10mm SWA into CU

[syl]

Is it possible to gland two 10mm2 SWA (3 core) cables directly to a metal garage consumer unit, something like this:

http://www.screwfix.com/p/wylex-2-way-garage-unit-63a-30ma-rcd/53927

If not, and I used an adaptable box directly beneath the unit, could I gland it in the box and then take the tails through into such a unit (would there be room for two lots of 10mm2 three core cable)? Or would I be better off joining them both to a single 10mm2 T&E cable in the box and take that to the CU?

If using a metal adaptable box, should I use a cheaper plastic CU? Alternatively should I just use a bigger metal CU (what size would be big enough to gland both SWA)?

(the first cable will be the supply in and the second will be the supply out to another shed)

 

[RF Lighting]

You should be able to easily get two 10.0mm² SWAs into that CU.

If you're glanding them into the top, I think one of the knockouts is either 32mm or 40mm, so you will need a reducing bush, and two lock nuts to allow your 25mm SWA gland to fit properly.

 

[Adam_151]

The knockouts in those M/c wylex units are pretty well stuck in and bash out from the inside IIRC. Therefore should be easy enough to drill a 25mm hole on centre, and once the gland is tightened the locknut and banjo tag will act as washers

 

[JohnW2]

The knockouts in those M/c wylex units are pretty well stuck in and bash out from the inside IIRC. Therefore should be easy enough to drill a 25mm hole on centre...

Every time I've thought that about an enclosure, the damned thing has popped out 'effortlessly' the moment I started drilling Mr Murphy's Law just can't be beaten!

Kind Regards, John

 

[SimonH2]

But to answer the second part of the OPs question ...
Yes, if you decided to terminate the SWA in an adaptable box. Just terminate the wire armour but leave the cores long enough to keep going out the other side of the box into the CU (bush the hole). Once the wire is off, then the inner is really just a rather stiff semi flexible cable.
You can strip the sheath back to leave separate cores as long as they are mechanically protected - particularly where they pass through the side of the box and CU. You'll want an extra earth tail off the SWA gland.

If you think about it, this isn't really much different to using singles in conduit and/or trunking.

 

[bernardgreen]

I find die cast boxes are easy to use and look better than adaptable boxes

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• bernardgreen
• 8 Mar 2009
• 10

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• bernardgreen
• 10 May 2009
• 17

 

[JohnW2]

Yes, if you decided to terminate the SWA in an adaptable box. Just terminate the wire armour but leave the cores long enough to keep going out the other side of the box into the CU (bush the hole). Once the wire is off, then the inner is really just a rather stiff semi flexible cable. You can strip the sheath back to leave separate cores as long as they are mechanically protected - particularly where they pass through the side of the box and CU. You'll want an extra earth tail off the SWA gland.

Indeed, but as the OP implied, in his case another option would be to join the conductors of the two SWAs within the adaptable box (with some sort of connector block) and take 10mm² T+E (or, probably better, 10mm² singles) from them into the CU - which might make things a bit easier/tidier within the (relatively small) CU.

Kind Regards, John

 

[ban-all-sheds]

Is it possible to gland two 10mm2 SWA (3 core) cables directly to a metal garage consumer unit, something like this:

http://www.screwfix.com/p/wylex-2-way-garage-unit-63a-30ma-rcd/53927

If not, and I used an adaptable box directly beneath the unit, could I gland it in the box and then take the tails through into such a unit (would there be room for two lots of 10mm2 three core cable)? Or would I be better off joining them both to a single 10mm2 T&E cable in the box and take that to the CU?

If using a metal adaptable box, should I use a cheaper plastic CU? Alternatively should I just use a bigger metal CU (what size would be big enough to gland both SWA)?

(the first cable will be the supply in and the second will be the supply out to another shed)

Do you plan to apply for Building Regulations approval for this work?

 

[syl]

No. I believe it's not notifiable since the recent changes to part P.

