Bathroom Earth Bonding - Help?!?

[Pecanfan]

OK, I've read everything there is to know about the subject on t'interweb and I'm significantly more confused than when I first started.

Blank canvas - new bathroom - no earth at present. The ceiling is 2.9m high and the lighting is 12v IP44 rated with an external switch. There's nothing else electric in the bathroom other than the extractor fan, which is double insulated.

I have a metal bath, metal towel radiator (NOT electric), metal shower and (obviously) metal taps. All supply and c/h pipework is copper, all boxed in above floor level, and the mains water supply to the building is plastic. SO...

1. I gather I need to earth my lovely chrome towel radiator with an awful green and yellow cable? How on earth (sorry!) do I do this without having the earth cable dangling up my wall? Would it be sufficient to bond the (microbore) pipework inside the boxing (approx 1ft below the towel radiator itself) or does the actual towel radiator need to have an ugly earth clamp stuck to it?

1b. If my towel radiator MUST be bonded, why doesn't it have a strategic point onto which to attach an earth cable?

1. I read somewhere that if the earth cable is within conduit 4mm^2 is sufficient. Since the earth cable will run (loose) within boxing around the room, does this count as conduit?

1. OK, so I connect everything together with earth clamps and bits of wire - where does this ultimately need to go back to? I've read it's NOT a good idea to take this back to the CU.

2. If I bond everything together within the boxing, to hide unsightly earth cables, will this be sufficient? (the boxing will have removable panels at strategic points) i.e. exactly how close to the taps, towel radiator, shower etc. does the earth wire need to run?

Think that's it! TIA,

Andy

[usenet]

It doesn't need to go anywhere, the object is to ensure that all the bits of metal you can touch are at the same potential as each other.

[andrewpreece]

My Collins DIY book shows each microbore pipe bonded AND the radiator too! My bathroom is not new so there's no way I'm bothering with that: I've only just bonded the flow and return radiator pipes and the gas pipe by the CU, they were only bonded by indirect means before. Rumor has it that compression fittings make good metal to metal contact reliably, so I'm thinking that all this multiple bonding (i.e. 3 lots per adiator ) is a bit OTT. Dunno what the regs say exactly.

To make life difficult for us. It'll most likely be very well bonded via the microbore anyway.

I heard it was 4mm2 if protected, but as small as 2.5mm2 if run in conduit??? Something to do with >=60% of the cross sectional area of the local circuitry ( which is none in my bathroom, unless you count the ceiling light ). I guess that means that 2.5mm2 is more than sufficient if the only danger comes from lighting circuits.

As the other poster said, it is not necessary AFAIK to take it take to the main earth terminal, the fact that all extraneous metal parts in he bathroom are all connected together is sufficient.

Not sure about how close. If you have trouble fitting the clamps, post again: I found out that the ones that I bought needed disassembly then ressembly in a different way to work.

Andy.

[Andy Wade]

OK, so the things to be included in the supplementary bonding are: bath, towel rail, pipework to bath and basin taps and (don't forget) the circuit earth wire (CPC) of the circuit feeding the fan if it's within the zones. This is the lighting circuit, most probably. (If the fan is more than 0.6m horizontally from the edge of the bath and more than 2.3m high then it's outside the zones.)

You can bond to the pipework "in close proximity" to the towel rail - although a normal earth clamp ain't gonna work on microbore tube (AFAIK). If you don't bond to the rail itself then bond to both the flow and return pipes, as a precaution against any high resistance joints in the plumbing.

4mm^2 applies if there's no mechanical protection. Where there is protection you can go down to 2.5mm^2 between extraneous-conductive-parts (pipework, bath, towel rail) and 1mm^2 for the bond to the CPC of the lighting circuit. This doesn't make much difference to the visibility though, so most people just stick to 4mm^2 for everything, thus avoiding the debatable question about whether pipe boxing counts as protection.

Nowhere, necessarily...

... but it will find its way back to the CU earth terminal via the CPC of the lighting circuit, and any other circuits feeding equipment in the bathroom. It's wrong to say "it's NOT a good idea to take this back to the CU" - but it's simply not necessary to do this separately.

Yes, supplementary bonding can usually be done very discreetly, especially if it's not being done as an afterthought. All connections should be accessible, unless crimped or soldered, and labelled "safety electrical connection - do not remove".

HTH

[Lobster]

I've always just bonded the pipework, just below the valve, and have had this passed as OK in Periodic Inspections.

If it was necessary to bond the radiator itself and not just the pipe, then surely by extrapolation that would mean it was necessary to attach clamps directly to all the bath and sink taps as well?!

If not, then what should you use instead? I've never seen any special microbore clamps available?

David

[Pecanfan]

Cheers for the replies - that puts my mind at rest a bit anyway. I meant

2.5mm^2 in the boxing - not 4mm^2 - d'oh!

Building inspector's coming out to this one so will let you know if it all goes horribly awry! :-)

Andy

[Christian McArdle]

Personally, with a blank canvas I would redo the plumbing ensuring at least

1m of plastic between the metalwork (i.e. taps/bath/rad) and the supply. Then not supplementary bond at all. Short lengths of chrome pipe into the boxing/under the floorboards are fine. Unforunately, the inspectors may be too ignorant to realise that such a system is safer than a supplementary bonded metal one.

The IEE guidance suggesting this as a safer course of action now has something like "This is not the advice of the IEE" right under the IEE logo, presumably for legal/insurance reasons. However, its contents are well considered and based on scientific evidence.

Christian.

[zymurgy]

within

Hmm, logically (or even illogically) speaking, would you want to connect the earth bonding to the cpc of a local circuit, wouldn't this potentially increase the risk of a live to earth fault, as you have intentionally moved the protective earth bonding to the close vicinity of the/any live terminals ?

