd be all over this one. Here's my take on how it could be viewed (hopefully not in a Court): 
 Not permitted by BS 7671, not safe at the very least for maintainers, possible breach of legislation ... and nothing to do with the protective conductor which is a more tenuous argument. A neutral that is not a PEN conductor (i.e. in a TN-S system, or a TN-C-S system downstream of the "separation") is a live conductor and is required to be insulated. The sheath of this cable is not insulation. 
 Regulation 131.2.1 is the fundamental principle. Regulations 411.1, Sections 416 and 417 are the primary Part 4 protection for safety) references. 
 Regulation 7 of EAWR 1989 is of course the legislation in question that may be breached, along with, possibly, Designer's Duties under CDM Regulations (safe maintenance if only skilled or instructed persons have access to touch the Neutral, otherwise, safety for all employees in a place of work).

Waveform neutral

Join us to get the best from IET EngX.

Community Rules & Guidelines