One for the electricians - 'live' dishwasher

[t8hants]

My wife said she thought she had got a mild electric shock when touching the interior of the dishwasher and the s/s sink simultaneously. So armed with my multimeter and no other skill, I set the dial at 20v and sure enough I got a reading of about 0.3v, very low, but a reading non the less. The toaster, cooker and extractor hood didn't register at all, only the dishwasher. So is this an early warning sign the dishwasher might have a developing fault and may need to go?

 

[Trevanion]

No electrical expert, only speaking from experience but this sounds like a dodgy earth problem.

More here: https://www.ukworkshop.co.uk/forums/can-feel-electricity-in-my-lathe-t117802.html

 

[HappyHacker]

I doubt that 0.3V can be felt. 9V from a PP9 battery can be felt across you tongue but very few can feel it from their hands even when wet. Also most modern meters have a high impedance which means that they can show voltages that are there but are at such a low amperage they would not be dangerous. Also meters can show voltages from the capacitive pickup from a nearby mains cable.

The problem could be one or more of a number of issues:
Incorrect or no bonding of water supply,
Fault in wiring of circuit supplying dishwasher,
Fault in dishwasher,
Fault in other circuit coupled with one of the above,
Or even static electricity

There may also have been another fault that was not apparent at the time you did the measurement and your wife actually got a shock from a higher voltage.

Tracing issues like this can be time-consuming and there may in fact be nothing wrong but I would tell your wife not to touch the metal internal bits of the dishwasher at the same time as the sink.

I would also suggest getting a good electrician to look at it.

I went to one job where the owner was getting a shock from the washing machine. My meter showed about 100V between the washing machine and earth. Tested the washing machine and it was fine, tested the wiring and the earth pin was at 100v to the supply earth, started testing at various accessories and taking things to pieces. The fault disappeared. I have no idea what was wrong or what I did to fix it but lots of further testing showed no fault on the wiring and I have never been called back.

Kevin

 

[pcb1962]

I would suggest that you get an RCD device like this https://www.amazon.co.uk/OAONAN-Adapter ... B01N1P9YFQ and plug the dishwasher into it.
If it trips when you turn on the dishwasher you have a potentially dangerous fault.

 

[Eric The Viking]

The advice on RCD is very good. Use a good piece of wire between Dishwasher casing and sink to try to trip it (and wear gloves just in case). I would also run an extension cable from another part of the house, and use the EARTH on that to measure the dishwasher against (in case there is something wrong with the sink or the whole kitchen's grounding).

. . .

We are so used to digital multimeters nowadays that nobody has much regard for impedance and the way these things work:

Impedance is the AC equivalent of resistance, the only difference being it usually varies with frequency (of the AC). You could alternatively think of resistance as a special instance of impedance. But I digress slightly...

In the old days when meters had needles that waggled, the coil in the meter had an impedance, and needed some current flowing to make any sort of "voltage" measurement*. The finer the wire of the meter coil, the higher the impedance, and the less flowing current was necessary (generally speaking).

Modern digital multimeters (DMMs) tend to have huge impedance (when measuring voltage) and tiny currents flow (almost nothing at all). This can give you truly weird readings sometimes. In particular, DMMs can show "dangerous" voltages where there's nothign dangerous in practice. An example is getting sparks from a comb or hairbrush in the dry winter mornings - the "static" electricity can be high voltage, but there isn't enough charge on the brush to cause a dangerous current to flow. That said, you can still feel it, and a DMM should show quite a high voltage, although probably only for a moment or so. I have heard of people being killed by electricity whilst playing golf (especially in Florida**), but never from brushing their hair!

This is NOT to say your 'leccy system is OK, but that you have to do a bit more than just apply a meter to be sure it's safe. Testing with an RCD cutout is a really good idea, as a starting point. Also you are assuming that the dishwasher is at fault, and not something causing the sink to float up to a higher voltage than ground. Admittedly my money is on the dishwasher, but you have to be systematic and careful when checking this stuff.