I will be employing an electrician to make a connection to the main consumer unit (new circuit, which is notifiable) but I will subsequently extend that new circuit myself.

 

[SimonH2]

Indeed, but as the OP implied, in his case another option would be to join the conductors of the two SWAs within the adaptable box (with some sort of connector block) and take 10mm² T+E (or, probably better, 10mm² singles) from them into the CU - which might make things a bit easier/tidier within the (relatively small) CU.

If you've stripped the SWA down to it's cores,then there's barely any difference - the L&N of the T&E will be near enough the same size as those of the SWA - only the earth will be a bit smaller.

No. I believe it's not notifiable since the recent changes to part P.

I will be employing an electrician to make a connection to the main consumer unit (new circuit, which is notifiable) but I will subsequently extend that new circuit myself.

Y'know, he seems to be onto something here.
The rules allow the installation of a CU (just not a replacement), and nothing qualifies as a circuit if there's no upstream OPD.

So diverging thread subtopic ... when the sparky comes along and connects the supply end of the SWA - what does he have to "sign off" ? Is it everything that's connected ?, or just the submain as far as the CU main switch ?, or something else ?

 

[ban-all-sheds]

I will be employing an electrician to make a connection to the main consumer unit (new circuit, which is notifiable) but I will subsequently extend that new circuit myself.

Have you already found one who is prepared to do this? i.e. certify on official documentation that he installed it, even though he did not?

And what next, for the outgoing SWA from the new CU to the next CU, or whatever it's serving, and any other new circuits from the new CU, and any other new circuits from whatever the outgoing SWA serves?

 

[ban-all-sheds]

Y'know, he seems to be onto something here.
The rules allow the installation of a CU (just not a replacement),

They do appear to have created that situation via the utterly inexplicable decision not to include two little words "or provision". Or to have used the word "installation" instead of "replacement".

However, they are absolutely sure that their intention was to make all installations of CUs notifiable, and currently they believe that they have because new circuits are.

and nothing qualifies as a circuit if there's no upstream OPD.

But there always is one, even if it's the service fuse.

 

[JohnW2]

Indeed, but as the OP implied, in his case another option would be to join the conductors of the two SWAs within the adaptable box (with some sort of connector block) and take 10mm² T+E (or, probably better, 10mm² singles) from them into the CU - which might make things a bit easier/tidier within the (relatively small) CU.

If you've stripped the SWA down to it's cores,then there's barely any difference - the L&N of the T&E will be near enough the same size as those of the SWA - only the earth will be a bit smaller.

It's not a matter of the size of the cores - it's the number of them. In other words, the choice is between taking two sets of SWA cores into the CU or just taking one set of cores (as T+E or singles) from a 'JB' into the CU.

Kind Regards, John

 

[JohnW2]

The rules allow the installation of a CU (just not a replacement),

They do appear to have created that situation via the utterly inexplicable decision not to include two little words "or provision". Or to have used the word "installation" instead of "replacement".

They certainly have created that situation. Your latter suggestion may have worked - although I can see problems with even that. Don't forget that pre-April there were any number of things that one could 'replace' without notification but whose 'installation' would require notification. I don't think your first suggestion would work - the CU might have been 'provided' by some third party!

However, they are absolutely sure that their intention was to make all installations of CUs notifiable, and currently they believe that they have because new circuits are.

They may be 'absolutely sure about their intention' but, as you know, whether they have achieved that intention (without 'catching' things they didn't 'intend' to catch) is a matter of debate/discussion.

Kind Regards, John

 

[ban-all-sheds]

It's not a matter of the size of the cores - it's the number of them. In other words, the choice is between taking two sets of SWA cores into the CU or just taking one set of cores (as T+E or singles) from a 'JB' into the CU.

Clearly the outgoing cable to the shed is a continuation of the incoming one, i.e. there's no submain from the garage CU to the shed CU.

So not only would I not try and make that joint inside the CU, I'd use a switch enclosure rather than a JB so that I could isolate the shed if I needed to without isolating the garage as well.