Earth bonding cable - minimum size?

[Lobster]

Hi

Just completing a house wiring job, I've now got myself a tad confused about what size of earth cable I should be using to bond the incoming gas and water pipes to the main earth near the electric meter. I've already used 10mm, but have got myself worried that this isn't big enough and would rather get it right now than have the inspector tell me to change it later (it's not a trivial task, as the gas and electric meters are at opposite ends of the house!)

The electricity installation is new (and not yet connected to the CU), and it's PME. The earth cable is completely protected mechanically along its length... is there any other info needed to assess the correct earth size? Or do I need to ask the supply company, ahich is what the stuff at

seems to be suggesting?

Many thanks David

[BigWallop]

From the mains service head you need to run 10 mm csa' green/yellow sheathed conductors. On all the other supplementary bonding you would use 6 mm csa' green/yellow sheathed conductors.

[Lurch]

On 25 May 2004 11:09:27 -0700, [e-mail] (Lobster) strung together this:

10mm cables for the equipotential, i.e. gas, water and any other services and structural metalwork, and 4mm for the supplementary if required, i.e. cross bonding in the bathroom.

I'd be very surprised if it was.

Nope, that's it.

[Andy Wade]

That's not quite true because of the note above Table 54H in the regs which says "Local public electricity supply network conditions may require a larger conductor" - so, strictly speaking, you should check with the relevant distributor to see if they require a larger size.

I've no idea how often this applies, but when I used to have dealings with the old Eastern Electricity on such matters they certainly preferred the use of 16mm^2 main bonding. The issue may also come up in London, where fault levels tend to be higher.

Given that you need a reel of 16 mm^2 cable for the main earthing conductor, you may as well use the same size for main bonding, just to be on the safe side, and avoid having to carry a reel of 10mm^2 as well.

[Lurch]

On Wed, 26 May 2004 00:02:53 +0100, "Andy Wade" strung together this:

Fair point, however it is 'most likely'' that 10mm will suffice. I doubt anyone at wherever it is that the OP rings will have a clue what he's on about anyway!

Can't say as I've ever come across any of that, just goes to show.

Hmmm, you can, I'll stick to 10mm thanks! I can't see someone rewiring there own house buying 100m of 16mm earth to use 3m of it though! I think you're aiming your comments at the profesionals now, shouldn't that be moved OT!

[Z]

In article , BigWallop writes

Though if you have a drum of 10 use 10 save ending up with 2 half drums

[Z]

In article , Lurch writes

Even then many companies as per NIECIC use 10 throughout.

[Lobster]

together this:

Thanks everyone, that's a relief!

Maybe you're right there... "completely protected mechanically" is a rather vague phrase I keep seeing in the relevant documentation on this topic, as being one of the criteria for deciding the size of cable to use. I took it to mean that the earth cable was hidden from sight/possible damage - mine is inside stud partitions or under floorboards along its whole length, rather than being attached to skirting boards(!) or whatever.

David

[Lurch]

On 25 May 2004 23:49:16 -0700, [e-mail] (Lobster) strung together this:

I thought that would be the case, it's not mechanically protected then. Mechanically protected would mean it was enclosed in conduit or trunking throught its entire length, including its passage through walls and the like. That's something else you've learnt today! ;-)

[usenet]

Doesn't "mechanically protected" in the context of earth bonding mean simply that it's not bare wire? On the other hand maybe that's just "pretected against corrosion", on looking at my OSG it's not at all clear what is meant by either of these terms.

Can anyone give a definitive meaning of "mechanically protected" and "protected against corrosion" when applied to earth bonding wires?

[BigWallop]

"Mechanically Protected" is sheathed within a covering that does not yield easily to applied pressure or striking.

"Protected from corrosion" is where the system is not allowed to come into contact with dampness or chemical ingress that may cause the conductors or its insulation to breakdown and weaken it properties of doing its job properly.

[Andy Wade]

Yes, that occurred to me - getting through to someone that can answer technical questions ain't easy.

A 50m reel isn't particularly expensive though, and you'll probably need more than 3m to get to the water and gas pipes...

[BigWallop]

Yeah, why not. Very good point.