TT system with kmf

Mpenhallurick · Jun 27, 2016

Hi, just looking for someone to confirm my plan is correct for a new installation, power is coming into the building from a 25mm2 single core SWA with armour as the neutral, that goes through 80A main fuse then through the meter. As the earthing is system, would I then need to run tails through an rcd, then through the KMF before heading into the consumer unit through 3 core SWA, if this is all correct. Would my earth from the SWA connect straight onto the earth rod or would it have to go to somewhere else first.

dont do much domestic work so just wanted to clarify this was correct before carrying out work, many thanks

Darkwood · Jun 27, 2016

Welcome to the forum

Risteard · Jun 27, 2016

You don't get single core SWA for very good reason. (It's AWA.)

I presume you mean a concentric cable.

Mpenhallurick · Jun 27, 2016

Sorry AWA. I'm just concerned about what protection I need in the meter box. I'm prettt sure what I've said is correct I just wanted to make sure.

Pete999 · Jun 27, 2016

What's "all relevant" mean, only asking because if you are a trainee it may be best if you apply for access to the Trainee section, being blase about your qualification doesn't really help us to tailor a response to your question. A sketch of your plans would help as well.

Richard Burns · Jun 27, 2016

If you mean that you have a supply coming in where the supplier has not provided an earth and you need to install a TT earthing arrangement then all circuits will need protection by a residual current device unless you have a sufficiently low R[SUB]A[/SUB] to allow an MCB / fuse protected arrangement.
Since that level of is not easily obtainable it is very likely that you will need to protect the distribution circuit from the meter to the CU with an RCD to ensure that the distribution circuit will disconnect on an earth fault.
So long as the SWA is connected to the earthing system of the installation then the location of that connection will not be critical but it is likely that you will want to provide an MET close to the origin and connect the SWA to that MET.