Equipotential bonding

[baz]

Their seems to be some confusion on the site concerning bonding in domestic premisis, here it is in a nutshell. Main bonding with green/yellow 10mm square (See table 54H of BS 7671 The IEE Regulations) from main earth terminal either in the board or from the supplied main earth terminal link. Connect to incoming gas supply on hard pipes (not lead) within 600mm of the meter and before any tee. Connect to incoming water supply on hard pipes (not lead) on the consumers side of the stop valve and across the meter if one is fitted. A similar connection must be made to any other incoming services such as oil pipes. The connection to the pipes must be made using a bonding clamp complying to BS 951 with a label attached SAFETY ELECTRICAL CONNECTION DO NOT REMOVE. You may loop from one service to another with the bonding lead, but if you do this you must not cut the lead, just strip off the insulation and wrap it around the screw on the clamp. Clean the pipes and ensure tight connections. Get it tested by a qualified electrician.

Supplimentary bonding with 4.0 mm square green/yellow to hard pipes using BS 951 clamps and labels, connect to earth at the nearest socket outlet, immersion heater switch, shower switch or fused connection unit. DO NOT RUN IT BACK TO THE CONSUMER UNIT. If you need more advive get a copy of the On Site Guide (ISBN 0 8526

987 2) around =A317 and read it ALL, don't ignore the bits you don't understand. they know better than you do.

[Andy Wade]

Whose?

What site?

That is not a requirement of BS 7671, although it is considered good practice.

[sic]

Pardon? There's no need to earth your supplementary bonding in this way. You merely connect together all exposed- and extraneous-conductive-parts (as defined in BS 7671) in the bathroom zones. The bonding will be earthed via the CPCs connected to any exposed conductive parts, but if only extraneous-conductive-parts are involved the bonding will not necessarily have a metallic conductive path back to the main earth terminal.

You could have added that it is necessary to bond the CPCs of all circuits connected to wiring 'points' within the zones, _even_if_ Class

2 equipment is installed. This will typically apply to shaver points and luminaires. The CPCs between such points, provided they take short and fairly direct routes, can be used as the bonding, so you don't need to take separate 4mm^2 wires to each point (one connection will do).

That's the ISBN for an obsolete version. The ISBN of the current version is 0863413749. The newer "Electrician's Guide to the Building Regulations" (ISBN 086341463X) is also to be recommended.

[John Rumm]

or Figs 4a/b/c in OSG

Might be worth adding that this is true for TN-S and TN-C-S supplies, but with TT you only actually require 6mm^2

Given that this is a DIY newsgroup, that last bit does kind of defeat the purpose of DIYing the first bit (not suggesting testing it is wrong, only that posting a suitable test procedure would be more useful) ;-)

Yup good book... currently £15 at Amazon:

[ARWadsworth]

The OSG says that the cable must be looped with unbroken connections on main equipotential bonding.

Adam

[Andy Wade]

Oh yes, so it does - in one of the footnotes to Fig 4b. Thanks for making that point.

[Phil Addison]

Its just a common error/typo for "there" - we've all done it.

I think baz is referring to the "Earthing and Equi-potential Bonding" section of the FAQ at

that section in fact wrong/outdated? If so would anyone care to write an up to date replacement text for it?

While we're at it, the "Electricity System Earthing Arrangements" section could do with (IMO) some explanatory text to give the pros and cons of the various systems. As it stands it is basically a definition of the various cryptic terms; TN-C, TN-S etc, but a DIY-er is likely to want to (a) check if his system is appropriate, or (b) decide which type to use in a new/revised installation. Some diagrams would be useful too.

Phil The uk.d-i-y FAQ is at

Google uk.d-i-y archive is at NOSPAM from address to email me

[Phil Addison]

What's a "hard (not lead)" pipe? Are you talking about metal pipes or what? Don't forget this is a DIY group so it helps to explain non-obvious terms.

Phil The uk.d-i-y FAQ is at

Google uk.d-i-y archive is at NOSPAM from address to email me

[John Rumm]

The bit on conductor size could do with an update - currently it (by default) gives the wrong information for TN-S systems.

Since the topic of feeding supplies to outbuildings crops up ferequently, the PME section could do with an update. It comments on the reason why rigour in application of eq bonding is particularly important with this system. It could perhaps include additional notes to point out that when the supply is extended into outbuildings the equipotential zone needs to be maintained and extended along with it (or the outbuilding converted to TT).

Andy's section on the wiring regs could do with mentioning the current (brown cover) versions.

[John Rumm]

I presume hard equates to conductive metal (copper, steel etc), but not lead...

However it does beg the question what to do in houses still plumbed exclusively in lead...

[chris French]

Is lead not conductive (I can imagine the surface corrosion might not be)

For most of my old house's life the lead water main was the main earth

[Dave Stanton]

Just to be pedantic, this is Usenet newsgroup, not a site.

Dave

[Andrew Gabriel]

Yes, that's horribly out of date.

[meow2222]

Its too soft to get enough pressure on it to maintain a long term reliable connection.

NT

[Andy Wade]

If there's a worry it's that lead creeps under load, so an earth clamp may become loose over time. However I don't think there's anything in the OSG saying thou shall't not clamp to lead pipes.

And in millions of houses the main earth connection is made to the lead sheath of the service cable (TN-S).

[Phil Addison]

Is anyone up for giving me some updates, or should it taken out of the FAQ altogether?

Phil The uk.d-i-y FAQ is at

Google uk.d-i-y archive is at NOSPAM from address to email me

[Phil Addison]

Good point - in fact you could say "will become loose over time".

Seems like a bad idea.

But that is supported by 'hard' material underneath so would not squash and loosen (er... hardly at all).

Phil The uk.d-i-y FAQ is at

Google uk.d-i-y archive is at NOSPAM from address to email me

[chris French]

In message , Phil Addison writes

not convinced by this, at least in the sorts of time scales that matter here, when I rewired the house and got a 'proper ' earth. the cables clamped the earth to the lead pipe were still secure,

>

[John]

Not really much difference to having pressurised water inside the tube. Also I reckon the thickness of the walls of mains carrying lead water pipe round here (11lb mostly) doesn't give much opportunity for easy deformation. I can't ever recall actually finding an earth clamp which could be described as loose, either a "modern" type or one of the old type which were expanded after wrapping multiple turns of wire round the pipe and clip.

[chris French]

Like I said in my other post the ones in my old house had remained tight for many decades.