Is this SWA wiring suitable/safe and can it be added to???

[freddieab]

Hi everyone,

I have been looking over this site for some time but there so many conflicting and varied setups I felt I needed to post my own question. I have tried to include as much relevant detail as I think is required from reading other posts and would like to thank you in advance for any replies and advice.

I have not long moved into a new house and the previous owner had done a lot of work electrically in the garden for a workshop and a pond.

I would like to have a couple of external sockets and lights added to the existing setup but I am not sure that the existing setup is necessarily suitable or safe.

I have attached a drawing of how it is laid out below.

The setup is as follows.

T&E from non protected side of CU in house from a B20 to a 30mA 80Amp RCD.

From here I believe it is 6mm 2 core SWA out of the house 5m to a small cupboard.

In the cupboard is a metal junction box from which 2.5mm T&E runs to 3 double sockets.

The SWA continues from the junction box out of the cupboard to a shed at the bottom of the garden about 30m away. The cable is buried except for in the cupboard and shed.

In the shed the SWA terminates in a CU with a 30mA 40Amp RCCD.

From this CU 1.5mm T&E runs radial to a light and 2.5mm T&E runs in a ring to several sockets. These run from fuses in the CU. B6 and B16 respectively.

My questions are firstly is this suitable/safe and secondly would I be able to have external lights, 2, and external sockets fitted to the shed?

Also would I be able to spur of the junction box in the cupboard 3m and have a similar setup to the cupboard in another cupboard?

Again thanks in advance for any advice.

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• freddieab
• 14 Apr 2008
• 2

 

[electronicsuk]

It's a bit of an odd setup but for the most part sounds safe, if you're correct about all the breaker ratings and conductor sizes then the B20 breaker in the house sounds sensible.

If there is adequate space in the JB then spurring off with another length of 2.5mmsq T+E shouldn't be a major problem as everything is behind the 20A breaker, although the lights will obviously need to be fused down further by whatever method you choose. Before starting any work it may also be worth investigating the earthing arrangements in the existing installation a little further.

 

[RF Lighting]

Is your earthing type a TT supply? (See here for explanation)


The only thing I don't like is the fact that you have two RCDs of the same rating in series. This does not provide discrimination between the devices in a fault condition.

 

[SparkyMarky]

I'm no expert on garden electrics, but I'm intrigued by the earthing arrangement. The furthest shed appears to be a self contained TT installation with it's own spike, but I can't see the earthing arrangement on the other shed. Presumably it connects to the earth spike in either the house or the furthest shed (or both?) using the armour of the SWA?

 

[securespark]

Is the majority of the run in 6mm²?

If the majority is 2.5mm² & you have a B20 protecting it, the Volt Drop is too high.

 

[freddieab]

Hi,

Thanks for the quick replies.

I have added the following pics to hopefully show it clearer.

The 2.5mm from the B20 to the RCD in the house is maybe 12" max. RCD is top left.

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• freddieab
• 15 Apr 2008
• 1

I cant locate any earth in the first shed.

Could I spur SWA from the metal junction box underground about 3m and have a similar set up with the sockets at the end?

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• freddieab
• 15 Apr 2008
• 1

Not sure which earthing system my house uses but maybe someone can tell from the pics. The earth wire on the far left goes out through the wall and into the ground outside.

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• freddieab
• 15 Apr 2008
• 1

Thanks again for the advice.

 

[freddieab]

Actually the earth wire on the far left does not go into the ground outside. It bonds onto the gas pipe that runs along the side of the house.

 

[streetlighter]

Looks like the SWA going into the RCD unit has not been fitted with a BW gland and they have used a BS951 earth clamp not the best way of earthting the armour as it will compress the cores inside the cable.
Is it 2-core or 3-core SWA ?

 

[freddieab]

Looks like the SWA going into the RCD unit has not been fitted with a BW gland and they have used a BS951 earth clamp not the best way of earthting the armour as it will compress the cores inside the cable.
Is it 2-core or 3-core SWA ?

Hi, it is 2 core SWA.

 

[streetlighter]

Then i would advise the use of a proper BW20 gland at the house end.

 

[Steve]

Open that metal JB in the shed. If theres no earth to those sockets, you are at risk of death.

Its all a bit . . . . messy.

Here's what I'd do:

Move the CU and earth rod (get it checked) to the first shed, from the second. (In fact, buy a new CU without an RCD)

Replace the JB in the first shed with the CU. Have 2 circuits. Sockets in the first shed, and sockets in the second shed.

Feed the lights in shed 2 with a 5A FCU.

Run all the sockets as 20A radials.

Also, make sure the second run of SWA has sufficiently low resistance for the earth supply to the second shed.

 

[freddieab]

Thanks for the advice Steve.

I have looked in the junction box and the T&E earth is screwed to the back plate of the metal junction box. Is this sufficient?

The jist of what I understand is that I need to have a gland fitted to the RCD in the house.

Im not sure I follow what you say about the CU in the first shed.

Would this be a CU, without an RCD, into which the two SWA ends that are currently in the JB would run along with an earthing spike connected to it?

What about the second shed? This is 30m from the first so a radial to the sockets from the first would not work. Would the existing CU remain in there with the earth spike and RCD?

Thanks again for the advice. Not going to do any of this myself, just trying to weigh up if anything needs doing or not as it just looked a bit rough and ready.