Most of the info I've found shows the gas and water pipes connected to the main earthing terminal (MET) via 10mm2 cables. My gas and water pipe earth bond cables are connected back to the consumer-unit earth bus bar with 10mm2 cables and the bus bar is then connected to the MET via a 16mm2 cable. Is that within the regs?
I hope so, or I have been doing it wrong for years.
That sounds ok.
Using the CU earth bus bar as a main earthing terminal is quite common - especially on smaller installations. 16mm^2 is probably more than adequate (in the absence of any specific instructions from the supplier).
AIUI it's fine to use the consumer unit bar as the MET, and then run an unbroken bonding conductor to the supplier's incoming earth and/or earth rod, OR have a separate MET.
It's not supposed to be gas-CU-MET-supply, as that means there's a break between the gas and the MET. In short, there can only be one MET per installation?
But that's only a suggestion, I wouldn't dare contradict Adam.
(I do a lot of electricians, or quietly tidy up behind them when they're gone.)
Owain
Some DNO's require 25mm2 tails for PME connections (new or altered connections)
Yes, having read around a bit more I think you're right. The overriding principle is that the supplier's earth MUST go to a MET without any intermediate breaks/connections. So, if your supplier's earth is long enough to reach your CU then you can connect it directly to the CU earth bus bar and it then becomes the MET. But, as in my case, if the supplier's earth is a short tail, so that of necessity has to be connected to a small local earth block, then that earth block is now the MET and the earth bonds to the gas and water pipes must go directly from that and not from the CU.
It all gets a bit confused in an installation like ours, the supply incomer is in the garage and there's company fuse, meter and a main switch there but the CU is in the house 20 or more yards away. It's not really realistic to have unbroken bonding from the gas and water pipes (in the 'standard' under the sink location in the kitchen) to any sort of company provided MET.
Well there's "not really realistic" and there's inconvenient. Your situation is certainly inconvenient from an installation standpoint but it's definitely not unrealistic. Certainly if it were a new installation it would have to meet the condition that the main earth cable between supplier's earth and the earth block from which the gas and water bonding is taken, which is the MET, has to be unbroken. But I'm not an electrician and I do wonder how an electrician would in practice actually install such a circuit. A catenary between garage and house with suitable cable perhaps?
No, it doesnt. The Earthing Conductor, from the Distributors Earth goes to the Main Earthing Terminal. This can be in the consumer unit, or a separate earth connector block. Then a suitable size cable from the MET to either the Consumer unit, or another earth block. The Main Protective Bonding Conductors can then be connected to either. Think of the many houses that have a PME supply, with a MET in the meter cupboard outside. Running bonding cables to that would be very difficult a lot of the time. What about flats? The MET would be at the Incomer downstairs, you are 10 flights up, would you run, if needed, a cable down those 10 floors? Of course not, you'd connect it at your local consumer unit.
Depends on the fuse size.
+1 (a perfect answer IMHO)
Yes, good point.
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