TN-S Earth clamp

[ben]

Had a proper look at the earthing on the new place today. The supply earth is provided by a clamp onto the sheath. It's not, so far as I can, a tightenable clamp.

It has a 10mm cable in which looks like it only just fits, can't see how I'd get a 16 in there. (tails are - at the moment - 25mm as far as a Henley, then down to 16mm)

I noticed that the clamp rotates freely around the sheath. Is that to be expected? I will get round to measuring the earth soon when the replacement test lead turns up.

[Andy Burns]

Crimp a ring terminal on the cable? Depends what size ratchet crimp you've got/can borrow?

[ben]

Thanks!. Why didn't I think of that.

My crimper stops at 10mm, but I'm sure I can find someone with a 16.

[Robin]

FWLIW I think I'd ask if a "proper" PME can be supplied

[ben]

I was considering that. Assuming the clamp isn't expected to move as it does (??) I was going to call up and express concern about it, and see if that ended up with a PME conversion.

[Robin]

I was leaving the clamp to my youngers and betters :) But FWIW (a) a clamp that moves patently means your Ze can change randomly, (b) clamps (even constant force clamps) on lead sheathing are now a no-no, and (c) I think tightening a clamp is for the brave and courageous.

*-- Robin reply-to address is (intended to be) valid

[Jack Harry Teesdale]

No, the clamp should not move and will be an ineffective earth connection.

Report it to your DNO and they should either rectify it or provide PME. (this may be delayed due to Coronovirus Regs)

[bblaukopf]

Thanks. That's what I thought, but nice to have it confirmed.

I rang up UK power and they were somewhat unhelpful, and want to know what Ze is before they will do anything (I tried arguing that what it is NOW is irrelevant, and I don't want to start waggling their clamp to demonstrate that it will change). Well, gives me something to do. I will call back and hope I get someone more helpful.

There's a lead water main. Turns out it does have its uses....

[Scott]

You would always give them an 'estimated' figure :-)

[tabbypurr]

If you're 100% RCDed it's not ideal, but not an immediate threat to life. If you're not RCDed it is.

Be aware that they will only reconnect your supply after the work if your water & gas/oil are bonded.

NT

[Robin]

and IIRC to current (continuous 10mm) standard

[bblaukopf]

Sorting out the bonding mess was how I noticed the problem in the first place!

[ARW]

More likely they will not commence work if they are not bonded.

[ARW]

Assuming that the electric co are not complete dickheads then they will probably install an isolator and earth block but not actually connect back up your power or the earth.

It's a 15 minute DIY job that does not require an electrician just a flat screwdriver, allen keys and snips (or Stanley knife if you prefer) to connect into these [1]

If you do need to cut any meter seals I have loads of NE ones available.

I doubt they will PME it. I suspect they will jut fit a series 6 cutout and keep it as a TN-S.

[1] Not allowing for the 30 minutes to find the Allen keys that you put somewhere safe the last time you used them:-)

[ARW]

Especially after slackening the earth clamp off.

Couple of ohms should do it.

I like your thinking.

[Roger Hayter]

What does 'continuous' mean in this context? Surely it doesn't mean no joints? Or does it means no thinner sections?

[bblaukopf]

It means if your water bond is on the way to the gas, so you do it all in one length, make sure it is one length(not cut). That way if someone disconnects the water bond, gas is still bonded.

I think I learned that here, but I've seen it referenced elsewhere too.

[Roger Hayter]

But a terminal block fixed to the wall with separate wires to gas and water would be ok? Depends on the precise layout which is ieasier.

[Robin]

Yes - sorry I was misleadingly vague.

AIUI it's not mandatory part of BS7671 but something that BS7430 and Guidance Note 8 says "should" be done - and makes for a quieter life.

And while there's no regulation against joints in main bonding with junction boxes (or chock strip) suitably labelled I'd extend with an uninsulated crimp.

PS

Sorry too that for some reason I thought I knew UKPN was your DNO.

[ARW]

Call it an earth marshalled busbar terminal and all is fine.