Earth continuity with TN-S supply

[ban-all-sheds]

Just had a guy from my supplier round to investigate re quoting me for a meter move. Which looks like being unreasonably expensive because the supply cable loops through my service head to supply my next door neighbour:

A question which occurred to me after he'd left is is there a link inside the head between the sheaths on the two cables?

Or does my neighbour's earth rely on me not disconnecting (or accidentally breaking) the two main earth cables which go to my MET?:

You can't see it in the photo, but one of those 2 conductors is sweated onto one cable, the other onto the other one. And so are even more undersized than I'd previously thought (hadn't realised until I poked about just now that they went to separate sheaths).

 

[Steve]

Hi ban, hope you're doing ok! I would like to think there's a link in the cutout, but you know what the DNO are like

 

[JohnD]

is the old entry box cast iron?

 

[gcresser]

I know it is an old post, but It interested me. To me it looks like the bare tinned wires going to you MET are from the DNO cables, ie one from each. As the chamber of the cut-out is bitumin filled, I'd doubt very much there is a link in there hence the sweating external, below.

So yes, I'd say you are correct that it you cut them, your neighbour's earth will be no more!

 

[ban-all-sheds]

I know it is an old post,

Posted: Tue Aug 21, 2007 12:40 pm

So yes, I'd say you are correct that it you cut them, your neighbour's earth will be no more!

Well - I wouldn't cut them both, only his...

Not really....

In his shoes I'd be pretty pissed of by this, because he's presumably blissfully unaware right now- I expect that under his stairs he sees a cutout, with one cable, one sweated earth (albeit a desperately undersized one - 7/.026 I reckon), and no reason not to think it doesn't come straight from the street.

Even a sparks looking at it wouldn't know, if he'd never been in any of the 50% of the houses in the street where it's like mine. And of course it would test out OK, as long as the flylead was intact.

I could ask my neighbour if I can check his Ze, but he's a builder, so he may have a tame sparks that he can get to go in and have a look - get him to remove his main bonding, measure Ze, then I'll disconnect the flyleads from my MET and he can test again.

 

[ban-all-sheds]

is the old entry box cast iron?

No - good old 1950's Bakelite.

 

[gcresser]

Sorry, looked at the wrong date! new to this forum [/quote]

 

[Adam_151]

(albeit a desperately undersized one - 7/.026 I reckon), and no reason not to think it doesn't come straight from the street.

Whats your Ze? I reckon its not quite as desperate as it appears on the surface, even by BS7671 standards, and considering the DNOs way of working seems to cut a little closer to the bone than BS7671 ever did, it might even be considered adequate by them!

It should handle a fault on any of your final circuits just fine, and if it ever needs to carry current that causes the main fuse to operate, it may get a tad warm, but then again its not covered with PVC and its a once in a blue moon event.

I'd perhaps be a little careful of poking a lead and paper cable too much! (though I suppose as long as you don't try and do anything daft, like try and change the bends, eg pull it away or push it into the wall, it should be ok)

 

[ban-all-sheds]

Whats your Ze?

Dunno - keep meaning to measure it, but never get round to it.

I reckon its not quite as desperate as it appears on the surface, even by BS7671 standards, and considering the DNOs way of working seems to cut a little closer to the bone than BS7671 ever did, it might even be considered adequate by them!

Makes a mockery of 10mm² and 16mm² earthing and bonding cables though..

I'd perhaps be a little careful of poking a lead and paper cable too much! (though I suppose as long as you don't try and do anything daft, like try and change the bends, eg pull it away or push it into the wall, it should be ok)

Don't plan on doing anything like that...

 

[ban-all-sheds]

Thinking some more, I will measure my Ze asap - his is probably the same.

Dunno what service fuse I have (yet ) but I'll assume 80A.

I want to work out the let-through on an earth fault, and see how that 2.5mm-ish flylead will hold up. If there's a possibility, even a blue-moon one, that a fault in my neighbours house could start a fire in mine I shall be a very unhappy customer indeed...