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https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl DIY Forum >> Electrical Questions >> Pattress conundrum https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl?num=1250116688 Message started by Trotty on Aug 12^th, 2009, 11:38pm

Title: Pattress conundrum
Post by Trotty on Aug 12^th, 2009, 11:38pm

Hello

From a spur in the house, via a fused RCD – I have an armoured cable running to an outbuilding. A gland is installed on the cable in this outbuilding. I'd planned to affix this gland to a flush mounted metal pattresss with a blank fascia (for access) inside the outbuilding. I'd then run cable from the pattress housing to a socket. Earthing is TN-S.

It has just occurred to me that the metal pattress that I had planned for the task will not be suitable to fix to the building's plasterboard. Can I use a plastic pattress? If so, where should the 'banjo' terminal be connected?

Many thanks

H

Title: Re: Pattress conundrum
Post by dingbat on Aug 13^th, 2009, 6:24am

Why not terminate directly into a metalclad socket?

http://www.tlc-direct.co.uk/Images/Products/size_3/MKK2977.JPG

Title: Re: Pattress conundrum
Post by Trotty on Aug 13^th, 2009, 12:36pm

Hmmm... I suppose I could - but this is going to be a garden room/living space and I know my missus would find the metal-clad socket a bit ugly.

I was wondering if it were some way to fix a flush-mount pattress or if a plastic one could be used...

Would it be sufficient to connect the SWA banjo tab to the SWA earth inside a plastic flush-fit pattress?

What value would either the metal pattress or metal-clad socket add in earthing terms?

Many thanks

Title: Re: Pattress conundrum
Post by Lectrician on Aug 13^th, 2009, 5:59pm

I dont think a dry liner type box would be considered strong enough to take a glanded cable.

Can't you fit the flush metal box to a noggin? If depth is the issue, place a noggin above and below the box and fix through the sides?

I would also terminate the SWA into a conduit coupler, and connect this to the metal box using a brash bush and serrated washer. You would not need to use a banjo. Are you using 3 core?

Also, why bother with a blank plate? Can you not terminate the SWA into the socket, or the first socket of the radial?

Title: Re: Pattress conundrum
Post by Trotty on Aug 13^th, 2009, 9:24pm

The noggin is a great idea – just what I was looking for (although I had to look up the term 'noggin'!).

I've already fitted the gland to the cable – so unless there's a good reason to use the conduit coupler idea – I think I'd rather leave it be. Is that OK?

I thought that the blank might be better for access and any possible future maintenance – but you're right – I guess that straight into the socket makes more sense and saves some unnecessary fiddling.

The SWA cable is 4 core but one core is unused.

So can I terminate the gland into the first metal socket and then connect the SWA earth, the SWA banjo to the earth terminal in the pattress?

Many thanks
Howard

Title: Re: Pattress conundrum
Post by Lectrician on Aug 14^th, 2009, 6:24am

The gland will take up a fair bit of space in a back box. This is why I suggest using a conduit coupler.

Even if you have already fitted the gland, the conduit coupler would simply be screwed tightly onto the end of it onto the 20mm thread in place of the locknut and banjo.

The brass bush and serated washer would then connect the coupler to the back box, the brass bush taking up to room at all.

Title: Re: Pattress conundrum
Post by Trotty on Aug 14^th, 2009, 7:37am

OK thanks. Is it correct that the armoured part of the SWA together with the earth core in the SWA and the pattress earth terminal should all be connected?

Title: Re: Pattress conundrum
Post by Lectrician on Aug 14^th, 2009, 7:59am

Yes.