shock from water pipe

[JACKC]

Asked by friend at work for some help which is an area I don't get involved with much as a maintenance engineer with little domestic experience. He has moved a washing machine into new position and whilst leaning on it, he touched the water pipe and got a small shock. Didn't think much of it until whilst under the sink he touched water pipe again and nothing else, he got bitten again. Suspect he has a bonding issue on the water but he says it has an earth cable on it. How would you advise going about fault finding this as it must be a common problem. I do have access to test equipment at work, but would like some advise on what to check first.
Many thanks

 

[Lectrician]

I would suspect two issues.

1. Lack of earth to the property if a TN system, of faulty main RCD if a TT system.

2. Fault on a circuit causing a L to E fault of low impedance.

 

[JACKC]

Thanks for that. Apparently its a TT system but the rcd doesn't trip. From what you say then it is a circuit fault AND rcd, as if pipework is providing fault path the rcd should detect this. If I was to put a voltmeter on pipework and to earth stake and say got 60v. By then isolating each circuit in turn until voltage goes, this would be the one to rip apart for fault or should I confirm the bonding is 0.05 ohms before anything else.

 

[electronicsuk]

It would seem worth testing the earth rod for a start, it may not be doing its job, and also (as you suggest) checking pipework bonding back to MET is low impedance. Just because an earth looks to be connected at either end, it doesn't necessarily equal continuity.

 

[JACKC]

Thanks, will check ELI and then go from there.
Thanks again.

 

[ericmark]

If TT how old? Some old systems had voltage v-ELCB and the earth goes through the device as a result parallel earth paths can disable it. These should all be replaced with a c-ELCB or RCD as it is now called.

Earth rods need only have a 200 ohms resistance although around the 20 to 60 ohm is more common. However with parallel earth paths one often gets a reading of a few ohms with ELI meter.

Do remember the test button on a RCD only tests the mechanics in case they stick you need a RCD tester to test it and this will test at 1/2 setting to show not too sensitive then full setting to see it trips and 5 x full to see if within 40ms and all repeated for Pos and Neg cycle.

A shock can be felt with very little current and if the earth rod is disconnected you can get a shock from the filters used in IT equipment so ensure earth is connected first or you can be looking for non existent fault. Old houses often relied on water pipes and gas pipes for their earth and as the utilities became plastic so the earth was lost which is now why you are not allowed to use them as the main earth. So check there is an earth rod.

Earth faults are normally tested for with power off. And all items unplugged and switched off with a insulation tester which normally uses 500 volt to measure resistance with. All circuits should be over 1Mohm.

 

[Spark123]

This would be the one to rip apart for fault or should I confirm the bonding is 0.05 ohms before anything else.

The main protective bonding is worth checking, along with the Ze (or Ra) and the operation of the RCD. If the RCD has a greater than 30mA trip you don't need to do the 5x test.

 

[JACKC]

Thanks for the tips, will borrow the Megger 1553 in the next few days and suggest a visit.

 

[Click-Sure]

Earth rods need only have a 200 ohms resistance although around the 20 to 60 ohm is more common.quote]

NICEIC permit 100 ohms as a minimum.

Lets make our own regs.

 

[Taylortwocities]

NICEIC permit 100 ohms as a minimum.

.

Did you mean minimum?