Nightmare Garage Electrics, any advice?

[gbrown100]

Hi

Just moved into a new house with a detached (by 3 metres) garage. The electrics in the garage are fed via 2 core underground steel stranded cable but had no separate fuse box, no earth rod etc. I ripped it out as I fitted a new light as the old one didn;t work and that stopped working after the second time I turned it on. So:

1. The feed seems to come from a ring feeding the kitchen off a 30amp fuse - I assume this should be on a separate fuse? Is this dangerous otherwise?

2. There is no earthing rod in the garage and there is no earth in the armoured. Is it possible they used the steel as the earth? Is this a bad thing to do?

I want to re-use this cable later to supply a consumer unit with 16amp MCB for a couple of sockets and 6amp MCB for a couple of strip lights. What is your advice, rip it out and start again? If so, what should I be running, 3 core armoured with earth from the house or 2 core and an earth rod in the garage.

Thanks for any help you can give.

Graham

 

[pdcelec]

Is it a TNS TNCS or TT supply?

 

[andy]

Hi

Just moved into a new house with a detached (by 3 metres) garage. The electrics in the garage are fed via 2 core underground steel stranded cable but had no separate fuse box, no earth rod etc. I ripped it out as I fitted a new light as the old one didn;t work and that stopped working after the second time I turned it on. So:

1. The feed seems to come from a ring feeding the kitchen off a 30amp fuse - I assume this should be on a separate fuse? Is this dangerous otherwise?

2. There is no earthing rod in the garage and there is no earth in the armoured. Is it possible they used the steel as the earth? Is this a bad thing to do?

I want to re-use this cable later to supply a consumer unit with 16amp MCB for a couple of sockets and 6amp MCB for a couple of strip lights. What is your advice, rip it out and start again? If so, what should I be running, 3 core armoured with earth from the house or 2 core and an earth rod in the garage.

Thanks for any help you can give.

Graham

1: unless its fed thru an FCU (i.e a spur) then it can be dangerous

2: er... the steel IS the earth. also you can use 1 of the cores if ther eis a spare...

ideally, you should have it on its own radial, using a 32A MCB and 2C 4mm (possibly 6, depending on length) SWA feeding into a mini-CU.

and what earthing arrangements do you have?

 

[gbrown100]

Is it a TNS TNCS or TT supply?

I'm no electrician so I looked this up. I believe it is TNCS, (SUPPLY>FUSE>METER>FUSEBOX)

1: unless its fed thru an FCU (i.e a spur) then it can be dangerous

2: er... the steel IS the earth. also you can use 1 of the cores if ther eis a spare...

ideally, you should have it on its own radial, using a 32A MCB and 2C 4mm (possibly 6, depending on length) SWA feeding into a mini-CU.

and what earthing arrangements do you have?

1. It is spurred off of the ring, I cannot find where this has been done, likely behind a cupboard or something.
2. I wasn't sure if you could use the steel as the main earth running to/from the house and garage.

As for earthing arrangements - I think the setup I ripped out was relying on the steel in the armour to supply earth for the garage from the house. Certainly I only have a 2 core armoured cable and there is no other earthing point in the garage!

Basically, I bought the CU and 16amp + 6 amp MCB's for the garage. When I found there was no earth that stopped me since I do not know enough to be confident about earthing an outbuilding. I really need to know whether I should be earthing the garage separately, using the steel in the armour for the garage earth or running a new cable and bring the earth from the house (it is only 3 metres away).

 

[Adam_151]

some clarification is neccessary I think,

There are three ways in which earths can be supplied:

1) TNS, the supplier runs three core cable, or two core with a metal sheath (think of the SWA you spoke of) to your house to give your live, neutral and earth, neutral and earth are one and the same at the substation, but separated after.

2) TNC-S, The supplier runs two core cable, or two separate single core cables to your house, earth is derived from neutral in the meter cabinet, but separated after that. Requires that the neutral has high integrity and is tied to physical earth only its length. Popular with suppliers atm. Has special considerations to take into account when wireing outbuildings.

3) TT, The supplier runs two core cable, or two separate single core cables to your house, and doesn't bother giving you an earth, earth is provided by a rod in the ground, you need rcd protection to protect agaisnt phase-earth faults, the suppliers are replaceing this with TNC-S where possible.

Think lec has posted pics to illustrate this in the sticky at the top of the electrical forum.

 

[gbrown100]

Thanks for the clarification Adam_151. Indeed the electrics are TNS then as I have Live, Neutral and Earth coming from the supply cable. The Neutral and Live go to the supplier Fuse, meter then the domestic fuse box and the earth goes straight to my domestic fuse box.

So now as before the question of how I should supply an earth to my garage remains. Should I:-

1. Be using a feed coming from a 32amp MCB on my domestic board via the existing 2 core armoured and installing a new earth in the garage?

2. Be using a feed coming from a 32amp MCB on my domestic board via the existing 2 core armoured and using the earth from the house via the steel armour in the cable.

3. Be using a feed coming from a 32amp MCB on my domestic board via a newly layed 3 core armoured cable and using the earth from the house via the third core?

One last thing. What is the best way for me to test whether the earth connection is good in the current armoured cable. I cannot get to the part where it is spurred from the Kitchen ring so cannot verify by simply looking! The only testing equipment I have access to is one of the plug in testers for a 13 amp socket that has LED indicators of different types of wiring faults. Could I just connect a socket at the end of the armoured and test that?

 

[gbrown100]

FYI

1: unless its fed thru an FCU (i.e a spur) then it can be dangerous

Andrew2022 - The spur is taken from the kitchen ring but to my knowledge it is not connected to an SFCU until in the garage (unless it is hidden somewhere!). Presumably this SFCU should be at the point it is spurred from the kitchen not at the other end...

I think I really need to find where the hell this feed comes from. I plan to have the house rewired and therefore the garage put on its own radial off of an MCB of its own but this is a little way off as yet. For now I wanted to safely get power back in the garage without a massive overhaul!

 

[Adam_151]

Personnally I'd rip it out (switch off the ring, diconnect swa at garage end, terminate in some kind of end box, ring back on, disconnect swa at source when you are able to, but no rush), install 3 core SWA, 6mm² should be suffienct on a 32A breaker (4mm² would probably do as well, would have to go and look it up), but you might want to install thicker for future proofing

Use a core on the SWA as earth, but earth the steel wire as well, use brown as live, put blue sleeve on grey and use as neutral, and put earth sleeve on black and use as earth.

Does the garage cu have an rcd, if not, then you will have to come off the rcd side of the house cu

 

[Qedelec]

Testing

Do not rely on the plug in neon tester alone. These can be good for spotting incorrectly wired sockets, but are useless at determining if you have adequate earthing.
Use a loop tester to measure the resistance of Phase-substation-cpc. Your safety and those of your family are in your hands.

 

[gbrown100]

There is no RCD, only a double pole isolater. Should I have an RCD as well, is this better. I guess I can take it back and exchange is with one with an RCD.

 

[gbrown100]

Indeed the outcome of this is that for now it is not worth attempting this until I have a decent CU installed in the house. Either at the same time or Once that is up and running I will get the feed to the garage. You'll see another post on that subject coming up