Summer house

farqu01 · Apr 15, 2021

Hi, looking for suggestions or indeed what you guys do when wiring in SWA to plastic house CUs.

gland swa to a Metal JB then connect from JB to CU?

Fit sub main like the wylex fused isolator using 25mm meter tails via henley blocks to keep supply out of house CU rcds?

fit gland plate/nut to plastic CU then.fit glanded cable to this then earth gland plate to cu earth bar? Use breaker on rcd side?

its a 30 meter run 10mm 3core SWA spare 40 and 45 amp breaker available in CU.

Just looking for ideas of what you guys do, cheers

pc1966 · Apr 15, 2021

Your details say "DIY" but in Scotland, so the Part P building requirements don't apply. The forum rules don't allow for advice that might be dangerous/illegal to follow, but you seem to be asking sane questions. Can you clarify your electrical skill/experience?

In terms of the actual question, it kind of depends on the use of the summer house and how much trouble power loss would cause. If you have a spare 40A MCB slot then it is easy to feed a small CU and feed sockets, lights, etc, but you will have poor selectivity between MCB/MCB(RCBO) due to both having the "instant" magnetic trip.

With SWA you could feed it via a fused-switch, sized as high as the SWA fault-clearing Zs will allow to get good selectivity, but ideally also 1.6 times smaller then the DNO fuse to ensure total selectivity with that. For example, if you have a 63A DNO fuse then a sub-main on 63/1.6 = 40A (closest) fuse cannot blow your DNO fuse no matter what.

But doing so means splitting your house CU tails, and that means you either have an isolator already or will need the DNO to pull the fuse to allow the work to take place.

For the SWA gland it can go in to plastic, but you need to use the banjo or an "Earthing nut" to properly bond the armour to the MET to allow fault clearing, even if 3 core so it has the CPC inside.

Unless you have some real experience in doing this I would say you should get in a professional. You see what the details are, discuss your options, and if acceptable do the cable install (or duct, so you can also run network cable along side it, etc) yourself.

Soi disant · Apr 15, 2021

pc1966 said:
Your details say "DIY" but in Scotland, so the Part P building requirements don't apply.

No, but it's common sense to do things properly and safely - Scottish volts are as dangerous as English ones.

pc1966 said:
The forum rules don't allow for advice that might be dangerous/illegal to follow, but you seem to be asking sane questions.

My first thought was that he's asking questions which aren't related either/ors -

farqu01 said:
gland swa to a Metal JB then connect from JB to CU?

Fit sub main like the wylex fused isolator using 25mm meter tails via henley blocks to keep supply out of house CU rcds?

Are not two different ways to "wire SWA to plastic house CUs".

pc1966 said:
Can you clarify your electrical skill/experience?

Good question - I'm concerned that he's picked up a few terms here and there but doesn't truly understand them. Can't help thinking that anybody really competent to do this work would know whether he wanted the summer house fed from the CU or not.

Then there's the T-word....

pc1966 said:
Unless you have some real experience in doing this I would say you should get in a professional. You see what the details are, discuss your options, and if acceptable do the cable install (or duct, so you can also run network cable along side it, etc) yourself.

farqu01 · Apr 16, 2021

Hi, thanks for the feed back.

Yes I come from an electrical back ground, mainly industrial, oil rigs/platforms. Mainly maintenance on LV/HVelectrical systems, power generation and instrumentation
Have done plenty of SWA glanding into motors,switchboards and various other apperatus etc.
Perhaps I did not word my original post in a coherant way. I do apologise for that, I did not expect to criticised for seeking information.

PC1966 has answered my question and I am going for the banjo. I just wanted to be 100% that this was fine to do.I thank you for that.

I will of course be more down with the lingo if I have further questions, after all this is what forums are for or atleast what I though they were for.

Have a nice day

Soi disant · Apr 16, 2021

It wasn't criticism, or point-scoring, or anything like that - just genuine concern about your knowledge and competence.

farqu01 · Apr 16, 2021

Oh right, thats ok then.
I'll be fine to do this work thanks for your concern x

pc1966 · Apr 16, 2021

I should add that if glanding to plastic you are much better to use an Earthing nut / piranha nut (instead of traditional banjo) as they lock to the threads and retain a good contact / no loosening without too high a compressive force for the plastic. These sort of things:

Earthing Nut 20mm 2 Pack - Screwfix

Order online at Screwfix.com. FREE next day delivery available, free collection in 1 minute.

www.screwfix.com

Just need a ring crimp terminal for the fixing screw to wire transition. Personally I would connect both ends (armour to CPC core/earth terminal) even if you would be OK for fault clearing on the armour alone (i.e. R1 + R2 of armour is enough to meet Zs when attached just at the source, not needing parallel CPC to bring down Rs at the load end), just gives that extra path for safety.

farqu01 · Apr 16, 2021

pc1966 said:
I should add that if glanding to plastic you are much better to use an Earthing nut / piranha nut (instead of traditional banjo) as they lock to the threads and retain a good contact / no loosening without too high a compressive force for the plastic. These sort of things:

Earthing Nut 20mm 2 Pack - Screwfix

Order online at Screwfix.com. FREE next day delivery available, free collection in 1 minute.

www.screwfix.com

Just need a ring crimp terminal for the fixing screw to wire transition. Personally I would connect both ends (armour to CPC core/earth terminal) even if you would be OK for fault clearing on the armour alone (i.e. R1 + R2 of armour is enough to meet Zs when attached just at the source, not needing parallel CPC to bring down Rs at the load end), just gives that extra path for safety.