Shocks In Kitchen

[alchemist]

Hi All,

A customer has called to say they are getting shocks off their kitchen tap, outside tap (adjoining to kitchen) and exposed metal parts of kitchen appliances e.g. dishwasher and toaster.  

They only get shocks with bare feet touching the ground.  Also, only turning off the main switch on the CCU stops it, turning off individual circuits does not.  If I remember correctly, it's a split board with two RCDs and the incoming isn't on an RCD. 

I haven't visited the house yet, but can I run through what i'm thinking and get your thoughts?...

Firstly, if the taps are live and they need bare feet on the floor that tells me that their pipework and earth conductor on their kitchen sockets are not actually earthed - maybe the conductors are disconnected at the CCU or the incoming earth is damaged or disconnected?  They have only had this problem relatively recently, I put some new sockets in the house about a year or so ago and there were no issues at the time.

So, i'll check the main earth is connected at the CCU, that there is bonding on pipework, and make sure the earth conductor is connected at the CCU for downstairs sockets.  

Secondly, there must be a leak to earth somewhere, probably on the kitchen circuit.  So i'll check the voltage on the metalwork and unplug each appliance to see if that gets rid of the problem, if not, i'll IR test the circuit to see if it's a wiring fault.

Thanks

Mike

 

[ProDave]

I would be thinking PME supply with a dodgy (on the brink of failing) neutral?

Check Ze and PSCC

 

[Evans Electric]

Mike , as you know it could be anything but go for the Immersion Heater first .

On many Split Load Bds  guys didn't put Imm.Htrs on the RCD side .....don't ask me why . :C

 

[NozSpark]

+1 to both the above

 

[alchemist]

Thanks both, it didn't really occur to me that the fault could be on something outside the kitchen but not causing disconnection - the RCD for the sockets only picks up a difference between live and neutral doesn't it, so I guess the earth on the sockets downstairs could be live but not trip anything.  Likewise with the pipework, leakage won't trip anything.

It is odd that they get shocks still though, as the pipework should be earthed and so 0v between that and the floor - still must be dodgy earthing somewhere/anywhere/everywhere.

 

[Andy™]

similar to a job a few years back, shocks from anything metallic downstairs

upstairs flat dead short L-E, TT, no RCD. but being refurb'd so all class II and plastic pipes, so they didnt have any problems

 

[alchemist]

Dave, wouldn't the neutral failing show other problems, like appliances not working due to reduced supply voltage?   

 

[ProDave]

I'm thinking high resistance neutral so as loads are drawn, neutral (and earth) rise WRT true earth.

Yes if you are astute you might see the lights dimming as loads are drawn.

The touch voltage is not (yet) very high as they only notice it with bare feet.

Certainly something to check, I may be barking up the wrong tree.

Last PME neutral failure I saw, the DNO ended up digging up the guy's drive and a lot of the street to lay a new cable in. 

 

[alchemist]

I'll post the test result, i'm going there on Saturday.  Thanks again for the advice.

 

[Robin Spark]

Did some pa testing in offices recently and the ladies were getting shocks off the sink, been going on for so long they have placed a rubber door mat by the sink thinking it might stop it to no avail.

Well they never asked me to look at it (officially)and they still havent paid me for pat work done, so only way i am going back is if i can check them for nylon underwear to rule out static

 

[pewter]

My friend had the same problem.

DNO came out and it was his overhead 2 wire supply. Neutral had gone down and due to the suppliers PME connection it made the bonded pipework the return path.

 

[Evans Electric]

Just re-read your OP .... I see its a dual RCD board  so every circuit is RCD protected ?    That makes it a bit worrying .

 

[ProDave]

Just re-read your OP .... I see its a dual RCD board  so every circuit is RCD protected ?    That makes it a bit worrying .

Making it more likely to be a DNO issue with high impedance neutral, raising the earth potential above true local earth.  The fault current, to true earth would be coming from the input to the CU, hence the RCD doesn't see it as an imbalance.

We eagerly await finding out what it really is.

 

[Evans Electric]

Looking that way Dave ...unless the RCDs are US .

 

[SLIPSHOD & SLAPDASH]

I had  the same fault many years back. Amazingly i had worked at the property  2 days  when the builder said its my turn to make the tea, then shouted out 'dont touch the sink or w/machine the same time as the kettle'.  The fault was the kitchen fitted had drilled through a radial circuit feed to the local sockets whilst fixing a wall cupboard. The cpc was broken but the wall was very damp and over the years it started arcing out to the damaged live and the voltage started rising. I assume the same fitter, rather than trace the fault had stripped the tw&e feed & cut the cpc under the floor.

 

[Evans Electric]

I had similar at a betting shop once .     Staff being thrown across the tea room from the sink .

Sink was ceramic , waste was lead, oversink water heater had a fault to earth .     Back at the board the two legs of the ring were showing red and black for the last foot and the earths were just left out . 

 

[davetheglitz]

I had a similar problem - but in this case the earthing and bonding was fine.However the washing machine had been operated without the waste pipe connected and although the top of the vinyl flooring was dry to touch it was swimming below - and the contaminated water had come in contact with the live terminal of a junction box. There was around 90v between the floor and earth when measured with a voltage indicator. In this case there there was no RCD - but probably the resistance would have been too high to reach 30mA to cause a trip.