Metal - clad buildings and the confused forum member.

Sparkingchip:

..

UK plumbers, gas fitters and others rarely bother to use temporary bonding kits when cutting sections of metal pipework out, you often see the kits hanging up in their vans, but that’s where they stay..

I have 2 sets of beefy jump leads in the van. Never saw the need for those puny temp bonding kits either. Gas fitters should be using them, part of the training and reassessment, doubt plumbers are aware of it though.

OlympusMons:

Sparkingchip:

..

UK plumbers, gas fitters and others rarely bother to use temporary bonding kits when cutting sections of metal pipework out, you often see the kits hanging up in their vans, but that’s where they stay..

I have 2 sets of beefy jump leads in the van. Never saw the need for those puny temp bonding kits either. Gas fitters should be using them, part of the training and reassessment, doubt plumbers are aware of it though.

I had to help two plumbers jump start their van which was parked the wrong way around, this was achieved by using two sets of jump leads and two three metre lengths of copper pipe to link them.


Andy B.

AJJewsbury:

The importance of this relates to Regulation 442.2.1 (in this case, if you are one of the TT consumers, you are having to rely on an additional earth electrode in someone else's installation - so how can the designer ensure BS 7671 is complied with)

As I see it, if it was a pure TT system there wouldn't be an issue (U_f would be zero). The problem comes from the influence of the PME earthing system supplying another unit - but that PME earth itself presumably satisfies the requirements of 442.2.1 (presumably by some approximation to a 'global earthing system') - so I'm thinking that if the PME earth in the other unit is deemed safe, then it's influence in our TT unit can't be any more dangerous.


 

If the building is metal-clad, but doesn't have any metal framework in good contact with the ground (e.g. metal frame on brick or block walls), then there could be an issue.


If there are no other metallic services running down the side of the premises, the influence of the global earthing system is uncertain - if the next unit is a suitable distance away, it is "TT" proper, and yes no problem. The difficulty comes "in between" - and I guess the DNO will (or should) assess that in determining the approach.


The difficulty is, it's the installation designer (who might be the installer) who has to comply with BS 7671, but it's not always easy to determine whether you've done so or not in some cases ...