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Adding a bonding conductor to an existing main earth terminal

Electron666

Hi do you need to isolate the supply to a commercial building to connect a 16mm2 bonding conductor to the MET in relation to BS 7671 or HSE?

It isn't something I can find explicit guidance on.

The MET is at the intake and separate to the main LV board.

It is easily accessible without coming into contact with L&N conductors connected to the main LV board.

The earthing system is either TN-S or TN-C-S.

Isolating the supply is possible if required but would be costly, require multiple companies attending out of hours and would need to be planned in well in advance due to it being a refrigerated / food storage facility.

I note all these reasons are inconvenience related which is secondary to health and safety. Therefore, I'm only asking if there is a method that is commonly used such as standing on rubber mats or wearing rated gloves etc that is considered safe and proportionate to the to the small task being carried out.

Thanks

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    If  adding the additional bit of green and yellow requires you to remove other connections that are already there - which might interrupt a fault current, and allow voltage to appear on things that are supposed to be earthed, then there is a serious risk. However if it is a wire into an spare terminal tunnel just adding one more bit of wire to a collection of stuff that is already earthed and exposed, like radiators and other plumbing, is not a significant extra risk.

     Note that turning the supply off won't greatly reduce the risks from  touching the earth terminal or  exposed metal already attached to it, and  if you have concerns, it is more useful to test for voltage with an insulated wander lead between the things you are proposing to connect and the MET, before you actually do.

    regards Mike.

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  • 0

    If  adding the additional bit of green and yellow requires you to remove other connections that are already there - which might interrupt a fault current, and allow voltage to appear on things that are supposed to be earthed, then there is a serious risk. However if it is a wire into an spare terminal tunnel just adding one more bit of wire to a collection of stuff that is already earthed and exposed, like radiators and other plumbing, is not a significant extra risk.

     Note that turning the supply off won't greatly reduce the risks from  touching the earth terminal or  exposed metal already attached to it, and  if you have concerns, it is more useful to test for voltage with an insulated wander lead between the things you are proposing to connect and the MET, before you actually do.

    regards Mike.

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  • 0 in reply to mapj1
    mapj1 said:
    adding the additional bit of green and yellow requires you to remove other connections that are already there - which might interrupt a fault current,

    or intended protected conductor current ... or indeed 'diverted neutral current'.

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