Earthing roof beams and roofing sheets on an attached garage.

[spantheman]

My friend has a conundrum regarding earthing the metal parts of his garage. It's an extension to his home which is on a TT supply, It's of concrete block construction with a metal roof, attached to timbers but touching 3 RSJ's which supports the whole roof. None of which is bonded. There are tw/e cables crossing over the beams, so I suggested 10mm equipotential bonding from the beans to the MET. Question is, what needs to be done with the roofing sheets, as bonding could be problematic and cause the roof to corrode? Any ideas would be most welcome.

 

[KungFuTurkeyLeg]

Bit of a chore but you could just put the cable in plastic conduit. Or use split conduit to save disconnecting wires.

 

[Mike Johnson]

How do I determine an extraneous conductive part?

This article provides some simple guidance on how to identify extraneous conductive parts to help you avoid the unnecessary installation of protective bonding conductors. It should be appreciated that exposed metallic parts not forming part of the electrical installation are not always...

electricalapprentice.co.uk

 

[DPG]

My friend has a conundrum regarding earthing the metal parts of his garage. It's an extension to his home which is on a TT supply, It's of concrete block construction with a metal roof, attached to timbers but touching 3 RSJ's which supports the whole roof. None of which is bonded. There are tw/e cables crossing over the beams, so I suggested 10mm equipotential bonding from the beans to the MET. Question is, what needs to be done with the roofing sheets, as bonding could be problematic and cause the roof to corrode? Any ideas would be most welcome.

But what potential are these beams introducing?

 

[Lou]

Welcome to the forum, thanks for joining and asking your question! Have you got any photos of the job? It may help our members to give the appropriate advice!

Thanks

 

[spantheman]

Bit of a chore but you could just put the cable in plastic conduit. Or use split conduit to save disconnecting wires.

Thanks,I did wonder whether that was an option, certainly less faff!

 

[spantheman]

How do I determine an extraneous conductive part?

This article provides some simple guidance on how to identify extraneous conductive parts to help you avoid the unnecessary installation of protective bonding conductors. It should be appreciated that exposed metallic parts not forming part of the electrical installation are not always...

electricalapprentice.co.uk

Thanks, I did the resistance check to the beams and it was 24K ohms, so in theory isn't extraneous, but I didn't check the roof sheets as they were touching the beams anyway. I'm assuming the equipotential bonding still applies to the the beams regardless as they are structural steels and within touching distance, however, it would appear to introduce an unnecessary risk, so perhaps bonding isn't the answer. It's a shame there's not more clarity in the regs for differing construction methods, and it leaves installers in a damned if you do or damned if you dont scenario.

 

[DPG]

Thanks, I did the resistance check to the beams and it was 24K ohms, so in theory isn't extraneous, but I didn't check the roof sheets as they were touching the beams anyway. I'm assuming the equipotential bonding still applies to the the beams regardless as they are structural steels and within touching distance, however, it would appear to introduce an unnecessary risk, so perhaps bonding isn't the answer. It's a shame there's not more clarity in the regs for differing construction methods, and it leaves installers in a damned if you do or damned if you dont scenario.

But if they aren't extraneous then why connect them to to the electrical system?

 

[mainline]

It's a shame there's not more clarity in the regs for differing construction methods, and it leaves installers in a damned if you do or damned if you dont scenario.

it is quite clear in the regs if it’s not extraneous then it doesn’t need bonding.

 

[Dan]

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[bigspark17]

Thanks, I did the resistance check to the beams and it was 24K ohms, so in theory isn't extraneous, but I didn't check the roof sheets as they were touching the beams anyway. I'm assuming the equipotential bonding still applies to the the beams regardless as they are structural steels and within touching distance, however, it would appear to introduce an unnecessary risk, so perhaps bonding isn't the answer. It's a shame there's not more clarity in the regs for differing construction methods, and it leaves installers in a damned if you do or damned if you dont scenario.

Not really its clear in black and white. Not knowing the regs isnt the regs books fault.