supplementary bonding in bathroom

[deckertim]

I'm renovating my bathroom at the moment and currently there is no supplementary bonding. I have read several threads on uk diy, but I remain uncertain about some points.

As I understand it

All exposed metal work should be bonded together. This doesn't extend to things like loo roll holders etc. that are isolated.

Provided the bonding is protected it can be done using 2.5mm cable. In my case all bonding is going to be carried out within the void under the bath or within a false wall I am having to build. This will be accessible, but only by unscrewing an access hatch or bath panel.

I have a light fitted which has a metal case. This is mounted on the wall, but is fed from a junction box in the false wall. As the junction box is at the foot of the wall near to where the taps and radiators are bonded, can I simply connect these to the cpc at the junction box and avoid having a separate cable from the light down to the radiator.

There is no need to actually link this bonding back to a cpc on the lighting or shower circuit. But because I have a shower and a light in the room these will be linked to the bonding anyway.

Please confirm that I have got this right.

Thanks, Tim

[Christian McArdle]

Use 4mm. Providing protection is normally not practicable.

An adjacent junction box is an acceptable location for running the supplementary bonding.

Personally, I would regard the junction box as too far from the light, so unacceptable unless the CPC was 4mm, which is VERY unlikely. However, it would be acceptable if the CPC was protected, such as being in a metallic conduit, and otherwise met supplementary bonding regulations for minimum size.

There is if you have lighting or a shower.

Christian.

[Andy Wade]

Provided that the run from the JB to the light is fairly direct and is in T&E cable I don't see why bonding to the CPC in the JB wouldn't be OK. A CPC in a sheathed cable is deemed to be protected for this purpose [see Regs. 547-03-01 to -03].

Bonding to the lighting circuit's CPC is not required if the light and any other accessories on the circuit (e.g. shaver point, fan) are outside the Zones.

[Christian McArdle]

Ah. I had missed that one. I had thought that protected had the same meaning as for buried cable runs. That's useful to know.

Christian.

[Ed Sirett]

...or are Class II equipment?

[RzB]

===Clip

Hmm - OK I'm Confused... and on re reading the regs I'm still confused.. I expected one of the Gurus to chip in that 4mm was needed not 2.5mm.

I had thought that 4mm cable in a nice green/yellow cover running round the bathroom was the way to go..

In sections 547-03-02 & 03 what is the meaning of "sheath" and "mechanical protection".. These don't get spelled out in the definitions.

Is "Sheath" the green/yellow plastic stuff? What is "mechanical protection" in this context? The side of a bath? Steel conduit? And why should the type of protection dramatically affect the diameter of the bonding...

Hmm - I'm obviously confused - could somone please spell out

547-03-02 & 03 in simple terms!

Many thanks, Roy

[Andy Wade]

No, the CPCs of circuits feeding equipment within the Zones should be bonded, even if all such equipment is Class 2. That was one of the significant changes made when the new bathroom rules were introduced in

2000. I've always assumed it's so that the bonding is already in place for when replacement Class 1 fittings get installed.

[Andy Wade]

It is, usually. You "can't go wrong" if you use 4.

No, that's insulation. All separate protective conductors of 6 mm^2 or less have to be insulated [543-03-02].

Sheath is a second layer of PVC, usually grey, like the outer of twin-and-earth cable or meter tails.

I've always assumed it to mean "enclosed in some recognised form of wiring system" - i.e. conduit (steel or PVC) or trunking (including mini-trunking). The intent of the regs is to prevent separate thin easily-broken wires being used. IOW 4 mm^2 is considered sufficiently robust not to get damaged, even if not enclosed.

547-03-02: For electrical purposes the size of bonding between electrical circuit earths (CPCs of e.g. shower and lighting circuits) and extraneous-conductive-parts (e.g. heating pipes) must be at least half the size of the relevant CPC, but subject to a minimum of 4 mm^2 for reasons of mechanical robustness if not enclosed. 547-03-03: Same thing, but between two extraneous-conductive-parts. Electrical: 2.5 min, but 4 if not enclosed.

There is another constraint in 413-02-28 which imposes resistance limits for supplementary bonding. In principle this could mandate larger sizes than 547-03-xx, - but not in a normal-size bathroom.

HTH

[RzB]

Andy,

Ahh - all a little clearer now.

I'll stick to 4mm and all will be well... :-)

Thanks for your excellent response,

Roy