Earthing an SWA cable?

[newman]

What is the correct method for earthing an SWA cable in a insulated consumer unit?

Regards

[Christian McArdle]

Use a standard interior gland to terminate the cable. Replace the crap earthing tag and lock nut from the gland with a proper earth nut like a Piranha.

[Julian]

Are you using the armour as earth or a core? Both are OK AFAIK. If it's the armour then the gland kit should come with an earth lug - from there you wire with (10mm min?) earth wire to the earth bus. If using a core conductor then the answer is obvious! [1]

[1] Please not that I'm not an electrician so be prepared for a better answer!

[dcbwhaley]

But you should still earth the armour even if you are using a core as an earth.

[dcbwhaley]

But you should still earth the armour even if you are using a core as an earth.

[alexander.keys1]

I've used an earthing clamp, of the type used on water pipes, over the armour.

You could use a 'house service cutout' or a 'street lighting cutout' to terminate it neatly, and avoid disturbing the cable during alterations. The armour is pulled away from the inner PVC sheath, and bunched into an internal earth block. Make sure you get an 'SNE' type (Seperate Neutral and Earth).

[Tim S]

I wouldn't do that - the reaction force opposing the clamp is being provided by the insulation which is soft so it's not stable. Use the correct gland which clamps the wire between two bits of metal.

Good idea - and such boxes can be got in metal so the whole thing is a good solid termination.

Cheers

Tim

[Andrew Gabriel]

Yep, that's definately mis-use of an earthing clamp.

[alexander.keys1]

I've often seen them having been fitted to SNE lead-sheathed cables by the Electricity Boards, to provide a consumer's earth terminal. Seems to work OK.

[Andrew Gabriel]

The clamps I've seen electricity boards fit to lead sheathed cable are quite different -- more substantial brass jobs. I have seen other people fit standard pipe clamps, and crush the cable to a worrying degree.

A pipe clamp on the steel wire armour just isn't going to form a gas-tight corrosion resistant connection, because you're just going to squash the steel wires into the PVC inner sheath. A tiny bit of atmospheric moisture will cause the steel to rust and lose connection with the pipe clamp.

If, for some strange reason I can't think of at the moment, you really want a floating connection to the armour, use a proper SWA gland, with the back nut just being used to fix the earth tag to it.

[Andy Wade]

Sweated joints are also used by some DNOs, to attach an earth tail. BS

951 ("ordinary") earth clamps seem to have been used quite a lot in the past, but can work loose for the usual reason (lead creeps under load) and are now deprecated.

I should stress that only the DNO or their approved subcontractors should make or alter the earth connection to a supply cable sheath. Some of those old cables are quite fragile and there's a risk of causing a short and a very big bang if you mess with the cable. The next fuse upstream is typically 300 or 500 A. If you have a TN-S service and the earth connection to the cable is loose, get the DNO (REC or "board") out to fix it.

[newman]

I have no way of securing a gland to the CU as the cable is entering through a large cut-out at the rear of the CU.

Regards

[Christian McArdle]

Then you should terminate to an external junction box and run PVC from there.

Christian.