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Earth Bonding to CU or MET?

Postby Tim1 » Tue Sep 14, 2021 8:56 am

I'm having a PV system fitted.
The electrician has raised the following issue.

He said our oil & water 10mm earth bonding cables should go direct to the Main Earth Terminal, but ours go the CU Earth bar, then 16mm to the MET.
Is this is a must? They're not long enough at present. Although I believe, if we must, we could extend with crimps or soldering?
I can't find any definitive advice online.
Cheers, Tim
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Postby stoneyboy » Wed Sep 15, 2021 9:11 pm

Hi tim1
Your PV electrician is correct but is there any down side to your existing installation - probably not. Unfortunately the pve has to sign off the installation so he has the whip hand.
Regards S
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Postby Tim1 » Wed Sep 15, 2021 10:28 pm

Many thanks stoneyboy.
Now, the MET connects to an old, hopelessly undersized iron wire which connects to the incoming mains cable shroud. There's just a (new) single 16mm cable from the CU Earth bar to the MET, nothing else.
My electrician advised that when the electric company replace the meter, they should upgrade this earthing. So if they bonded the existing 16mm cable to the shroud, wouldn't the CU earth bar BECOME the MET? Problem solved!
And in the meantime, could the CU earth bar be considered to be the MET, and the 'existing MET' considered to be just a means to connect the undersized wire to the 'real MET' in the CU?
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Postby Mr White » Thu Sep 16, 2021 7:47 pm

Earth bonding cables should not be connected inside the consumers unit.
When a consumers unit is properly installed you should easily be able to identify which neutral* and which earth is associated with each MCB as all you need do is count. For example, the 4th MCB, its neutral will be the 4th one along, like wise its earth will be the 4th one along.

Also the regulations say the bonding cables must be connected to the MET
If the DNO supply the wrong size cable, it is not the electricians fault, if there was a fault caused by not doing as per regulations, it IS the electricians fault.



* Assuming it is NOT an RCBO board.
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Postby Tim1 » Thu Sep 16, 2021 11:37 pm

Many thanks Mr White. Understood!
The CU is only around 2 yrs old & has exclusively RCBOs
Does that make a helpful difference?
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Postby Mr White » Fri Sep 17, 2021 6:39 pm

The use of RCBo's in this case makes no differance.
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