The missing nuance

[John Rumm]

If electrics are your thing, read on; else there be boring stuff to follow!

Following on from the thread on SWA carrying two circuits, and in particular the issues raised concerning the actual armour resistivity rather than just its adiabatic fault withstand capability; I have updated:

a new table that includes the armour resistance to facilitate calculations of earth loop, or equivalence for the purposes of a bonding conductor. I added 5 core SWA for completeness.

I have temporarily retired the table for 70 deg C PVC clad cable since I did not have data for the armour resistance, and the cable seems less commonly available anyway - anyone know of a source of figures? I suppose we could estimate them based on the total armour area....

I have also explicitly broken out:

reworded it a bit to attempt clarification of the bonding conductor requirements.

See if that makes any more sense. Feel free to edit comment as appropriate.

[neverwas]

> and reworded it a bit to attempt clarification of the bonding

A question rather than a comment.

We have at present a TN-S supply. (Old lead sheath cable.) Neighbours with more recent fuses and meters seem to have been converted to TN-C-S (and that is certainly the norm on new builds locally). Is this something they do as a matter of course, and can they insist on doing so despite the knock-on consequences for exported earths or whatever?

It's not a wholly theoretical question as I'll need to get our meter upgraded to 100A when we get a new kitchen and I *may* one day get around to building a shed and using something other than a 20m extension reel.

[Andy Wade]

Yes, if the service cable has to be replaced for any reason you'll find that the only earth offered is TN-C-S/PME. You always have the TT option of course, but in normal circumstances I'd upgrade the main bonding if necessary and accept PME for the house.