Too much info, per usual, but it might be helpful.

E.

*Moving coil meters can't measure voltage directly, but they measure the current through a given resistor and use Ohm's law to get the voltage. DMMs in contrast, pretty much measure voltage (over-simplification I know). It does lead to different readings in the same conditions though, so you need to understand if you use both types. DMMs can't measure current directly, so they measure the voltage across a known resistor (over-simplification!).

**Lightning strikes: If you also account for Alligators, apparently, Florida is a dangerous place to be a golfer.

 

[Racers]

My money is on a poor earth in socket/ wiring and a mains filter in the dishwasher leaking AC through the capacitors to earth.

It needs checking out as a fault could increase the voltage to a fatal level.

Pete

 

[sunnybob]

Your multimeter should have an "omega" sign for ohms. Set to the lowest ohms setting and test the two leads together first, you should get zero, or very close to zero. Remember that number, then stick the prongs onto bare metal on the dishwasher and the earth prong on the 13 amp plug. You should get the same number within 2 decimal points. If its higher, your dishwasher lead and or connection inside the machine is faulty.
You can go all around the house checking your earth connections by probing the retaining screws on the surface plates. and those screws to bare metal on any machine. Any reading higher than a couple percentage points needs to be checked. any reading over 0.5 (after deducting the reading you got from the leads themselves) is dangerous. If you get an infinite reading anywhere, double check your connections and if its still infinite, stop using that circuit and call an electrician.

 

[porker]

Checking from the surface plate retaining screws will only work in metal back boxes where the electrician has bothered to connect the earth across. A lot don't bother from the ones I see. It also won't work on dry lining boxes as these are plastic but you can't always tell from the face plate.
I have a clamp meter that measures earth leakage, but I agree with the previous posts that it may be an earth fault on the socket. IME washing machines tend to leak a small amount to earth as mentioned earlier but when the earth is faulty on the socket that current goes through you when you touch a metal sink which should be bonded to earth on the pipework. Either way it needs fixing. You can get inexpensive socket testers that can often show what the fault is by simply plugging them in and looking at which LEDs light up. Some electricians don't like them because they can't show all faults but they can be useful as a quick check.

 

[sunnybob]

All wall socket screws are connected to earth. If you look on the back of the plate the metal earth band extends to the screw holes.
Doesnt matter in the slightest whats behind the socket. If you cant get an earth reading off that screw then something is wrong.

 

[Marineboy]

All wall socket screws are connected to earth. If you look on the back of the plate the metal earth band extends to the screw holes.
Doesnt matter in the slightest whats behind the socket. If you cant get an earth reading off that screw then something is wrong.

Not so for all sockets. I've just looked at a spare single socket I have and one screw hole is earthed, the other isn't.

 

[dzj]

"I would also suggest getting a good electrician to look at it. "
+1

 

[porker]

Must admit I hadn't ever realised this. I was looking at some light switch fittings just before (which don't). Some of my mains faces (the older ones) only have one side connected also. The new ones are both.

 

[t8hants]

Just an update on my 'little' problem, after a busy weekend away from things, try as I might I can't get the dishwasher register anything on my multimeter now, even with combinations of other domestic appliances working or not. What ever the fault is it is very intermittent and the weather has remained the same throughout - the dishwasher is 'dead', long may it stay that way.

 

[sunnybob]

If you want another dishwasher.... dont read any further :shock: :roll:
But over 50% of faults are in the 3 pin plug and or mains lead. =D> =D>

 

[sammy.se]

Couple of points from me:

1/Dishwashers sometimes 'flood' on the inside bottom tray - due to leaks or overflows or who knows what.

My Bosch has a little 'check water' light that comes on when this happens. I wait a day, and it goes away. Or, I tilt the dishwasher and it goes away. I don't like it and I don't understand it... But that's what happens. Maybe your intermittent situation is due to water leaking inside and bridging a circuit.

