Advice on Garage Electrics

[mottsy]

Hi Again,

Just after some reassurance.

My detached garage appears to be a spur from the house ring main. It operates via the ring main MCB. (I do not know where on the ring the spur is taken from, (No FCU’s visible) but it travels underground to the garage where it goes into a garage consumer unit.

The garage CU has two MCB’s one for the lighting and one for the sockets. The lighting consists of, 1 x fluorescent, 2 x 60w bulbs and an outdoor PIR activated light with a 60w bulb.
There are three single sockets that power a freezer, dehumidifier (operates 4hrs a night on a timer) and a battery charger to keep the caravan battery topped up. Occasionally we might plug in a vacuum cleaner to do the car.

I am intending to replace the sockets with RCD sockets but having read other posts that a garage should be on its own circuit, wondered if mine is safe?
I am not worried about it not meeting current regs as it was all done years ago and to fit it on a separate circuit would involve lots of channelling inside the house & digging up concrete driveways etc outside.
All the wiring in the garage appears in good order, it is not rubber covered and is protected in proper trunking. There have been no known problems caused in the past, (No MCB’s tripping etc.)

I know that you guys can not give a definite answer just from a description but what are your thoughts? Does it sound OK if not ideal or should I start digging up the drive and getting the bolster chisel out?

Your views will be greatly appreciated.

 

[dingbat]

I am intending to replace the sockets with RCD sockets but having read other posts that a garage should be on its own circuit, wondered if mine is safe?

The only way to know if yours is safe is to have it properly inspected and tested. But a good way of making it safer is to have those sockets RCD protected. If you don't already have RCD protection from your main consumer unit then replacing with S[ocket]RCDs is a step in the right direction.

 

[Dellsmp]

Does the garage cu contain an rcd?
If not just put one in there and alls ok.
If the house sockets are on an rcd and there is no spurious tripping then all is probably ok and best left alone.
When all said and done there is nothing better than getting it inspected and tested, as dingbat said.

 

[mottsy]

Thanks for the replies.

the garage CU was a wired fuse type but has had the fuses replace with MCB so no RCD is fitted to this. The same applies to the house CU.

As the freezer is running in th garage I thought that socket RCD's fitted to both sockets not supplying the freezer and probably a switched fused connection unit for the freezer, would be best. (I certainly feel confident enogh to do these simple tasks myself.)

Anyway thanks for the replies my main concern was that being a spur off the house ring main would in some way mean it was dangerous.

Regards

Mottsy

 

[Adam_151]

Anyway thanks for the replies my main concern was that being a spur off the house ring main would in some way mean it was dangerous.

You should cerainly try and find it, it should be a fused spur, if its not, there is the possibility over overloading the spur cable depending on its size, and if its connected towards the end of the ring, there is a possibility of pulling the full circuit load through it and overloading on side of the ring even if the spur cable is sized to handle 30A.

Logical places to start looking would be the back of sockets and inside the CU

 

[PompeySparks]

What type of cable enters and supplys the Garage CU? is it black & round (armoured)? Can you look at the cable's sheath and find the size of the conductors printed on there?

As others have said, a spur from the ring final is ok (so long as there is an RCD somewhere along the line - at the house DB, Garage DB or the Sockets) but it should be taken from a fused spur!

 

[mottsy]

Hi again.

The cable enters the garage from metal conduit that comes up through the garage floor. It is normal grey sheathed twin and earth. It then enters a wylex two way CU with B6 & B16 MCB's. (These have replaced the old wired fuses). The cable is 10mm wide and looking at the reference section, this equates to 2.5mm cable.

There is no RCD anyware at the moment. As mentioned I will be fitting RCD sockets. I was going to fit two RCD sockets and run the freezer from a FCU, but would I be better using a passive RCD for the freezer?

I have checked the walls behind the units in the kitchen to see if there are any signs of replastering, (The kitchen is closest to the garage so I assume it enters the house here), and can not see any. I will go and check the house sockets when I get a chance to try and trace the spur. (I assume a simple continuity test from the garage to socket is the best way to try and trace it. (With all the mains electric off of course.)

As I mentioned, I know by current standards this is not ideal but as long as it is not an obvious danger I will put up with it probably untill such time as I decorate the kitchen and find the spur. Once I find it I assume I need to get a fused spur fitted as mentioned in the earlier reply.

