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Topic Title: shocking sink
Topic Summary: Have I missed anything so far?
Created On: 11 April 2013 03:11 PM
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 11 April 2013 03:11 PM
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esspeegee

Posts: 127
Joined: 06 January 2008

Hi all,
Customer complains they have been getting shocks from the sink and the dishwasher so I went to look.
Poor condition kitchen exemplified by a rotten and sagging work top behind the sink and drainer. Obviously a lot of moisture getting behind the units. Can see lots of copper underneath the plinth all green and grotty. Evidence of damp I think. Circuit is protected by 30A fuse wire and theres no RCD.
I measured 70V between the sink and the dishwasher. When I turned off the switched fuse to the dishwasher the voltage disappeared and remained near zero when I measured the pd between the sink and cooker circuit cpc and kitchen ring cpc. I didn't think to check if the sink was bonded but if isn't I'm not sure bonding would be the right thing top do because surely the voltage shouldn't be there in the first place.

I couldn't get the dishwasher out to check the outlet connections so have arranged for the customer to do so. In the meantime I have isolated the dishwasher from the supply and put up a warning notice on the switched fuse. I decided that in all probability the problem is damp or a loose cpc connection in the outlet connector. But if it is neither of these things, should I recommend they get someone look at the dishwasher or just bond the sink?
Thanks
Simon
 11 April 2013 03:24 PM
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bartonp

Posts: 49
Joined: 28 September 2009

You could get ~70-80v just from an appliance 'floating' up due to filter capacitors on the mains. Need to know if there is any 'oomph' behind it... (tech term)
 11 April 2013 04:16 PM
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tattyinengland

Posts: 784
Joined: 23 November 2006

The only way to come to decision of any sort is to check the circuit:

R1+R2
IR
Visual inspection of the cable (Where ever possible including inside the switch fuse(s) and sockets)
Ze
Zdb
Zs

Make a decision.

I'd certainly recommend an RCD at the very least even if the circuit was seemingly perfectly fine, with the full knowledge that they're likely to go for it as they want to stop getting shocks and this might be caused by damp in an area you cannot see and may pass the tests on the day you do the tests if it is fairly dry - the dryer having been off for a while.
 11 April 2013 04:28 PM
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AJJewsbury

Posts: 11427
Joined: 13 August 2003

You could get ~70-80v just from an appliance 'floating' up due to filter capacitors on the mains.

But presumably the dishwasher is class 1 - so should be earthed rather than floating.

Sounds like a broken c.p.c. either inside the dishwasher, its flex, or fixed wiring.

Classic situation where metal pipework/earthed bonding carries dangers not present with all-insulated plumbing (although there'll always be a danger to another earthed class 1 appliance).

- Andy.
 11 April 2013 05:14 PM
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Jaymack

Posts: 4638
Joined: 07 April 2004

Originally posted by: esspeegee
Obviously a lot of moisture getting behind the units. Can see lots of copper underneath the plinth all green and grotty. Evidence of damp I think. Circuit is protected by 30A fuse wire and theres no RCD.

What is the wiring type? VRI cables in conduit?.

Regards
 11 April 2013 05:37 PM
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SKElectrical

Posts: 910
Joined: 01 February 2009

Check earth at source, 'Main' earth.
It's no good saying you cant get behind the d/washer. All you've done is left it guessing and you need to get behind it at some point. You have to charge high and inform there may be surface d├ęcor to be repaired. Otherwise you end up discussing it and thinking about it without getting anywhere.
I would check other outlets' voltages L-N (or Ze). If they are okay then suggests fault with outlet behind washer.
Get some gloves and pull it out. If they don't want you to do that then wish them well.

Nasty job.
 11 April 2013 05:38 PM
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esspeegee

Posts: 127
Joined: 06 January 2008

PVC T&E. The spur that isolates the dishwasher is in the kitchen ring final and has a Zs of 0.54.
 11 April 2013 05:40 PM
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daveparry1

Posts: 6200
Joined: 04 July 2007

I think Andy has the answer to this one, the dishwasher is not being earthed, most likely poor earth connection in the fcu i'd say,

Dave.
 11 April 2013 05:43 PM
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daveparry1

Posts: 6200
Joined: 04 July 2007

Zs 0.54
Sounds like the fcu has an earth then so probably broken earth connection inside the machine. Do a continuity test between the machine frame and the point where the earth connects to the fcu.
 11 April 2013 07:05 PM
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tillie

Posts: 788
Joined: 03 May 2006

Hi esspeegee , can you not test the casng of the dishwasher to confirm if it is earthed.

Regards
 11 April 2013 07:25 PM
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mikejumper

Posts: 1714
Joined: 14 December 2006

Originally posted by: esspeegee
I decided that in all probability the problem is damp or a loose cpc connection in the outlet connector.

To feel a voltage on the sink or dishwasher my guess is it's possibly more than just damp; you may have water resting across terminals or a JB.
 11 April 2013 11:31 PM
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alancapon

Posts: 5765
Joined: 27 December 2005

I agree. It is probably a lack of an earth connection to the dishwasher. Most of these devices have surge suppression on the incoming mains, which will result in the case sitting about half mains potential if you disconnect the earth.

Regards,

Alan.
 12 April 2013 11:30 AM
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mikejumper

Posts: 1714
Joined: 14 December 2006

Originally posted by: alancapon
I agree. It is probably a lack of an earth connection to the dishwasher. Most of these devices have surge suppression on the incoming mains, which will result in the case sitting about half mains potential if you disconnect the earth.
Alan.

To have a voltage appear on the diswasher chassis unless it's earthed seems an odd design.
How good does the earth have to be?
Wouldn't a high Zs TT earth act as another potential divider across the suppression network?
 12 April 2013 05:05 PM
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daveparry1

Posts: 6200
Joined: 04 July 2007

Nothing odd about it Mike, most class 1 appliances will have a small amount of earth leakage present especially where motors and surge/spike suppression capacitors are fitted,

Dave.
 13 April 2013 04:21 PM
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Zs

Posts: 2897
Joined: 20 July 2006

esspeegee, you have a more detailed pm from me.

I had similar last year and am seeing the property in my mind. Not a nice job and stressful as the anxious client watched over all the time. Dealing with this kind of thing on a rewireable is not easy.

In my case it was socket circuit not a dishwasher. Three days until I found the melted connector block under a floorboard where a spur had been added. They were hard-up, I did not want to leave them unsafe and it cost Zs dearly but was sorted.

So, I advise caution, the screwdriver in the lawn method and a concise discussion about your hourly fees right now.


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