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Topic Title: Earthing a cast iron bath
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Created On: 12 July 2018 12:07 PM
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 12 July 2018 12:07 PM
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deleted_1_vstrom1000

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Edited: 25 July 2018 at 10:34 AM by IET Moderator
 12 July 2018 12:32 PM
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tattyinengland

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There's no need to supplementary bond a bath unless perhaps it had a metal waste pipe going into the ground; in which case bond the waste pipe.

Under normal circumstances, It has, and cannot have, a potential fault path.

Bond the taps if necessary, (assuming there are no plastic bits in the line) bond the waste pipe if necessary. Don't bond the bath.

OR - ensure all circuits in the bathroom are RCD protected and you can leave the supplementary equipotential bonding out all together.

An addendum to the above: See reg 701.405.2 for the details of what I've said above (What needs supplementary bonding and what doesn't) and when it can be left out, taking into account (vi) --------assuming that all extraneous conductive parts of the location are effectively connected to the protective equipotential bonding according to reg 411.3.1.2 and the note below (vi)

Edited: 12 July 2018 at 12:42 PM by tattyinengland
 12 July 2018 01:14 PM
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OMS

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Hello, Hello ?

This is the 15th edition calling - can we have our bonding requirements back, please

OMS

-------------------------
Let the wind blow you, across a big floor.
 12 July 2018 01:39 PM
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deleted_1_vstrom1000

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Edited: 25 July 2018 at 10:35 AM by IET Moderator
 12 July 2018 01:52 PM
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OMS

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Have you tested the thing to see if it is, in fact, extraneous - that's a good starting point in any assessment of bonding.

Unless this bath is embedded in a concrete floor with no DPC, has a solidly connected copper waste system or is otherwise connected by means of copper CWS and HWS supply lines then it most certainly won't be extraneous.

If it is extraneous as a consequence of metal to metal contact with the copper pipes, the bonding those pipes, bonds the bath effectively

Alternatively, drill a hole in it and use a brass nut and bolt - give the client a bowl to catch the drips and wrap the connection in Denso tape - you can pop rivet the required label to the bath !!

Regards

OMS

-------------------------
Let the wind blow you, across a big floor.
 12 July 2018 03:24 PM
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deleted_1_vstrom1000

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Edited: 25 July 2018 at 10:35 AM by IET Moderator
 12 July 2018 03:44 PM
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tomgunn

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I thought if you had an RCBO fitted, I know you don't, then you don't requite any supplementary bonding to wet area's??

-------------------------
Tom.... (The TERMINATOR).

handyTRADESMAN

Castle Builders
 12 July 2018 04:31 PM
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OMS

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Only if it's extraneous in its own right - if it's picking up an earth potential from the pipework, then it's already bonded if the pipework is bonded

I think you're mixing up a value which is actually that for the resistance of the joint rather than between component parts of extraneous systems - ie you have no obligation to limit the resistance of bonding from MET to pipe to 0.05 Ohms do you ?

Regards

OMS

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Let the wind blow you, across a big floor.
 12 July 2018 04:36 PM
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Zoomup

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701.415.2

Z.
 12 July 2018 05:40 PM
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deleted_1_vstrom1000

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Edited: 25 July 2018 at 10:35 AM by IET Moderator
 12 July 2018 05:55 PM
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geoffsd

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Originally posted by: vstrom1000

If there was ADS and RCD's, the resistance between the accessible parts would be maximum 50/Ia (415.2.2) e.g. 1.67K ohms using 30mA - the measured path would be via the cpc back to the MET, the main bonding conductor, back to the extr. cond. part in the location (e.g. the metal bath).

Correct.

But there's no RCD's there. Therefore, the resistance between supplementary bonded extraneous-conductive-parts and exposed-conductive-parts should not exceed 0.05 ohms (GN7 2015).

No, it does not say that - or shouldn't.

Without RCDs, it is 50/Ia of the largest OPD. E.g. 50/200A for a 40A MCB - 0.25 Ohms between parts.
I.e. 200 x 0.25 = 50V
Edit - sorry I put / instead of x.