Thanks again for all the imput.

Mottsy.

 

[JohnD]

You can get a "garage" consumer unit very cheaply which includes an RCD as main switch, and an MCB for lights and sockets. This could replace your old Wylex CU and would be cheaper than buying a few RCD sockets (they are rather expensive). If the garage is fed of the downstairs ring you can isolate the supply from the house, so it is not as worrying as changing a house CU.

It seems a bit odd to have a garage sub-main fed from a spur. Usually a spur is taken from the back of a socket, but it can also be taken from the CU, on the same MCB as the ring. If you unscrew and look behind the socket face plates you wil probably find one with an extra T&E connected (I don't think a continuiy test will help unless you break the ring in at least two places).

There is a Wylex Retrofit RCD kit for the Standard CU, but this is quite expensive and IMHO no better or neater than a separate RCD. Your old Wylex is probably getting a bit long in the tooth by now. Though if you are doing anything more than replacing old sockets with new ones I suppose you ought to use a registered electrician.

Another very easy method (if you can find the source of the spur!) you can get a spur connection unit which combines an RCD with a fuse, in a single FCU sized fitting. This would be another cheap and simple way of doing it.

 

[mottsy]

Thanks John, I didn't realize that the spur could come from the CU.

I'll have to wait for the weekend to have a peak in the CU in daylight.

If it has been spured off of the ring main MCB, is this still OK or should I fork out for someone to fit a new CU in the house with RCD and plenty of spare fuseways as soon as possible. (Mine is only a 6 way and obviously they are all used.)
Also any idea of a ball park figure for fitting one? I live in the south near Reading. I know you cant give an exact figure but some indication of how much would be a great help.

If its not taken from the main CU, I shall look into this garage CU with RCD.

Many thanks

Mottsy.

 

[JohnD]

It's OK to take a single spur from the MCB at the CU. Never seemed to me to be worth doing, though, as you can spur just as easily off the nearest socket to the point of use.

If you've got plenty of money, a nice new, big, split load CU is nice to have.

But it is expensive - not because the CU is dear, or complex to fit, but because the installer will test (and possibly rectify) all the circuits which connect to it... which means your whole house. And it needs to be certificated, so is a surprisingly big job.

 

[mottsy]

Many thanks John,

I didn't realize a new CU was such a big job.

In view of this I shall probably get a new Garage CU with RCD fitted.

Which would you recommend?



http://www.screwfix.com/app/sfd/cat/pro.jsp?cId=A331827&ts=74613&id=63138

or

http://www.screwfix.com/app/sfd/cat/pro.jsp?cId=A331831&ts=74729&id=73324

or are ther any other better ones.

Thanks Again

Mottsy

 

[JohnD]

Personally I'd go for the plastic cased one, no chance of any of the conductors affecting the case if they come loose. It's also splash proof which might be handy if the roof should leak or you're carelesss with the hose when washing the car. I assume you are not going to be chucking bricks and hammers about in the garage and cracking the casing.

NB I am not in the trade, and you must now do a search on Part P in the Electrics UK forum, as you are due a lecture about the things you are not allowed to do yourself without getting a Building Inspector in.

 

[mottsy]

Thanks John,

While I'm confident at replacing switches and sockets, I've never had dealings with a CU so I think the yellow pages will be used.

Thanks again for all your advice.

Mottsy

 

[Adam_151]

I've never yet heard from anyone who doesn't think volex is a pile of crap, if you want plastic, there is a plastic cased MK one on the screwfix site,

the thing about conductors comming loose is a most likely a none issue, It'll be protected against indirect contact by the upstream overcurrent device in the case of a TN system, or in the case of TT by the upstream RCD. The exception is if the main supply is TN-C-S and the garage has been made TT, then there is no need for the submain to be RCD protected, but where the changeover point between the two systems is, it requires an RCD in a plastic case, however I doubt this is the case in your garage

 

[mottsy]

Thanks Adam,

The main house supply is TN-S. (Earth connected to the head of the main supply cables coming into the house). The garage is obviously earthed through this and it also has an earth connection from the Garage CU to metal pipework from a rising water main that supplies a cold tap in the garage. I guess that this would make it TT.
In view of this do I need an RCD fitted to the supply prior to it entering the submain?

Many thanks
Mottsy