Re: Question For Judd

Looking at that photo of the cut-out it could be a TN-S supply (separate neutral and earth) included in the incoming cable. The block on the top right of the cut-out is the connection for the incoming earth and there should be a 16*mm earth-wire running to that from the consumer unit.

If a sparky installed your new consumer unit for you, he should have left you a set of test results. The type of earthing should be written there.
There should also be earth-wires running from your gas and water pipes back to the consumer unit or a separate earth-block outside the CU.

Re: Question For Judd

Yes Judd, we were given a certificate of compliance, I'll dig it out and have a look. I'm glad I was channelling out into lightweight blockwork, at first, i cut in to take 25mm back boxes, but found that, on the single switched fused units, it was just to crowded with the double supply and load wires so, I have had to do more digging and fit 45mm boxes,

Re: Question For Judd

Judd, one final question, the spur that services the office will also extend to the Shed/Workshop (it has electrics previously serviced by a portable extension from the house) this will be isolatable by a passive fused spur within the Garage. The question is, is it Ok for this service to be run in standard 2.5mm T&E cable inside a suitable conduit, beneath the new lawn and, are there any connotations involved with the terminal socket being 33 metres from the consumer unit?

Re: Question For Judd

Sorry for the delay. Didn't see your question.

Because of the length of cable, I wouldn't be using 2.5mm T&E, I'd be using 2.5mm 3-core steel-wire-armoured cable used with the appropriate cable glands at either end. The s.w.a. would need to be terminated at either end in either metal conduit boxes, or steel switch/socket boxes (solid type, not the sort used to sink into walls). At the house end, I'd use a metallic (metalclad) switched fused spur so that the supply to the shed could be turned off. Use the armouring of the s.w.a. and the spare conductor within the cable as your earth which when used together in this fashion gives you an effective earth conductor size of around 6mm. To comply with regulations, this cable will need to be buried at least 18" into the ground to prevent damage from spades and garden forks etc. Alternatively, you could run this cable on the surface around the edges of the garden so that it can be seen and not be likely to get damaged. A bit more cable, but a damn-sight easier than sinking the cable into the ground.

I'm assuming that the shed won't be used for any heavy-duty appliances/machinery? The metalclad switch in the shed needs to be 5amp to restrict the load to around 1kW. The 5amp is necessary so that it blows before the 13amp fuse in the switched fused spur in the house.

By my calculations, the earth from the shed will be around 1.3 Ohms and will give you a fault current of around 195A

I presume that this also going to be protected by an RCD in the house?

Points to note: Because of the updated cable colours in the 3-core cable, there will be brown, black, and grey conductors. Grey should be used for the neutral and marked as such at either end with blue insulation tape, and the black conductor used as an earth. Both ends of conductor marked with green and yellow tape.

A quick tutorial on how to make a s.w.a. cable off.

https://www.youtube.com/watch?v=yPg74rD2j_s

Re: Question For Judd

Thanks for that Judd, and the tutorial, as you know, I never take the easy option, and will sink the cable. The present lawn is about four inches below its new finished height so I will dig down a foot or so for a distance of about 18 metres. Everything associated with this supply will be visible inside the garage so, subsequent owners of this property will be fully aware of the specification (and limitations) of the installation.