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Topic Title: Bathroom supplementary bonding
Topic Summary: Metallic baths
Created On: 17 January 2013 10:42 AM
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 17 January 2013 10:42 AM
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andrew331

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Hi,

I have just noticed that 701.415.2 does not mention metallic baths.

701.415.2 (i), (ii), and (iii) are the same as 601-04-01 in the 16th edition, but no mention of ' metallic baths and metallic shower basins' ((iv) in the 16th).

Does anyone know the reason why this was dropped?
 17 January 2013 10:54 AM
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AJJewsbury

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I'd guess because that metal baths etc aren't of themselves extraneous-conductive-parts (i.e. they can't introduce a potential into the location), so no more require bonding than a metal bath-plug chain. If they could be at a different potential as a result of being connected to metal pipework, then it's the pipework that's extraneous and should be bonded.
- Andy.
 17 January 2013 11:44 AM
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daveparry1

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i.e. they can't introduce a potential into the location
-------------------
It could if it has an old lead or copper waste pipe Andy!

Dave.
 17 January 2013 01:18 PM
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AJJewsbury

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It could if it has an old lead or copper waste pipe Andy!

No, it's still the pipework, not the bath, that introduces the potential into the bathroom. Bond the pipework and the problem with the bath goes away.
- Andy.
 17 January 2013 02:56 PM
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OMS

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I guess the only exception to that would be a metallic bath sat on an un-insulated slab with no DPC - the slab itself may be "earthy" so bonding the bath would be the only alternative ?

Regards

OMS

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Failure is always an option
 17 January 2013 03:07 PM
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daveparry1

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OK Andy, so how about a metal bath with a lead or copper waste pipe going into a cast iron soil pipe which in turn goes into the ground, that could surely cause an earth potential which is often mentioned?

Dave.
 17 January 2013 03:27 PM
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geov

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That's covered in the Regs. The waste is an extraneous conductive part and would be bonded in the situation you describe.
 17 January 2013 05:07 PM
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AJJewsbury

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OK Andy, so how about a metal bath with a lead or copper waste pipe going into a cast iron soil pipe which in turn goes into the ground, that could surely cause an earth potential which is often mentioned?

Absolutely correct, but the general principle is to bond as close as practical to the point of entry into the area to be protected - so in the case of a bathroom, where the metalwork enters the bathroom - which unless you have a very strange layout with the bath half-in and half-out of the bathroom, the point to bond it would be on the pipework rather than the bath.

(If the metalwork is bringing in a potential from outside the installation, it'll want main bonding too!)

- Andy.
 17 January 2013 05:36 PM
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spinlondon

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Dave, it's the pipework that's extraneous and requires bonding, not the bath.
 17 January 2013 06:59 PM
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daveparry1

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True Spin but to my mind if both the pipe and bath are metal and they're connected together they would both end up at the same potential!
 17 January 2013 08:29 PM
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andrew331

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Thanks for the replies.

I see old installations where pipework is bonded to other pipework only but there is no connection to cpcs of say shower or lighting circuits. Was there a time when this would have complied with the regulations?
Also could anyone tell me when requirements for supplementary bonding where introduced?
 17 January 2013 11:07 PM
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AJJewsbury

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True Spin but to my mind if both the pipe and bath are metal and they're connected together they would both end up at the same potential!

Indeed, and as long as they're solidly connected together you could attach the bond to any point with similar results - there's no need to bond every item individually as they're all connected together already. But if you want the system to be robust to plumbers replacing a trap with a plastic one or the like, you'll need to attach the bond closest to the point where the potential enters the location - i.e. on the pipework. If an insulator is then introduced, the bath looses its connection to the bonding, but simultaneously looses connection to the introduced potential - so negating the need to bond it. So put the bond in the right place and it all comes out in the wash.

- Andy.
 17 January 2013 11:14 PM
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AJJewsbury

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I see old installations where pipework is bonded to other pipework only but there is no connection to cpcs of say shower or lighting circuits. Was there a time when this would have complied with the regulations?
Also could anyone tell me when requirements for supplementary bonding where introduced?

It's been done in a variety of ways for a long time. Off the top of my head:

15th Ed - something akin to main bonding was spread around the plumbing system - you'd often see 6mm2+ bonds between pipes under taps in kitchens and bathrooms.

Early 16th Ed - supplementary bonding appears (typically in 4mm2), but initially was just between extraneous-conductive-parts and exposed-conductive-parts (rather than to c.p.c.s) - so if all-insulated fittings were used, supp bonding might still be just between the pipes.

I think it was a later 16th amendment (probably the one that brought in zones for bathrooms) that switched to bonding c.p.c. rather than exposed-conductive-parts.

Those with better memories/libraries will probably be able to refine my recollections substantially!

- Andy.
 21 January 2013 09:20 PM
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andrew331

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Thanks Andy. Early 16th sounds about right to me.

Another one for you;

701.415.2 requires '....connecting together the terminals of the protective conductor of each circuit supplying Class I and Class II equipment to the accessible extraneous-conductive parts....'

Is it right to say that a circuit supplying 12v lights via SELV transformers (ClassIII) would not require connecting?
 21 January 2013 09:41 PM
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AJJewsbury

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701.415.2 requires '....connecting together the terminals of the protective conductor of each circuit supplying Class I and Class II equipment to the accessible extraneous-conductive parts....'

Is it right to say that a circuit supplying 12v lights via SELV transformers (ClassIII) would not require connecting?

The lights will be class III, but the transformer is likely to be class II or class I. The exposed-conductive-parts of the lights shouldn't be bonded (in fact mustn't be connected to earth in any way - see 414.4.4). So it depends where the transformer is located -if it's within the location (i.e. the room, even if it's outside zones) it's 230V primary circuit will fall into the requirement and so its c.p.c. should be connected to the supplementary bonding system.

- Andy.
 22 January 2013 06:55 PM
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andrew331

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Thanks
What I am thinking is if the switch is outside the room, the wiring is above the ceiling, the transformers (SELV) are above the ceiling and only the lights are in the location, then no connection to the cpc would be needed. Now, if the switch is inside the location, I suppose that would be classed as 'equipment' and bonding to the cpc would be needed. Am I right about this?

(A long way from my original question about metallic baths , I know, but this is what happens when I start reading the regs.!)
 22 January 2013 09:25 PM
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AJJewsbury

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What I am thinking is if the switch is outside the room, the wiring is above the ceiling, the transformers (SELV) are above the ceiling and only the lights are in the location, then no connection to the cpc would be needed. Now, if the switch is inside the location, I suppose that would be classed as 'equipment' and bonding to the cpc would be needed. Am I right about this?

That sounds right to me!
- Andy.
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