Voltage on Sink (longish read)

[Lee Sparks]

Hi guys,

I wanted to run a scenario by you.

Well, the story goes, friend of my wife

 

[SLIPSHOD & SLAPDASH]

I posted an almost exact same scenario a while back ( no idea where it would be here) In my case the cpc was broken and the earth floating. It was broken when the kitchen fitter drilled through the cable. Damp had got in and over a period of 5 years the voltage rose on the sink and anything on that bit of pipework connected with the damp bit of wall

 

[ProDave]

Well you need to do some tests. Check the ring for continuity, insulation, polarity, R1+R2 etc.

PAT test the dishwasher, or at least confirm continuity from the earth pin of the plug to the case.

And check that pipework bonding.

Measure with a voltmeter from the pipework to the MET see if there's any voltage on any of the pipes

 

[lineman]

I would plug in my tester to a socket and have a wandering lead on the dishwasher door hinge and conduct an Eli test to confirm that the metal parts of the dishwasher are adequately earthed. Could well be a faulty dishwasher causing unstable potentials. Obviously this would be my starting point and then further investigate from there . On reflection pro dave has just mentioned that. My apologies!

 

[philbas]

Just another thought. maybe well of target.

Do they have a nice new nylon carpet that is building up a static charge on them.

Then they touch the sink and it discharges.

 

[SLIPSHOD & SLAPDASH]

On my fault the voltage was 160 ish from the sink to the MET

 

[Evans Electric]

Always suspect the immersion heater , if there is one , before checking elswhere.

On earlier installations and including 14th , 15th and 16th edition jobs the Imm.Htr was often not included on RCD side of split boards .( on mine they were !!)

Because of resistance of water + BS3036 fuses + non RCD , faulty heaters often do not blow fuses. Sometimes a clue can be if client says " Water takes forever to warm up and is'nt that hot"

I've found heaters with just two prongs left in the water and the pipework has a raised potential.

 

[batty]

You really need to get back to basics and test the circuits. I had one on a job like this and this was because the cable to the washing machine had got damaged in the wall so CPC was not connected to socket for washing machine and there was 240 Volts on the CPC so with the washing machine on the sink was at 240 Volts.

 

[SPECIAL LOCATION]

Have any of these 'voltages' actually been measured with reference to incoming earth..

i.e. wander lead to the sink and dishwasher....

For example...

Could be sink @ 0v and D/W @ 60v

or

sink @ 60v and D/W @ 0v

or

Sink @ 30v and D/W @ 30v

Would all give the same apparent fault potential between the two devices...

But need to know exactly whats what...

Remember there is NO specific requirement to supplementary bond sinks or draining boards...

top of Page 43 on-site-guide

You could be introducing a potential difference that wasn't there by bonding. :C

 

[Lee Sparks]

Thanks for the advice, gave me lots to think about.

Once i found out the story with the dishwasher, weather it was faulty or not. I will measure for voltage on sink.

Then determine if the sink pipes are earthed. Maybe the kitchen fitter used plastic push fit things on the additional pipework he installed and didnt maintain bonding continuity?

I havent got a wander lead or long lead for my tester. When carrying out a method 2 long lead test on continuity, could i use an alternative? such as bellwire or something?

I think i will carry out a full test on the circuit anyhow.

Thanks again !!

 

[kme]

You could use a roll of speaker wire; DC cable, 25mm SWA, or anything you`ve got to hand - as long as it conducts..............

 

[Andy™]

When carrying out a method 2 long lead test on continuity, could i use an alternative? such as bellwire or something?

length of 6491x

and to keep it neatly for storage, use an old extension lead case, and put the 6491 in place of the flex

 

[NozSpark]

Lee,

if you haven't got a wander lead just use an extension lead with a plug top wired with a meter or two of flexible earth.

 

[Lillpete]

Also check the boiler control wiring, I've come across it before where a plumber had connected a yellow from an old three core into the earths but the other end of it was connected to the satisfied of the tank stat, so every time the water got hot all the metal work in the house livened up and as there was no bonding the voltages could well have varied around the installation.

 

[SLIPSHOD & SLAPDASH]

, or anything you`ve got to hand - as long as it conducts..............

How about a kitchen sink :innocent :innocent

 

[SPECIAL LOCATION]

Then determine if the sink pipes are earthed. Maybe the kitchen fitter used plastic push fit things on the additional pipework he installed and didn't maintain bonding continuity?

Now... where does it say you need to maintain bonding continuity to a kitchen sink?

:C

 

[Lee Sparks]

lol

Thanks lads!

 

[Lee Sparks]

Hi chaps,

Thought I would keep this updated.

It

 

[ProDave]

I didn’t see an earthing conductor, I didn’t see an earthing conductor coming from the supply sheaf (TN-S) and I didn’t see an earthing conductor coming from the service head (TN-C-S)

So if it has a TNCS service head, and you couldn't see an earth connected to it, why didn't you connect an earth from the earth terminal on the head to the MET?

 

[Lee Sparks]

Access to the service head connections was covered, and two seals were in place.

I didnt know at this stage, what earthing system it was(still dont)

Weather it was missing a earth from the sheaf of the supply cable or an earth from the service head itself.

As far as im aware, im not surposed to mess about with the service supply.

I did take a pic on my mobile of the service head and supply cable on my mobile, ill upload it asap. ( not sure on the quality)

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The 16mm earth is not connected to the sheaf,although it looks like it, its actually connected to the MET, then to the CSU.