Advice on safety of existing garage wiring

KKen · 11 Aug 2010

Hi,

I found this forum after researching into the possibilty of adding another socket to the existing wiring in my garage. After reading the posts and advice, I'm now worried about the existing wiring, never mind adding anything new!

Here's a very crude drawing of the existing setup:

Untitled

KKen
11 Aug 2010
2

This was installed with the house, new build 10 years ago. Initially, I though all was well but I've found the following "features" which seem a little concerning:

1) The connection to the garage is a spur from the ring final, not a radial circuit from the house CU as I expected.
2) The spur from the ring final is standard 2.5mm unprotected cable through the cavity to an outside connection box. It doesn't travel directly into the back of the connection box but comes in from underneath. Is this normal?
3) By having the garage CU split the lighting and sockets, does this not constitute a spur off a spur?
4) Again at the FCU, is this not a spur off a spur (... off a spur!)

I'd like to add another double socket at the front of the garage and was planning to spur this off the existing double. However it would appear I have more spurs than Clint Eastwood!

My thoughts are that the garage should be fed from a new MCB in the house CU. However the only spare slot is marked "B G J W D"?

NB: Both house and garage CU have RCD devices in them. I'd be tempted to add the additional socket myself but wiring an additional MCB would be a job for a sparky.

Any advice on the safety of the existing setup?

Regards,

Ken.

MalcofArabia · 11 Aug 2010

KKen what you have there is not legal you can not run a garage installation off of ring final circuit spur.

You never quoted what size the SWA is or how far it runs. Those pieces of information is vital if your not to dig up the existing cable.

If it's 2.5mm then you will need to replace it. If it's 4mm and not to far a run then you should be ok. 6mm should cover most anything.

What a sparks will do for you is disconnect that spur immediately. After all that entire garage installation is on a 2.5mm spur and your only allowed 1 extra socket of an individual spur, not as you have many sockets and lights.

He will then if you have a spare way run a new supply from your CU to that junction box and terminate there.

Now you could do this yourself providing you will inform you local building Authority. That will cost you well over a 100 pounds just to do that. Then the Local Authority may insist on a test done by a qualified sparks and that will now cost you!! or the best route is get a qualified Sparks.

If i list a few things that you will need to do then you can see why

1 is the exisitng SWA big enough
2 What size cable is needed from the CU to outside box
3 Is the outside box suitable for the enviroment
4 Earthing arrangement for the garage in some case you may have to make it a totally different system ie TT if you can't export the earth
5. Is your exisitng installation man enough to really have those extra ligfhts and sockets

I could go on mate but in all honesty a days work for a sparks it's all done and you have no problems as it will be certified as well

MalcofArabia · 11 Aug 2010

Sorry KKen I should also have said that in order to use the exisitng SWA you will need to carry out a small Periodic Inspection Report (PIR) on it and the garage to satisfy that the installation is safe.

A Sparks will check and make sure that the cable and everything is safe so this is just to highlight more that really you should get a Sparks in

holmslaw · 11 Aug 2010

KKen · 11 Aug 2010

MalcofArabia said:
KKen what you have there is not legal you can not run a garage installation off of ring final circuit spur.

1 is the exisitng SWA big enough
I haven't measured it but it looks significantly more chunky than the 2.5mm cable feeding it! I'd say around 20-25mm outside diameter.
2 What size cable is needed from the CU to outside box
?
3 Is the outside box suitable for the enviroment
It would appear to be a suitable weatherproof box.
4 Earthing arrangement for the garage in some case you may have to make it a totally different system ie TT if you can't export the earth
I think it has an exported earth AND a separate TT.
5. Is your exisitng installation man enough to really have those extra ligfhts and sockets
Probably not!

You've confirmed my concerns. At least part of it (the SWA and garage CU) look professional. I just can't believe it's configured as a spur!

My thoughts are to employ a sparks to connect a new wire from the CU to the existing junction box and test the onward connections. How easy is it to run a wire from the CU without removing all the plasterboard?

SWA goes into the ground from the junction box (depth unknown) and reappears inside the garage, which is indeed warm and dry all year round.

Ta for the help,

Ken.

MalcofArabia · 11 Aug 2010

I don't think you would have both a exported Earth and a TT System as that don't make sense, but stranger things have happened.

You may find that you can drill through the wall your CU is on, providing it's an out side wall and most of the work could be done externally.

A good sparks will know the best way to do it and 90% of us will not ill advise you. The old adage of getting 3 quotes is sound. But make sure you write down exactly what you want and give a copy to each that way you and the contractor will both know what you want and price accordingly

KKen · 11 Aug 2010

MalcofArabia said:
I don't think you would have both a exported Earth and a TT System as that don't make sense, but stranger things have happened.

You may find that you can drill through the wall your CU is on, providing it's an out side wall and most of the work could be done externally.

