Existing Power to Garage.

[RyanM]

My friend has a new house, with power to it....and really it's not too safe.

It's fed from the main Consumer Unit off a 15A trip with no RCD, in 2.5mm T+E.

This goes in to a double socket, and everything else is spurred off this socket, which includes another double socket, two separate outside lights, two internal lights, but one light is spurred from the other light. Then the final spur is an electric garage door. There are no fuses or trips in there, other than the 15A MCB in the house.

Now, a few little questions......

1). Does the RCD have to be in the consumer unit, or can it go in the garage?

2). Will it be best to have 3 separate MCB's in the garage. One to feed the lights, another to feed the sockets, and another to feed the garage door on it's own circuit?

3). As it's a garage (although no 'garage' work gets done in there), will it be best running everything in conduit?

4). The existing cable from the house to the garage: It comes out from the house, in to a piece of plasic conduit, for around a meter, across a gap. Then it's clipped the full length of the garage.
Is it ok using this existing cable? As it would be impossible to put a new one it, as there is a new kitchen, tiling etc where it runs.



I will be installing everything, then getting a certified electrician to sign it off etc. He is a friend and recommended this as he is too busy to do the installation, but he will check and test it etc afterwards.



Thanks

 

[rebuke]

Are you sure it's 15A - I've not seen a 15A MCB before, only 16A ones. You normally only see 15A rewireable fuses...

1) It depends on the route of the cable from the CU to the garage, if it is e.g. buried at less than 50mm in a wall (not in earthed metal conduit etc) then the cable must be RCD protected, so the RCD would have to go in the house CU.

2) It doesn't hugely matter, you could have a mini CU in the garage, or you could just use fused spurs, either would be equally acceptable.

3) It would probably be a good idea, but not specifically required

4) I take it by 'across a gap' you mean the conduit is suspended in some way outside the house - how wide is the gap, and how is it supported (and is any T&E exposed to the sun outside?)

If it were me, then depending on the route the 2.5mm cable has been run, assuming the derating factors don't mean it doesn't have the capacity, I would upgrade the MCB in the house to 20A, and then just put two FCUs in the garage, one for the lights (with a 5A fuse in), and one for the garage door (with an appropriate fuse for the load, no idea what a garage door motor needs). That way you have a fairly straight forward radial circuit...

Note that officially a certified electrician cannot sign off someone elses work under Part P - while there are those willing to do it, note that they are strictly speaking breaking the law.

 

[RyanM]

Hi, thank you for your reply.

I did mean 16A sorry, my fat fingers got in the way of me typing!


1). As I or the new owner of the house isn't sure at what depth etc it is buried at, I think it's safe to say it needs a RCD in the house then really! Although they are getting the CU changed to one with RCD's fitted, so I suppose this solves that problem.

4). Yeah, it's suspended in the sense it is slightly poked in to the house brickwork, then across a 1m gap (ish), this is then clipped to the wall. The cable then comes out, and is clipped to the side of the garage. It is exposed to sunlight, although it has been painted over.

Pic to show it easier:

I didn't realise that about the part-p to be honest. I'm sure my friend does though

 

[rebuke]

Don't have the OSG / copy of the regs in front of me, but I'm fairly sure that that wouldn't count as adequate support for the conduit.

I'm also fairly sure that the T&E shouldn't be run outside like that, I've been told that it doesn't have UV protection, so will break down gradually in the sun, but I'm sure someone else will be able to give a more thorough answer.

One solution might be to put a waterproof junction box on the wall where the cable appears, and junction in to SWA. You could then suspend that across the gap on a catenary wire, and run it round the edge etc. It could then run into the garage and junction back into T&E or a mini CU or whatever...

 

[RyanM]

Yeah, I thought the cable might have to be changed to be honest....


Is it within the regs to use a waterproof junction box? As this would work quite well for me I think.

I could also take the cable in to the gargae, at the wall nearest the house to reduce the run, and exposed area etc

 

[ericmark]

1). Does the RCD have to be in the consumer unit, or can it go in the garage?

May seem odd way to put it but it goes before what it protects so if the cable house to garage needs protecting then must go in house but if garage supplied with SWA then one may fit in garage. But on saying that one must also consider volt drop under fault conditions and in the garage one may want to fit an active rather than passive type.

2). Will it be best to have 3 separate MCB's in the garage. One to feed the lights, another to feed the sockets, and another to feed the garage door on it's own circuit?

If whole supply is only 16A then all that is really required is a FCU (fused connection unit) for lights and maybe a junction box.

3). As it's a garage (although no 'garage' work gets done in there), will it be best running everything in conduit?

SWA (steel wire armoured) cables is easier than conduit and most domestic garages have twin and earth you could go half way and use Ali-tube cable.

4). The existing cable from the house to the garage: It comes out from the house, in to a piece of plasic conduit, for around a meter, across a gap. Then it's clipped the full length of the garage.
Is it ok using this existing cable? As it would be impossible to put a new one it, as there is a new kitchen, tiling etc where it runs.

An assessment needs to be made as to if it is likely to get damaged either physically or through sun light cables outside are normally black there is no hard and fast rule.

I will be installing everything, then getting a certified electrician to sign it off etc. He is a friend and recommended this as he is too busy to do the installation, but he will check and test it etc afterwards.

You have it wrong way around FIRST you get the electrician to agree to what work he is happy for you to complete. Then you install to his design and allow him to monitor at agreed stages otherwise he will not be allowed to sign an installation certificate for work he has done or overseen. There are some rules as to having work registered and inspected but being as England is between us I have not gone into the rules but believe they are stricter than the Part P we have controlling us.

 

[ericmark]

I nearly made same mistake as Rebuke as far as I am aware Location: Stirlingshire, United Kingdom means Scotland and Part P does not apply in Scotland they have their own regulations and as I said I have not really studied them but believe they are more strict than Part P.
I started my reply before the others were visible.

 

[rebuke]

Oops, yes, my bad - forgot to check location. No Part P in Scotland, so ignore those bits of my post...