Extraneous Conductive Parts in Bathroom

[Midwest]

Currently doing a kitchen refurbishment. When doing the quote, peering under the kitchen sink, noticed bonding to water was 4mm, and same for gas. Property has a TNC-S supply, and had replacement CU in 2010 (no certs available). Said to customer bonding should be upgraded to 10mm. Easy cable route, which customer decided to run himself (ex electrician) and I will connect & test, jobs a goodun.

So I turn up before kitchen fitters to do my first fix. The customer has done good job of running bonding cables and has removed old kitchen floor units around incoming water pipe, to reveal it's plastic. Now next bit is not my point (so lets not debate that!), no probs cable not wasted, connecting to household copper service, will comply with reg. 528.3.4.

Connect and test gas & water bonding. Gas fine but water giving reading of 19 odd ohms. Further removal of old kitchen units expose section of plastic push fit, between kitchen copper pipe and adjacent downstairs toilet copper. Starting to think its a pointless task, customer is adamant the rest of the house cold main etc, is in copper as he had refurbished said downstairs toilet.

Now for some reason, I decided to test Extraneous Conductive Parts in the bathroom. A piece of copper to toilet, copper tails to flexi-hoses to basin and metal radiator with copper tails. Reading I obtained on tails, using my MFT IR test, was 0.01Mohms (tests carried locally be between circuit cpc and ECP's). Bathroom has electric shower (on RCD) and light (on MCB only).

Now from reg 415.2.2 and the helpful vid by Chris Kitcher, I understand (lets keep it simple with the shower), any reading below 1667ohms doesn't need bonding, above 1667 & below 0.02Mohms does, and above 0.02Mohms is just a piece of metal (metal rad was >532Mohms).

My question is, is the above paragraph correct, and if so, what would you advise the customer on the bonding of the extraneous conductive parts, i.e. the copper tails?

The copper tails are no more than 300mm long. I'm kinda erring on the side of ignoring them! Bathroom was refurbished 2 years ago, walls & floors tiled. All downstairs CH pipes give very low readings, as do the pipes entering ceiling below bathroom, so guess push fit used in bathroom refurb'.

 

[tony mc]

If a new CU was fitted in 2010 I take it that all ccts are RCD protected so as long as main bonding is in place supplementary bonding in the bathroom may be ommitted

 

[Midwest]

If a new CU was fitted in 2010 I take it that all ccts are RCD protected so as long as main bonding is in place supplementary bonding in the bathroom may be ommitted

Lighting not on RCD.

 

[HappyHippyDad]

Omission of supplementary bonding is dealt with in reg 701.415.2

You have to meet all of the following conditions in order to omit supplementary bonding:

1. All final circuits must comply with the requirements for automatic disconnection according to Regulation 411.3.2
2. All final circuits of the location must have additional protection by means of a 30 mA RCD in accordance with reg 701.411.3.3
3. All extraneous-conductive-parts of the location are effectively connected to the protective equipotential bonding according to Regulation 411.3.1.2 (i.e R<1667Ω)

So if the lighting in the location is not on an RCD you cannot omit supplementary bonding to an extraneous-conductive-part.

 

[Midwest]

Omission of supplementary bonding is dealt with in reg 701.415.2

You have to meet all of the following conditions in order to omit supplementary bonding:

1. All final circuits must comply with the requirements for automatic disconnection according to Regulation 411.3.2
2. All final circuits of the location must have additional protection by means of a 30 mA RCD in accordance with reg 701.411.3.3
3. All extraneous-conductive-parts of the location are effectively connected to the protective equipotential bonding according to Regulation 411.3.1.2 (i.e R<1667Ω)

So if the lighting in the location is not on an RCD you cannot omit supplementary bonding to an extraneous-conductive-part.

Thanks HHD for typing all that out, I couldn't be *****. In my scenario the resistance is too high (& not high enough!) for RCD to operate within time, I believe (ignoring lighting circuit for time being, which for 415.2.2 is R< 1.67).

 

[Midwest]

Sorry HHD, that should of been a Thanks, corrected now.

