BS951 clamp used for TNS?

HappyHippyDad · Nov 28, 2021

I have just completed an EICR.

The earthing is TN-S. However, there is a BS951 clamp used for this. Is this acceptable? Did the DNO ever use this a BS951 as a means for clamping around the supply cable or would this always be DIY?

Ze is 0.23ohms, but that doesn't mean a great deal if the connection is not compliant.

Picture below, albeit a little poor. Ignore the bottom clamp, this is to gas. It is the clamp partially obscured by the meter tails.

[ElectriciansForums.net] BS951 clamp used for TNS?

Lister1987 · Nov 28, 2021

Some did even though they aren't supposed to. Should be either a sweated connection or constant force spring (similar to that used on SWA joints), I'd C2 and a call to 105.

133.1.3 - clamp not appropriate for use.

HappyHippyDad · Nov 28, 2021

Lister1987 said:
Some did even though they aren't supposed to. Should be either a sweated connection or constant force spring (similar to that used on SWA joints), I'd C2 and a call to 105.

133.1.3 - clamp not appropriate for use.

Thanks Lister.

Dustydazzler · Nov 28, 2021

If you do a lot of domestic work you will see loads and loads of pipe bonding clamps used to make a tns connection on the lead sheath

so common in fact that if the clamp looks in good condition and i get a decent Ze , then i don't even bother noting it anymore

Lucien Nunes · Nov 28, 2021

I don't like it at all, personally. Although usually they will give a satisfactory resistance reading, there might only be small points of contact due to the low clamping force, I wouldn't trust it under fault current. If for any reason it penetrates the lead, it can start a fireball that stops only when the substation or feeder pillar fuse blows. Most unlikely, but avoidable, hence I would note it.

R-fur · Nov 28, 2021

They should defintly not be used on lead sheathed cables, the lead will cold flow away from pressure causing the clamp to slacken. As lister says constant tension spring or a wipe. If you report it as high Ze it should be a priority job.

ipf · Nov 28, 2021

Definite 'No, no' for me.
I can't understand why anyone qualified or experienced would do it. It's not matter of the Ze, it could be putting others at risk.
It's bad on swa, too. Steel wire isn't solid.......and neither is the insulation being damaged.

Dave OCD · Nov 28, 2021

That clamp is newish and the same make/age as the main gas bond clamp. So I'm assuming someone felt the need to 'upgrade' during a board change, the original earth was most likely bare etc.
Too many people misguidedly mess with the DNO cable sheath in this way, as Lucien points out there could be a massive fuse behind it - a single service cable can be jointed off a really big cable quite legitimately in line with supply regs so could well be an 800amp fuse or higher ! So in technical terms - bugger that ! ?