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Topic Title: Electric Shock while washing up
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Created On: 19 April 2013 10:28 AM
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 19 April 2013 10:28 AM
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adammid

Posts: 48
Joined: 02 November 2010

A colleague of mine has mentioned that they have been experiencing what feels like an electric shock whilst washing up.

They say that it is nothing serious but like a 'slight tingle'.

All of the electrical circuits are protected by RCD.

Any ideas of what may be causing it and any suggestions on how to prevent it from happening.

They have stated that they have had a laminate floor fitted recently and since then they have not experienced it as much.
 19 April 2013 10:37 AM
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tattyinengland

Posts: 767
Joined: 23 November 2006

Does the RCD work? Or is it wired up properly so that the RCD has not been by-passed?

I'd guess this to be the first fault.
Then test the circuits in the kitchen (assuming the washing up is in the kitchen)
 19 April 2013 10:39 AM
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Parsley

Posts: 884
Joined: 04 November 2004

Is it a PME supply and old house with no DPM ? It is possible preceived electric shock due to the floor being at a different potential to the pipework and reduced resistance as the hands are wet hands, due to voltage drop in the PEN conductor of the supply.

The laminate floor is now acting as an insulator.

Regards
 19 April 2013 10:43 AM
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AJJewsbury

Posts: 10964
Joined: 13 August 2003

My guess is the same as Parsley's - try measuring voltage between the sink/taps and true earth (say a long screwdriver shoved into a flower bed), then again between true earth and the MET.

- Andy.
 19 April 2013 10:58 AM
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adammid

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Joined: 02 November 2010

Many thanks. One thought had been a different earth potential but wasn't sure what was causing it. I believe that it is an old house and may not have a DPM.

My colleague has said that an electrician has been round to look and has suggested fitting an earth rod. Not sure how this would prevent the problem???
 19 April 2013 11:11 AM
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AJJewsbury

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My colleague has said that an electrician has been round to look and has suggested fitting an earth rod. Not sure how this would prevent the problem???

There are two possibilities - either keeping the (presumably) PME earth from the electricity supply and trying to pull its voltage down by connecting it to a local rod. Due to the resistance of the soil around the rod that's likely to be ineffective, although it could raise the voltage of the ground in the vicinity of the rod, so if it was close to the kitchen it might reduce the difference between the floor and taps slightly.

The other possibility is to disconnect the installation from the supply earth and use the rod instead - effectively turning into a "TT" system. Depending the state of the existing installation, there might be a need to add some extra RCDs.

I suppose another possibility is that the installation is already TT and a poor earth connection (or even unearthed) and has relatively high earth leakage currents for some reason.

We'd need a bit more information (e.g. earthing type) to be sure.

- Andy.
 19 April 2013 11:13 AM
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Parsley

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You need to find out what type of earthing system is being used.

If it's PME (TNC-S) the electrcial installation is earthed via the suppliers earthing facility and if there's no DPM it might be better to convert it to a TT supply earth rod. This will help with removing the risk of a potential difference between the floor and anything earthed or bonded to the MET.

Regards
 19 April 2013 11:29 AM
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adammid

Posts: 48
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Ok many thanks.

I do not believe that it is a TT system at the moment.

The info that I have is that is a house far from any other dwelling (ie potentially far from the supply transformer) and it is an old house that has many issues with its construction (ie potentially no DPM like you have mentioned)

If an earth rod was installed would you connect that to the MET and leave the suppliers earth in situ or would you recommend disconnecting the suppliers earth. Would the supplier need to be informed?
 19 April 2013 11:30 AM
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Jaymack

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Originally posted by: adammid
They have stated that they have had a laminate floor fitted recently and since then they have not experienced it as much.

What covering was there before?

Regards
 19 April 2013 11:37 AM
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AJJewsbury

Posts: 10964
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If an earth rod was installed would you connect that to the MET and leave the suppliers earth in situ or would you recommend disconnecting the suppliers earth.

First check that our guesses are correct - there are other possibilities - e.g. a local problem with the earthing in the kitchen and a faulty appliance that might give the same symptoms.

I'd suggest disconnecting the supplier's earth - BUT that will almost certainly render fuses or MCBs incapable of providing automatic disconnection in the case of earth faults - so you MUST make sure that everything is suitably RCD protected, and that the rod has achieved a suitably low resistance to earth.

Would the supplier need to be informed?

Not normally.

- Andy.
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