washer fault issue?

[ezzzekiel]

customer had recieved a shock from washing machine, had a look today and there was around 50v between washer and sink top.
checked bonding, rcd trip times, circuit zs all came back fine so why the shock? washer appeared quite rusty and corroded around base but rcd never tripped, apartfrom an internal fault on the washer i cant see how the shock occured without disconnection any thoughts anyone?

 

[telectrix]

measure resistance between washer casing and coldwater pipe, and from there to MET . could be poor earthing on the machine.

 

[ezzzekiel]

Already did mate and it was high, just got me wondering as to why rcd tends to trip out as soon as you look at them but not when they need to

 

[telectrix]

leakage current <30mA. if you get that earth fault resistance path down to an acceptable value, then the RCD probably will trip.

 

[ezzzekiel]

So washer ( obviously seen better days)
Would need earthing improved to create a better fault path to make it trip so the fault is of insignificant value to cause harm

 

[Marvo]

If you're getting a shock from an appliance you're looking for two faults. Firstly theres an insulation fault that's causing a path between the live and the chassis. Secondly there's an earth fault that's allowing the touch voltage of the chassis to rise. Finally the RCD would be a candidate for a thorough testing as well.

There could be a possibility that the sink and tap is at a higher voltage than 0v. This would indicate bonding issues plus a fault causing the leakage (maybe waste disposal motor etc).

 

[topquark]

Is it possible that the PD at the sink is betwen another circuit (not served via the RCD) and the earth bond of the washing machine. I'd check the earth bond of the machine and IR between live+neutral combined and earth (to see if the machine has a fault, or if you're looking elsewhere for an explanation).

 

[ezzzekiel]

So poor earth on washer (installation tested) allowing voltage on casing to rise but what's the limiting factor holding it at around 50v

 

[topquark]

So poor earth on washer (installation tested) allowing voltage on casing to rise but what's the limiting factor holding it at around 50v

Not quite. My suspicion is that the 50V PD is higher on the sink (due to a fault elsewhere) and the body of the w/m is at 0V. I think if you PAT test it it'll possibly turn out fine (which would then explain why there's no sign of the rcd tripping ... as it's circuits line/neutral are still in balance).

 

[Marvo]

....but what's the limiting factor holding it at around 50v

Input resistance of the testing equipment possibly. You'd probably get a much lower reading with an analogue (or higher reading with a digital if you used an analogue)

 

[ezzzekiel]

Not quite. My suspicion is that the 50V PD is higher on the sink (due to a fault elsewhere) and the body of the w/m is at 0V. I think if you PAT test it it'll possibly turn out fine (which would then explain why there's no sign of the rcd tripping ... as it's circuits line/neutral are still in balance).

Tested between sink and microwave etc but got nothing as I suspected that first

 

[topquark]

The only other thing I can think to try is between sink and the earth terminal that the w/m is plugged into (with an R2 unit so you don't have to touch the socket outlet). If the PD is then gone (but reappears when the w/m is plugged back in, it's a machine or plug fault). As any faulty socket would manifest the problem with an R2 unit plugged in.

 

[ezzzekiel]

Will have a bit more of a look in morning see if I can find anything else

 

[ezzzekiel]

Not getting it cant see how 50v is developing across the washer to sink, whats holding the pd between the two around the same

 

[Marvo]

The way to go is to run a trailing earth wire from the main earth at the CU or another known good earth. Check the earth first wrt the neutral at no-load, it should be @ <1v, then use this trailing wire as a reference and check the voltage to the various items such as the sink, washing M/C etc. Once you've established which is sitting above 0v you can start finding out why.

 

[Tonkatoy27]

Customer wearing nylon knickers?

 

[ezzzekiel]

or maybe mine :}

 

[needasparks]

Am i reading this fault correctly as just because there is a PD on the earthing does not mean an rcd will trip as it is not a fault.

 

[topquark]

Am i reading this fault correctly as just because there is a PD on the earthing does not mean an rcd will trip as it is not a fault.

Yep quite correctly, it depends where the PD (and eventual current) has come from. Just coz it's returning via the earth on the w/m (or possibly the sink ... yet to be determined) won't make the RCD trip.

 

[needasparks]

Thats the reason IMO omitting bathroom bonding just because of rcd protection i personally don't like.
I've had many a zap off induced voltages on pipework and no rcd would have stopped them, one of which i measured at 120volts