SWA into plastic cu

longers30 · Apr 18, 2014

Hi guys just finishing off a rewire where I have a 6mm 3 core SWA Sub main running to an outbuilding. I'm connecting into a 10 way plastic cu in the house which is going to be positioned just under the ceiling in the hallway with the cable dropping down from above into it. Just wondered on the best way to connect the SWA I've heard people mention earthing nuts but never come across them. It is a T-N-CS earthing arrangement and is going on a 40a MCB, non RCD, protected running to a metal clad board in the outbuilding with the 3rd core used as the cpc and armour connected on the supply end. Any advice would be appreciated

Simon-0116 · Apr 18, 2014

box

100 x 100 plastic or galv box, gland off into that then into board

trev · Apr 18, 2014

Gland the swa into the CU, where you fit the banjo drill through and drop a bolt into the hole. After you fit washers and a nut or 2 crimp a lug onto an appropriately sized fly lead and take that to the earth bar with the third core.
Btw, if you're fitting a CU up against a ceiling you need a rethink.

trev · Apr 18, 2014

Re: box

Simon-0116 said:
100 x 100 plastic or galv box, gland off into that then into board

Why complicate things?

davesparks · Apr 18, 2014

You will need to earth the armour properly at the other end too as the gland in to the metal board there will give a partial connection even if you don't intend it to.
At the supply end I would probably gland it into a galv through box and then bush that to the CU. That gives you good mechanical fixing of the SWA to prevent it bending your CU out of shape and a handy earth terminal to bond the armour.

If you search for pirannah earthing nuts you will see what you have been missing out on there.

Hawk81 · Apr 18, 2014

Or gland into the board and use 1 of these

Octopus · Apr 18, 2014

Hawk81 said:
Or gland into the board and use 1 of these

Could be tricky doing anything like this if the board is that close to the ceiling with the cable coming down!

longers30 · Apr 18, 2014

Yeah the cu has to go up against the ceiling really it's pretty tight for space and it's where all the cut-out and meter are so the owner wants it all boxed in when it's done.

longers30 · Apr 18, 2014

Yeah this is the problem with the position of the board. I may have to consider placing a box as suggested to the side of the cu, gland into that and take the cores through the side. Any thoughts on this?

Hawkmoon · Apr 18, 2014

If you are installing a 6mm swa (I take it there is nothing extraneous in the 'outbuilding' ?) then it shouldn't stress the CU if you cleat appropriately - I would go with Trev's idea since it's in a hall and appearance may be an issue.

Engineer54 · Apr 18, 2014

As Hawkmoon has indicated if the supply is PME/TNC-S and this outbuilding has any extraneous metalwork/pipes etc, then a 6mm 3 core isn't going to crack it. It's then going to be either a 10mm 3 core, or running in a separate 10mm earthing conductor alongside the 6mm SWA...

HandySparks · Apr 18, 2014

longers30 said:
Yeah this is the problem with the position of the board. I may have to consider placing a box as suggested to the side of the cu, gland into that and take the cores through the side. Any thoughts on this?

Yes, I go with this option. Either a galv adaptable box or a right angle galv conduit box. Either would give a solid connection and look neat.

longers30 · Apr 18, 2014

There are no extraneous metal parts in the outbuilding just some lighting and power.

longers30 · Apr 18, 2014

So am I right in saying that with these earthing nuts you gland the cable as normal and the earthing but just goes over the thread and is held with the grub screws? Then a fly lead from this to the MET?

Richard Burns · Apr 18, 2014

longers30 said:
So am I right in saying that with these earthing nuts you gland the cable as normal and the earthing but just goes over the thread and is held with the grub screws? Then a fly lead from this to the MET?

Yes you just replace the banjo and retaining nut with the piranha nut.
The grub screw prevents the nut from loosening and the screw holds a ring terminal for the earth fly lead.