A good sparks will know the best way to do it and 90% of us will not ill advise you. The old adage of getting 3 quotes is sound. But make sure you write down exactly what you want and give a copy to each that way you and the contractor will both know what you want and price accordingly

Just checked, SWA earth connected to house ring final AND a separate earth wire comes out of the garage CU and goes through the wall and into the ground. Bizarre.

Garage CU has the same stylised initials scrawled on it as the house CU ("dFh"). I'd like to meet Mr/Mrs dFH to ask what they'd been smoking that day.

Will get some quotes to get is sorted properly, thanks!

Ken

ELZ4742 · 11 Aug 2010

KKen said:
MalcofArabia said:

I don't think you would have both a exported Earth and a TT System as that don't make sense, but stranger things have happened.

You may find that you can drill through the wall your CU is on, providing it's an out side wall and most of the work could be done externally.

A good sparks will know the best way to do it and 90% of us will not ill advise you. The old adage of getting 3 quotes is sound. But make sure you write down exactly what you want and give a copy to each that way you and the contractor will both know what you want and price accordingly

Click to expand...

Just checked, SWA earth connected to house ring final AND a separate earth wire comes out of the garage CU and goes through the wall and into the ground. Bizarre.

Garage CU has the same stylised initials scrawled on it as the house CU ("dFh"). I'd like to meet Mr/Mrs dFH to ask what they'd been smoking that day.

Will get some quotes to get is sorted properly, thanks!

Ken

at one point, a garage/outhouse/building which was more than a certain distance from the house (cant remember how far) had a seperate stake.
the incoming cable was earthed at the house, and not connected in the outhouse. a seperate stake was used for the outhouse supply.

as i can recall, it was done this way for nuisance tripping.

SUNRAY · 12 Aug 2010

On a local housing development the garage is being powered exactly like this using 4mm T&E and armoured.

plugwash · 12 Aug 2010

Any advice on the safety of the existing setup?

As it stands the wiring is not compliant with BS7671 but as long as the run lenghths aren't horriblly long (to put it technically as long as Zs is in spec) and the cable is at least 2.5mm^2 it's IMO safe. The MCBs in the garage CU will provide overload protection for the spur from the ring.

Just how long are the runs? where do they run? and what size cable is in use?

plugwash · 12 Aug 2010

MalcofArabia said:
KKen what you have there is not legal you can not run a garage installation off of ring final circuit spur.

On what grounds do you claim it's not legal? It's not compliant with BS7671 but BS7671 is NOT law.

Part P (which hadn't come into force when this work was done) only requires "Reasonable provision shall be made in the design and installation of electrical installations in order to protect persons operating, maintaining or altering the installations from fire or injury.". IMO provided the Zs is in spec and the cable is at least 2.5mm^2 this installation does meet that.

SUNRAY · 12 Aug 2010

plugwash said:
MalcofArabia said:

KKen what you have there is not legal you can not run a garage installation off of ring final circuit spur.

Click to expand...

On what grounds do you claim it's not legal? It's not compliant with BS7671 but BS7671 is NOT law.

Part P (which hadn't come into force when this work was done) only requires "Reasonable provision shall be made in the design and installation of electrical installations in order to protect persons operating, maintaining or altering the installations from fire or injury.". IMO provided the Zs is in spec and the cable is at least 2.5mm^2 this installation does meet that.

This does not comply with regs as only one spur from any point on a ring final is permitted, the garage is surely considered as 2 spurs, protected with 6A & 16A MCB's respectively.

This system is still being installed on at least one local housing development albeit using 4mm.

plugwash · 13 Aug 2010

SUNRAY said:
This does not comply with regs as only one spur from any point on a ring final is permitted, the garage is surely considered as 2 spurs, protected with 6A & 16A MCB's respectively.

Assuming by regs you mean BS7671 I'd agree with you.

But not compliant with BS7671 is not the same as unsafe or illegal.

SUNRAY · 13 Aug 2010

plugwash said:
SUNRAY said:

This does not comply with regs as only one spur from any point on a ring final is permitted, the garage is surely considered as 2 spurs, protected with 6A & 16A MCB's respectively.

Click to expand...

Assuming by regs you mean BS7671 I'd agree with you.

But not compliant with BS7671 is not the same as unsafe or illegal.

Oh yes but at 22A its getting very close to the rating of the cable if its 2.5mm depending on length etc

skenk · 13 Aug 2010

There's less than 1A of lighting connected at the moment and all the sockets except the freezer are fed from a fused spur so assuming that is not overloaded the maximum demand will be around 15A. I agree it needs sorting out (new cable from CU to JB/garage depending on SWA size as others have said...) but it's not necessarily unsafe at present. If it is 2.5mm SWA then a 20A breaker could be used (dependent on length etc..)

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Advice on safety of existing garage wiring

holmslaw

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