 

[Leesparkykent]

If the copper tails are joined on with plastic elbows, couplers, etc then they aren't extraneous conductive parts.

 

[Midwest]

Nope, copper out of floor to rad, toilet & basin.

 

[Leesparkykent]

Nope, copper out of floor to rad, toilet & basin.

did you test the pipework just after the joint in plastic?

 

[Midwest]

did you test the pipework just after the joint in plastic?

Nope, can't get to that at the moment. All the plastic push fit is going to be replaced under the sink anyway, so will re-clamp it then. Not sure if that's going to resolve the issue in the bathroom though. I'm also not sure about relying on the accuracy of my MFT IR test, giving me 0.01Mo when I want 0.02Mo, i.e. the reading could be 0.019, but my MFT will not display that?

 

[GEOFF S]

Hi

keep it simple, if its less 22k Ohms its extraneous so bond it. So water and gas are bonded, are there any other extraneous parts entering the building, if not job done.

So if the location meets the 3 requirements as mentioned by hhd above then all is good.

Cheers

 

[Midwest]

Take you advice re keeping it simple. Three pieces of pipe are extraneous then. Gas is extraneous (bonded), water is not (but bonded, or will be for reg. 528.3.4.), no others.

Location does not meet requirements of 701.415.2, v) & vi) - using 415.2.2.

Tiled floors & walls, earth cable & clamps. :yesnod:

 

[Lucien Nunes]

I'm also not sure about relying on the accuracy of my MFT IR test, giving me 0.01Mo when I want 0.02Mo, i.e. the reading could be 0.019, but my MFT will not display that?

This is not about accuracy but about resolution and readability. The reading has a certain percentage accuracy for the actual measurement, then plus or minus a certain number of counts due to the way the display works. If that happens to be 4 counts (a typical specification) then even with supreme accuracy 22kΩ could still display as anywhere between 0.00 and 0.06 MΩ. Your 0.01 MΩ reading could thus indicate a solid connection or a part that is not extraneous - you genuinely can't tell and must use an alternative meter.

 

[Midwest]

This is not about accuracy but about resolution and readability. The reading has a certain percentage accuracy for the actual measurement, then plus or minus a certain number of counts due to the way the display works. If that happens to be 4 counts (a typical specification) then even with supreme accuracy 22kΩ could still display as anywhere between 0.00 and 0.06 MΩ. Your 0.01 MΩ reading could thus indicate a solid connection or a part that is not extraneous - you genuinely can't tell and must use an alternative meter.

From your reply, I think you're saying that using my MFT IR test with the reading obtained in this instance, is not a suitable device to confirm whether the pipe work is extraneous or not?

 

[Lucien Nunes]

Yes, would be helpful to know what MFT it is, but I'd say you need to be able to read to a resolution of say 1k or better to use it for that test.

 

[Midwest]

Megger 1730, realise not the most suitable device to use for this measurement, but it's never been that much of an issue before. Normally such readings of 'non' extraneous conductive parts, have been several Mohms.

 

[Midwest]

Time to purchase a new continuity tester, perhaps, with some longish test leads!

 

[mattg4321]

Only skim read this but is the resolution of your MFT not much better on continuity setting rather than IR settings. Think my 1553 measures up to 99k ohms on continuity.

Might be wrong though - it is friday evening!

 

[Midwest]

Hmmmmm, my 1730 spec shows Continuity/Resistance ranges; 0.01 - 99.9 ohms + 100 - 99.9kohms. As far as I can see, my maximum reading on my Continuity setting is 99.9omhs. Anyhows, a reading of 99.9kohms would convert to 0.0999mohms, so we're in the same boat, as regards the limitation of this device, to accurately read 22000ohms.

 

[Lucien Nunes]

The 1730 appears to be autoranging on resistance and on the higher range with a max reading of 99.9kΩ it reads in increments of 100Ω +/- 2 counts. At 22kΩ it would display somewhere between 19.8 and 22.2 which is fine for your purposes. A separate discussion is the relative merits of different test voltages for this test.