Help with Shed Wiring

[madspark]

I recently purchased my first house and have decided to re-instate the electrical supply out to the shed. I’m a maintenance technician offshore so I’m not very familiar with the regulations required for domestic installations.

Anyway previously there was a supply running off a 16A MCB in the house consumer unit out to the garden shed (all this fed was some lights). For protection outside the 2.5mm twin and earth cable run through plastic conduit attached to the garden wall. I have completely dismantled this.

All I need the supply for is some sockets in the shed and lighting, there will be nothing major running off the supply.

I intend to run a 6mm twin and earth cable from a 40A MCB in the consumer unit in the house (this only has MCB’s), outside (buried underground) and into the shed which contains a smaller consumer unit (40A RCD supply). Off this there will be 3 sockets and 2 lights on separate circuits. The total length of the cable will be around 20m with 10m of this being outside

The main issues are:

Do I need to notify anyone about the installation even though it is replacing an existing supply?

What would be suitable for protecting the cable outside?

I was planning to bury the cable underground. I understand from the regulations that this has to be at least 450mm underground with electrical warning tape. What type of conduit would be suitable? Would it have to be metal or could I use flexible such as kopex?

Also a lot of the modern shed consumer units contain a 63A RCD as the incomer. I only have a spare 40A MCB in the house consumer unit. Does this mean that I would need to upgrade the house consumer unit to use one of the modern shed consumer units as 63A is greater than 40A.

 

[Dan]

@GMES can you help this guy?

 

[Darkwood]

Firstly forget the twin and earth idea, if you wish to bury a cable then use SWA, correctly terminated and earthed this would mean the SWA won't need RCD protection up front and can run off your existing system.
Are there any services in this shed IE gas and water and are they in metal?
Is the construction of the shed standard woodern hut or has it got steel supports running into the ground?
What is the supply type to the property (TNS, TNCS or TT) been the most common?

Your profile states electrical technician so its really just a brush up on the domestic requirements you're after here which shouldn't be a problem if you can answer a few questions

 

[GMES]

Regarding the Cable, I would run an Swa cable which won't need rcd protection and then Rcd the shed end.
twin n earth should be used indoors for internal wiring not external.

 

[GMES]

Queue jumper

 

[Dan]

Ta lads.

 

[madspark]

Thanks for the info!
It's an older house that I live in which has a TNS earthing system. I'm really disappointed by this a co-worker told me that it would be no problem to run twin and earth outside as long as it was protected mechanically in conduit so I went ahead and bought a 50meter roll of twin + earth last week. I don't think they were that bothered about the regulations.

So for future note does this mean that it is unacceptable to use twin and earth outside even if it is mechanically protected in something like conduit?

 

[madspark]

Also there is no services such as gas or water in the shed. It is just a old brick shed with a corrugated steel roof.

 

[ferg]

Technically T&E in earthed galv conduit is ok but in reality land where the rest of us live SWA glanded at both ends is the way to go.

In a perfect world swa in a duct.

The galv will degrade over time and the T&E will get wet and degrade also.

It is cheaper to use swa.

i

 

[GMES]

Thanks for the info!
It's an older house that I live in which has a TNS earthing system. I'm really disappointed by this a co-worker told me that it would be no problem to run twin and earth outside as long as it was protected mechanically in conduit so I went ahead and bought a 50meter roll of twin + earth last week. I don't think they were that bothered about the regulations.

So for future note does this mean that it is unacceptable to use twin and earth outside even if it is mechanically protected in something like conduit?

Technically your co-worker is correct about the mechanical protection but it's just bad design to use t&e as Ferg pointed out your conduit will degrade over time and then this will have a knock on effect to the cable.
Plus by the time you have bought the cable and Galv conduit, saddles, elbows etc etc , you could have bught the swa twice over.
Also with it being tns, it saves all the exporting pme drama.
So to clarify buy the right cable ( SWA ) connect into a mcb not rcd at the house end then terminate into an RCD board in the shed, As for the t&e use it to wire what you need in the shed. Nothing gets wasted then.

 

[GMES]

@madspark This is a quick guide that I had on the laptop to give you an idea of what Darkwood was talking about with different earthing systems.

 

[Spoon]

As for the t&e use it to wire what you need in the shed. Nothing gets wasted then.

To add to the above: Sell what is left over on Ebay or here on this forum.

 

[Taylortwocities]

For buried SWA, you are looking at a nice trench. Comme ca:

 

[madspark]

Thanks for you help!

I'm going to go down the SWA route as it will offer better protection. I have dug a trench around 400mm deep.

6mm 3 Core SWA Steel Wire Armoured Cable 30M BASEC Approved XLPE On DRUM - http://www.ebay.co.uk/itm/182194766409?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

Would that be a suitable cable to use? I've been advised to use 3-core. My consumer unit has a mixture of old and new cable colours.
With regards to the new colours what would be the best practice? I was thinking:

• Brown as live.
• Black as neutral with blue sleeving
• Grey as earth with yellow/green sleeving.

Does this sound acceptable?

 

[Spoon]

Seeing that you have a trench now you way want to consider putting a small cable duct into it, along with your SWA cable. Then you can put alarm (for shed door), Ethernet, phone cables in it, if they are needed.

 

[telectrix]

that cable is fine, but first check with a local wholesaler. most will cut whatever length you need and price per metre. i'd expect to pay £1.60/m +VAT. so his price is reasonable.

brown as live.grey with blue sleeve for N and black (sleeved Gn/Y) for cpc is the generally accepted practice, although not set in stone. the reason here is to dissassociate black from Neutral as it was with "real" colours.

 

[Taylortwocities]

And don't forget that the steel armour must also be connected to earth. Using a proper SWA gland, of course!
Here's how

 

[telectrix]

use CW20 glands, not the cheap BW version.

 

[Deleted member 26818]

The convention now is to use the grey as neutral, to disassociate black from neutral.
Should really sleeve or tape the correct colours near to the terminations.

 

[telectrix]

the term "new cable colours" is a misnomer in what is supposedly a technical and accurate industry. black and grey are both completely monochromatic and neither contain any colour whatsoever. they should be referred to as "new cable shades".