Changes are coming, what do you all think

[Wilko]

Hi J, IIUC with an upfront RCD (same position as TT case) the RCD would sense current in L and not N as it's now going back through the rod. And so it'd trip. We would still need a rod (at the PME terminals in your pic) but now we just use it to disconnect the installation rather than put in many rods and try to keep touch voltages down.

 

[1Justin]

But it's not fault current, it's any residual installation neutral return current which is able to lift the MET and all exposed conductive parts. The neutral current is surely still balanced in the tails since it's got to be the same as any live current. (There is no earth fault in the installation during this condition to make it otherwise)

 

[Wilko]

I think I get you now - the "upfront RCD" would have to be on the DNO side of the PME connection to work.

 

[Deleted member 26818]

I think I get you now - the "upfront RCD" would have to be on the DNO side of the PME connection to work.

The RCD would be best placed after the DNO PME connection. It would then also operate in the event of an installation Earth fault.

 

[Sparkingmad]

I can see the logic in it to be honest IET have produced guidance notes on this before but NICEIC inspectors would give you a berating for having 2 different earthing arrangements . So when you are asked for earthing arrangement at origin what would you put down TNCS, TT or will there be a new classification code TNCS/TT?
Would you have to install a rcd on tails from the meter before they enter an AMD 3 board rated at 30mA, or would you be able to install an rcd with upto 1A tripping current as it is for a dribution circuit on a TT system? Could you decide to ignore the TT side of it and continue as for TNCS as the TT part would only come into play when DNO lose neutral on their network. I don’t mind as I am on a trusty old TNS supply at the moment lol.