Washing machine drum gave electric shock

[TJT]

Hi

First post, although I have been known to lurk here in the background occasionally!

OK, I'll try to give all necessary information, so this may be long... sorry!

The other day I was unloading my washing machine, and got a shock from touching the drum. It was very gentle - more like a friendly tickle than a shock. But seriously I was concerned so I unplugged it and had a look into things.

The machine itself has an electronic program selector rather than the older mechanical clicking type. You turn the dial to the program you want, a red LED starts flashing, and then you press go. ANYTIME the machine is 'on', even before you press go, the drum is live. It wasn't like a static unload.

Normally I'd turn the switch to 'off' before opening the door, therefore the drum is safe to touch. So the machine could have always done this, but I've only just noticed.

OK, so what did I do? With my limited electrical knowledge I see two problems. Firstly, earthing. Secondly, why is there a voltage at the drum?

I looked at the wall socket, and as I suspected there is no earth (old houses here in Argentina rarely have earth). So I plug it into a new socket with earth which I installed myself for my welder, and the problem is fixed. So, I now know that with a proper earthed connection I won't get a shock. Before I use the machine again I'll put an earth to the appropriate socket. I will be re-wiring the whole house next year anyway.

BUT (and here comes the part I still don't understand), I would assume that the drum should never have any current going to it anyway. Is there still a fault with the machine?

I unplugged and took off the back and looked underneath for loose cables or whatever. Everything looked perfect. Extremely neat and tidy, nothing looked at all out of place (I am not an expert in washing machines, but all cables were neatly tied and routed away from the drum area). Nothing broken or loose.

I then tried plugging it back into the UNearthed socket. Still gives a tingle when touching the drum. Using a multimeter I measured voltages, against the neutral wire coming in from the plug. Obviously voltage between live and neutral is between 220 and 230V, standard for here in Argentina. Here comes the weird bit: Chassis to neutral gave about 40V. Drum to neutral also about 40V. The outer casing has white paint, so there was no voltage there.

So basically, when the machine is earthed everything is fine. When it's not earthed most internal metal parts have some voltage. The machine is connected through an RCD, which didn't jump at any point, even when plugged into the earthed socket (probably not enough 'lost' current).

Does it sound like there's a problem with the machine? Or would it be normal for an unearthed machine to have some parts with a voltage? It seems that the earth may be covering up a problem with the machine, but visually it looked perfect.

Hope this made sense. Sorry for the stupidly long message!

Any comments welcome.

Cheers,
Tristan

 

[Space cat]

The hidden capacitor strikes again!

There's nothing wrong with your machine. The problem is caused by something which, quite possibly, isn't shown on any circuit diagram. Any two conductors placed next to each other, but not touching, form a capacitor which will allow AC current to flow. In your case, the capacitor could be an actual component built into a mains filter or it might be formed between wires running around inside the machine or even between wires and the chassis itself.

This hidden capacitor will be small so the current is low but you can still feel it. (I have no problem detecting leakage currents in equipment that's passed a 7 megohm insulation test. Metal surfaces have a curious 'rubbery' feel.) When you connect a proper earth you shunt this tiny current away and the voltage on the metalwork drops to zero.

I strongly recommend that you ALWAYS use an earthed socked for equipment that has an earth connection. If your machine developed a real fault - like a live to chassis short in its motor or heater - you'd get more than just a tingle!

 

[TJT]

Fantastic. Thanks for your answer.

I will take an earth to the socket and will have clean clothes once again!

I'll be rewiring the whole house soon anyway, with proper earth connections. You'd be amazed at the state of the wiring in this house. Lots of it is still using the old fabric-sheathed cables. There are two circuit breakers for the entire house. Lots of cables passing loose across walls etc. At least someone at some point had the sense to install the RCD. I'd love to see a UK inspector's face!

Thanks again.
Tristan

 

[karona]

Lurked for a while, but signed up to reply to this thread, as dodgy Bulgarian electrics nearly killed me.
I had exactly the same problem, small shocks off the kitchen appliances. My power arrives via overhead cables, live and neutral, and neutral is tied to earth at the supply poles, so I've only two wires coming in and no separate earth. I measured the voltage between the exposed metal on the washing machine and the floor of the kitchen, and got 50 volts AC, which is technically enough to kill!
The first step was to ban bare feet or slippers in the kitchen, then I ran a 10mm earth cable from the neutral block in the fuse box to an external earth spike hammered into the ground beside the house. There's now no voltage on the appliance bodies, but you're still not allowed in the kitchen with bare feet. I can only assume that there's a resistance in the earth path back to the supply poles, enough to leave a residual 50 volts floating on the neutral.

Cheers
Keith

 

[viewer]

Keith No you have connected the neutral which carries the current effectively to the surface of all your appliances. If anything went wrong with your neutral (inside or outside the house) the earth would act as neutral and everything would become live. The floor voltage is dangerous (how did you get the reading - floor to earth rod?) Please disconnect as soon as possible.
The earth must go from earth pins/connections/CU/ to the earth rod and kept separate from the neutral.
If you can get a RCD where you are, then one should be fitted. Have a look at the Forum FAQs and / or Google for type of supplies which will explain more.[/u]
It is common in Eastern Europe to find combined neutral/earths after the meter, (in UK always before called PME) but must always be before the CU main switch - it should never be possible to 'turn off' the earthing arrangements.

 

[TJT]

Sorry - I'm the original poster and I was going to report back here once things were fixed, but I completely forgot.

I installed an earth cable for the washing machine (to an earth spike) and the problem is now fixed.

Many thanks to everyone who posted.
Tristan