Or am I just being silly ?!

But if it is taken separately you are not intentionally connecting into junction boxes with adjacent lives, it goes back to the star terminal at the cu which only contains earths.

Feel free to shoot me down here, but I have just the same bonding question. I have bonded all exposed metalwork together in the bathroom, including to a cold water pipe. I don't particularly want to link into any local circuits, I was going to take back to the TN-S earth point at the CU.

Let the local circuits find their own earths back via the RCD/CU !

Cheers

Paul.

[Owain]

You run the risk then of (say) a CPC springing out of an earth terminal and (either in the same place or elsewhere, downstream of the fault) shorting to a live. This faulty-live-earth could then be taken into the bathroom and make something live, eg the mounting screws of a flex outlet feeding a double-insulated towel rail. You could then get a full

240V arm-arm shock from the live apparatus in one hand and the cold tap in the other.

The point of equipotential bonding is to ensure that you cannot get a potential difference. If you bond the cold tap to the CPC in the towel rail FCU, you cannot get a shock *between the two*, even if they are both live -- because there is no potential difference.

Anything conductive that comes into the bathroom ie could introduce a potential must be bonded to everything else that might be at a different potential, so there can be no potential difference. Because these things usually include services like CPC and metallic water pipes earthed elsewhere, the euipotential bonding will usually be earthy.

Owain

[Andy Wade]

Methinks you've missed the whole point of supplementary bonding, which is to prevent the appearance of voltage differences - "touch voltages" to use the jargon - as Owain has explained.

Ditto. The whole rationale here is *bonding* rather than *earthing* /per se/. If a bathroom appliance develops an internal earth fault (phase-CPC short) then there will be a significant voltage drop across the length of the CPC until the protective device clears the fault. During this time a potentially lethal touch voltage could exist between the exposed metal parts of the appliance and (say) the water taps & bathtub.

Example: let's say the appliance is an electric shower unit wired in

10mm^2 T&E cable, which has a 4mm^2 CPC. If the supply to the final circuit had negligible impedance then an earth fault in the appliance would cause 10/14 of the mains voltage to appear on the shower unit's case. The unfortunate user is then possibly standing in an earthed metal bath with the shower outlet and pipework at ~160 V. This condition could exist for up to five seconds (the max. allowed fault clearance time for fixed equipment circuits) and the danger of that in a wet-body situation should be obvious.

Then you must be shot down in flames because what you are proposing clearly violates the wiring regulations (BS 7671). Supplementary bonding to exposed-conductive-parts (and therefore the CPCs) of electrical equipment in a bathroom has been required since coming of the

14th edition of the IEE Regs (c. 1966). When the revised Section 601 (bathroom rules) came in to force in 2000 this was modified to require bonding to the CPCs of *all* circuits feeding equipment within the zones, _whether_or_not_ there are exposed-conductive-parts. Thus you must still bond to the relevant CPCs, even if Class 2 equipment is installed. This is clearly intended to provide for safety when equipment is subsequently changed.

HTH

[Miketew]

Then you must be shot down in flames because what you are proposing

clearly violates the wiring regulations (BS 7671). Supplementary bonding to exposed-conductive-parts (and therefore the CPCs) of electrical equipment in a bathroom has been required since coming o the

14th edition of the IEE Regs (c. 1966). When the revised Section 601 (bathroom rules) came in to force in 2000 this was modified to require bonding to the CPCs of *all* circuits feeding equipment within the zones, _whether_or_not_ there are exposed-conductive-parts. Thus you must still bond to the relevant CPCs, even if Class 2 equipment is installed. This is clearly intended to provide for safety when equipment is subsequently changed.

HTH

-- Andy You are of course dead right Andy, the only other thing is that al supplimentary equipotential bonding must be done in 6mmsq cable minimu and there are now special earth bonding clips for radiators, baths etc. finally unless you are a qualified electrician and have registered an been asessed under part P building regs you are breaking the law doin this anyway as bathrooms are clearly defined as risk areas

-- Miketew

[Andy Wade]

Wrong. 4mm^2 covers most requirements in bathrooms, and smaller sizes can be used if mechanical protection is provided. Larger sizes are only required if you're bonding two CPCs of >=6mm^2, or one CPC of >=10mm^2 to extraneous-conductive-parts. Table 10B in the OSG provides a useful summary.

Wrong again, although a building notice is required for work in a 'special location' (which does include a bathroom, within the Zones).

[Miketew]

Then you must be shot down in flames because what you are proposing

clearly violates the wiring regulations (BS 7671). Supplementary bonding to exposed-conductive-parts (and therefore the CPCs) of electrical equipment in a bathroom has been required since coming o the

14th edition of the IEE Regs (c. 1966). When the revised Section 601 (bathroom rules) came in to force in 2000 this was modified to require bonding to the CPCs of *all* circuits feeding equipment within the zones, _whether_or_not_ there are exposed-conductive-parts. Thus you must still bond to the relevant CPCs, even if Class 2 equipment is installed. This is clearly intended to provide for safety when equipment is subsequently changed.

HTH

-- Andy

The min supplementary bonding cable is 6mm sqd now

-- Miketew

[Lobster]

If so, where is this published?

David

[Andy Wade]

It isn't, he's wrong. Regulations 547-03-xx and Table 10B in the OSG stipulate 4mm^2, except as noted in my previous article. There has been no change since the publication of the original 16th Edition in 1992.

[Miketew]

Your right Andy I had glanced at 547-02-01 main equipotential no supplementary

-- Miketew