Outdoor Electrics

Rusty2 · 9 Apr 2006

Hi - just a few quick questions - in running electrics to new shed I plan to use 2.5mm cable from RCD side of split load consumer unit and a 32amp MCB to a waterproof junction box on house wall. From this I will run SWA cable to shed and place small consumer unit in shed for power and lighting. My questions are these:
1) Is it sufficient to run from RCD side of slplit load consumer unit or do I need to put in a separate RCD for this run?
2) If I need an RCD for the actual run itself, I assume this should be before the run goes outside the house where it could potential get w

et, rathe than in the shed itself?
3) When connecting the SWA, should the armnour be connected to the earth as well as the earth cable inside?
Many thanks, Russ

RF Lighting · 10 Apr 2006

Hi Russ,
A 2.5mm2 cable should not be connected to a 32A MCB. It should either be a 6.0MM2 cable or connected to a 16A MCB. Connecting to the RCD side of your CCU is fine, but if there should be a problem with the wiring or an appliance in you garage it will cause all the protected circuits in your house to loose power, so it might be worth connecting the feed to the non-RCD side of your CCU and fitting an RCD in the garage CCU. The armouring of the SWA must be connected to earth as well as the earth wire in the SWA. Remember this work will have to be notified to LABC under part P of the building regs.

Rob

Rusty2 · 10 Apr 2006

Many Thanks Rob - think I will do as you suggest and place a wall mounted RCD in garage - presumably this does need to be fitted before the run goes outside?
With reference to the cable - is this because it will only be a radial rather than a ring, so it will have only half the capacity?
Chhers, Russ

dingbat · 10 Apr 2006

Rusty, take the SWA cable into the house and mount a metal adaptable box (or, even better, a threaded conduit box) next to the consumer unit so you can terminate and earth the armour. Strip back the armour a couple of feet but leave the inner insulating sheath intact, so that now you have a decent length of double-insulated conductors to take into the consumer unit itself. Don't forget to take an earth conductor from the box to the earth terminal.

At the other end, use a metalclad RCD consumer unit and gland the SWA straight into that.

The size of cable depends on the intended load, the rating of the protective device and the length of run (among other things). You really need to get this right before you start digging that trench.

ban-all-sheds · 10 Apr 2006

Rusty - before you go any further, do some more planning after you've read this:

http://www.tlc-direct.co.uk/Book/4.3.1.htm

and this:

http://www.tlc-direct.co.uk/Book/5.1.1.htm

and this:

http://www.tlc-direct.co.uk/Book/6.1.1.htm

and this:

http://www.tlc-direct.co.uk/Book/7.13.1.htm

and this:

http://www.tlc-direct.co.uk/Book/7.14.1.htm

Also this: http://www.iee.org/Publish/WireRegs...matters_electrical_installations_outdoors.pdf in case it applies to you.

Buying a copy of the On-Site Guide would also be a good idea.

dean023 · 10 Apr 2006

If your garage is remote to the dwelling it SHOULD be connected to the RCD side as it's outside the equipotenial zone

ban-all-sheds · 10 Apr 2006

No it's not.

If you export the earth, then by definition it is within the equipotential zone....

dean023 · 10 Apr 2006

ban-all-sheds said:
No it's not.

If you export the earth, then by definition it is within the equipotential zone....[/quote

If the garage is remote then I don't see it any different to a shed and I personally think the supply cable should be RCD protected. But i'll check the standings on this.

ban-all-sheds · 10 Apr 2006

I'm not a fan of protecting the cable, as it puts the RCD remote from the outbuilding, which is a nuisance, and it puts the outbuilding lights on the RCD, which could be dangerous.

And if you decide to use a time-delayed 100mA RCD at the supply end to avoid those two problems, then I start to wonder what the value of an RCD with a time delay is in terms of protection of a cable with an earthed armour....

dean023 · 10 Apr 2006

I know where your coming from, I just thought from a regulation point of view that you had to (but i may be wrong) i'm sure that if it's remote you do but if adjoined you don't but i might be talking B@ll0cks! and i apologies if I am

comms · 10 Apr 2006

If you are going to use a metal clad cu in the shed and swa to feed it & your supply is of the TT type you will have to install an rcd to the supplying cable upstream of the metal clad cu & swa armour, so personally I'd put the swa supply to the rcd side of the board. Thats as I've said if the system you have is TT.
Hope that makes sense to you all if your interested.

ban-all-sheds · 11 Apr 2006

comms said:
If you are going to use a metal clad cu in the shed and swa to feed it & your supply is of the TT type you will have to install an rcd to the supplying cable upstream of the metal clad cu & swa armour,

A better answer would be to terminate the SWA in an insulated enclosure...

so personally I'd put the swa supply to the rcd side of the board.

So not only an RCD at the house, but one that takes out the house as well...

dingbat · 11 Apr 2006

As B-a-n has said there is no requirement to RCD-protect the supply cable.

To do so introduces the possibility of nuisance tripping if the RCD employed happens to be the one which also looks after circuits in the house.

If you use a separate RCD at source you would need to return to the source to reset it, which is both a nuisance and a potential hazard (exiting shed in the dark, stumbling down dark path, etc...)

If you have an RCD at each end you need to provide discrimination... which comes at a price.

But this wheel has been invented before: Provide the cable with overcurrent protection and stick your RCD at the business end.

Like electricians do.

Rusty2 · 11 Apr 2006

Many Thanks for all replies - looks like the best policy will be to run cable and put RCD in shed.
What does it mean, by the way, to provide the cable with overcurrent protection - is this the same as SWA?

Thanks again everyone so far! :

dingbat · 11 Apr 2006

Rusty2 said:
What does it mean, by the way, to provide the cable with overcurrent protection...

To prevent the cable from being electrically overloaded (overcurrent) you use a fuse or a circuit breaker of a rating below that of the cable's current carrying capacity.

But, of course, you'd know that if you'd done your homework!

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