This suggests that if an accessible exposed conductive part measured 0.05 ohms to the bath pipework but e.g. 1 ohm to the bath, then that's not that particular part (the bath) being 0.05 ohms to the exposed cond. part, hence bring it down to 0.05.

Wrong values.
As said the 0.05 Ohms is an accepted level near to negligible for the actual joints - conductor to part.

Of course, the above only applies to parts which actually ARE extraneous-c-ps to the location.

Edited: 12 July 2018 at 06:10 PM by geoffsd
 12 July 2018 07:03 PM
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deleted_1_vstrom1000

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Edited: 25 July 2018 at 10:36 AM by IET Moderator
 12 July 2018 07:30 PM
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OMS

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I'd be pretty certain the 0.05 ohm requirement is to prove the effectiveness of the individual joints, and know the chaps in the long trousers sitting in the smoky room when it was dreamt up - try working out the resistance of a bit of 2.5mm2 copper conductor and see how far that gets you (or doesn't actually)

Apply a bit of ohms law to the problem - what's the voltage drop across 0.05 ohms - and what could it credibly be to reach a safe (ish) potential of lets say, 50V

Regards

OMS

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Let the wind blow you, across a big floor.
 12 July 2018 07:33 PM
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geoffsd

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vstrom:

Then - what is the point of 415.2.2 ?

Also, why not read the actual regulations instead of a book "someone" has written about the regulations?
 12 July 2018 07:39 PM
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OMS

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Are you Zimmerman's sock puppet ?

OMS

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Let the wind blow you, across a big floor.
 12 July 2018 08:00 PM
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deleted_1_vstrom1000

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Edited: 25 July 2018 at 10:36 AM by IET Moderator
 12 July 2018 08:15 PM
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geoffsd

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Originally posted by: vstrom1000

I can see where confusion/differences arise. 415.2.2 speaks for itself, both in the regs and in GN3 2015 pg24. 415.2.2 can also be used to determine the limiting resistance/csa of supplementary bonding conductors (section 8.4, GN8 2015). However, then consider that in section 2.6.5 of GN3 2015 (pg 38) the R2 method can be used to confirm the bonding connection between extr.cond.parts... by connecting the leads of the instrument between any two points, such as metallic pipes, and looking for a reading of the order of 0.05 ohms. the section then goes on to say the 0.05 can be used across joints of e.g. earth clamps. Then there's section 1.5.2 of GN7 2015 which applies to parts, not necessarily joints. Then there's Best practice guide 4, relating to parts, not joints.

I think you read too many confusing publications written by "someone" who might also have got hold of the wrong end of the stick.


In short, if you're in England, it seems a bit like it's take your pick, as 0.05 can only be safer. However, in Scotland, according to a well known training body, we have to apply 0.05 to suppl bonding when ADS, and/or RCD's and/or equip bonding connecting the parts to the MET are not present.

I would say that they are wrong.

Also - if a resistance between two parts is below 50/Ia then they are considered effectively connected (415.2.2) anyway so that supplementary bonding is not required even when there is no RCD.
You are unlikely to achieve 0.05 Ohms between parts.

You acknowledge 50/Ia works for RCDs present but dismiss it when they are not. Why not go for 0.05 Ohms even with RCDs as can only be safer?
 12 July 2018 08:40 PM
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deleted_1_vstrom1000

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Edited: 25 July 2018 at 10:36 AM by IET Moderator
 12 July 2018 10:55 PM
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deleted_1_vstrom1000

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Edited: 25 July 2018 at 10:37 AM by IET Moderator
 13 July 2018 12:34 AM
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mapj1

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I'm not sure, but as OMS and I are similar in age, I'll have stab..
I think a reference to Bob Dylan whose real name is Robert Allen Zimmerman, but who features in a work by Lennon, decrying false gods- being an example of the 'real thing' as opposed to something to believe in - folk worship the derivitive, Bob Dylan, but do not refer to the original
Or that may be so much clap trap, and something else is in mind. - perhaps he will log in and clarify tomorrow.

Only connect and all that.

-------------------------
regards Mike
IET » Wiring and the regulations » Earthing a cast iron bath

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