Garage electrics

[Andypease1]

Hi All

Am revamping my garage electrics have installed a 4 way Consumer unit 2 x 6amp mcb ( lighting ) 1 x 16amp ( socket and garage door) 1 x 32amp (ring main 4 sockets and 1 spur.

Propose a 40 amp RCBO in my house consumer unit

Now for the cable no way to bury in the Tarmac drive so will have to put about
75mm down in the gravel strip that rounds around the house. Can use armoured or twin and earth both in plastic conduit . What is the requirement and should the cable be 4mm or 6mm2

Don,t worry wired my whole house then got it inspected. So will get the garage down when finished..

Cheers Andy

 

[flameport]

This has been done to death hundreds of times before, but in summary:

T&E can't used outside or underground.
Plastic conduit offers no protection for buried items and is therefore pointless.
SWA does not require additional conduit or anything else.
An RCBO in the house will be rather inconvenient as any fault in the garage will causea total loss of power in the garage and can only be reset from in the house.
It's exceptionally unlikely that this garage requires 2 lighting circuits, or a ring circuit for sockets, or a separate consumer unit of any size.
Cable size depends on load, installation method and length.
Inspecting after the event is not likely to happen in reality, and certainly isn't the correct way to comply with the law.

 

[Andypease1]

Thanks,

Its's a big garage and the circuit will have 4 double sockets on it. Lighting is split between inside and some security lighting on the walls outside.

There is emergency lighting in case of power failure

Main problem is how to get cable from house to garage as the drive is tarmaced so the strip of gravel around the house is the only option.

Cheers Andy

 

[JohnW2]

This has been done to death hundreds of times before, but in summary: ....

I think you probably forgot to include in your list/summary (with which I otherwise agree) that burying SWA (T&E having been discounted) only 75mm deep is far from being acceptable.

Kind Regards, John

 

[Andypease1]

I know it is unacceptable but I have no other options. The gravel strip around the house is about 125mm wide and is never disturbed and too close to house to walk on and why would anyone dig gravel.

Not sure what else to do except move

Cheers Andy

 

[JohnW2]

I know it is unacceptable but I have no other options. The gravel strip around the house is about 125mm wide and is never disturbed and too close to house to walk on and why would anyone dig gravel.

I can understand that view. All we can do is to tell you (which you probably already know) what the regulations require - and then it's up to you.

As you presumably realise, since the proposal is presumably a new circuit (from your CU), it is 'notifiable' work - and neither a LABC inspector (if you notify yourself) or a self-certifying electrician (if you employ one) would accept a cable buried as shallow as you are proposing.

Not sure what else to do except move

Without looking at the regs, I'm not sure whether a shallow-buried cable in earthed steel conduit would be acceptable - it might. SWA clipped to walls etc. would be acceptable, but there's probably not a route that would work. An overhead cable might be an option. Cheaper than moving house would be to hire a 'mole' (probably plus operator) to send the cable under your drive at an acceptable depth. Others may have other ideas.

Kind Regards, John

 

[sparkwright]

6.0 mm2 should be ok on a 40 amp RCBO. Don't use 4.0 mm2.

Always use SWA underground, don't use twin and earth.

Be sure to use cable glands properly, and be sure the armour is earthed.

 

[JohnW2]

Always use SWA underground, don't use twin and earth.

Yes, that's been said, as has the fact that SWA buried only 75mm deep is very non-compliant with regs. I'm separated from my regs at present - do you happen to know if 'shallow-buried' cable (probably SWA) in steel conduit would be compliant? - I'm not sure.

Kind Regards, John

 

[RF Lighting]

Don't have the RCD at the house end of the submains.

 

[EFLImpudence]

Why bury it in the gravel strip?

 

[JohnW2]

Why bury it in the gravel strip?

Do you mean rather than leaving it lying on the surface of the gravel? As for actual route, I think the OP has indicated that on/in/under the gravel strip is the only route which does not involve going under his tarmac drive.

As I've been asking, do you know whether cable in steel conduit buried only about 75mm deep would be compliant?

Kind Regards, John

 

[Andypease1]

Thanks guys

Will use 6mm with swa terminal glands

Why not have the RCBOin the house CU and I have emergency lighting in the garage And it will have a garage consumer unit. It means the cable is then well protected over it's length

This is the only route can clip to the wall under the gravel. To lay on top looks a mess and the gravel will give some extra protection. Overhead does not work either.

The distance is too far for a mole and you need to dig a pit at each end to get it in. New drive £10,000

Cheers

 

[sparkwright]

I do agree that with the RCD/RCBO in the house, at least the cable (and you really, really should use SWA) is protected.

The only problem with the RCD/RCBO in the house is that if there's a fault in the garage, it's a pain going into the house to re-set it.

It could be argued though that there are advantages to having the RCD/RCBO in the house. For instance, if there's a freezer in the garage, at least you can check easily that the RCD hasn't tripped.

But generally, the RCD goes in the garage, and SWA must feed it - as SWA offers far more protection than ordinary cable.

 

[Andypease1]

Will talk to the buiding inspector and see if he will grant a dispensation for running the swa in the gravel splash strip next to the house.

when I buildt the extension he gave me permsiion to use Wi FI smoke and co2 alarms with a remote alarm in the main bedroom than hard wired ones.

I think if he views the problem he will understand that what i am doing is very safe whcih really is what it is all about.

Cheers
Guys

 

[bernardgreen]

Could you not remove the gravel, dig down 450 mm. lay and bury the SWA, lay marker tape on the earth and then replace the gravel.

SWA 75mm below the surface is safe. but only as long as no one does any work that could damage the cable. You won't unless you forget the cable is there. Workmen or the next owner of the house may not be aware there is a cable that close to the surface.

If the outer cover of SWA is damaged by a spade then moisture can reach the steel armouring and over time the armour can rust away.