Good evening guys,
Just wondered what your thoughts are on the following:-
Big private house with many out-buildings.
Incomming supply is TT (no DNO earth provided) with a rod at the house and a MAIN varible RCD set at 500mA straight after the meter. Ra here is 27ohms. Idea of this RCD is to protect the installation before the metal containment starts.
Downstream in the main tails there are six switch-fuses after the RCD split out on tails from henley blocks. The six switch fuses feed underground sub-mains to vairous independant out-buildings in SWA. Each switch fuse has a 300mA type S RCD before it.
Currently each out-building has a rod but the earth core of all the sub-main SWAs are connected together aswell, so the six buildings earths and rods are all linked where the switch fuses all go back to the house MET.
I think this is a good setup as it actually brings the whole sites EFLI down to about 6 ohms, however I had a fellow electrician helping me today on this job of mine, he thinks this is wrong and that each building should be a complete TT island with no connection back to the MET of the house. I said I'd agree with this if it was an incomming PME supply, in which case we would bring the incomming earth to the outbuilding and then isolate it at that point with a rod taking over. However he would not have it, although he couldn't give me his actual technical reasoning for it being wrong.
Intersted in your thoughts!