2/Meile have an outlet store - amazing deals on top quality stuff, and you can get the full warranty (grade A B and C products have different warranty terms).

If you are going to buy another one, please do check it out. You can genuinely save 50%+ on Meile products, making them another choice against other brands. I have a Dryer and washing machine, saved £1000 and have the 10 year warranty.

https://m.miele.co.uk/domestic/outlet-2243.htm#

 

[sunnybob]

The "check water" sensor is seeing water where it shouldnt. wait for it to evaporate, or tilt the machine so the water runs somewhere else, and the light goes out.

You SAVED a grand on two items :shock: :shock: :shock: :shock:
I'd want a lump of change for a grand on two items :roll: :roll:

I had a "friend" here who started moaning about their dishwasher burning out elements and it was the councils fault for keep turning the water off. I heard about it after the THIRD element was fitted. He was on the point of suing the council when I carefully pointed out to him that his dishwasher element should not come on unless it sensed water was present :roll: :roll:
New dishwasher required.

 

[sammy.se]

The "check water" sensor is seeing water where it shouldnt. wait for it to evaporate, or tilt the machine so the water runs somewhere else, and the light goes out.

Thanks Bob - that's been our strategy to deal with it! no idea why it is happening though :-(

You SAVED a grand on two items :shock: :shock: :shock: :shock:
I'd want a lump of change for a grand on two items :roll: :roll:

It sounds extravagant, but it really isn't We use our washing machine at least once per day (kids in the house).
I spent what I considered 'reasonable' money on two washing machines in 10 years: approx £300 per washing machine, twice, on what I thought were decent brands (Whirlpool, Zanussi). After the second one went, I researched Bosch (my go-to brand for home appliances, including the above mentioned dishwasher) - and the good machines were coming in at £300 -£400, and reviews ranged from 3 to 7 years life.
Miele outlet: £500, incl a 10 year warranty, large size, plus excellent performance - it was a no-brainer.

Same logic goes for a dryer - a good Bosch etc ~£300 - £400. Miele, £500.

The way I see it, I paid £100 extra for each machine, and for that I get 10 years of guaranteed service and a great quality product.

 

[sunnybob]

Sammy, its only humour, but I like it :roll:

we have a bosch washing machine, bought the expensive "built in" model 11 years ago when we moved here. Only to find the kitchen fitter couldnt work out how "build in" and had made a giant cupboard for it instead.
Its done umpteen thousand washes ( many visitors, grandkids for the whole summer holidays every year, etc etc), and the only problems are when the missus leaves her hair pins in her pockets and stops the pump impeller from turning. But I know a man who can fix things :roll: .
The same kitchen fitter, when presented with the built in dishwasher (a Kupperbusch, which is apparently a cheap brand bosch, but that has also worked for 11 years straight), handed the matching panel to me, said "these things give me headaches" and left.
And the final nail in that same kitchen fitters chances of ever working for me again was when he had to put the hob extractor in.
I ended up standing on the worksurface, showing him how to secure it into the wood surround because he really didnt have a clue.
My Mrs quite liked him, untill after sawing lots of wood just outside the kitchen door he said "I'm finished now, sorry about the mess" and left , NEVER to be called back. :roll: :roll: (hammer) (hammer)
The "sorry about the mess" line is still used regularly, but it gets me nowhere.

 

[sammy.se]

Ah, looks like the good grace you have had with the life of your appliances, is traded off against the kitchen fitter 's erm... skill set :-D

I like in a very hard water area - I suspect it might have something to do with the life expectancy, but I have tried additives like calgon, with no luck... ho hum things could be worse

 

[sunnybob]

When I had to earn a living in England, I installed and serviced (among many others) combi steaming ovens, like you see in all those top chef programmes. Oh boy, the crap inside those oven steam tanks. If you saw it you would never eat there.
Mostly it was brown sludge, but Bath and surrounding areas in Somerset was the worst area. within a week soft white chalk would collect on the heating elements and stop it working properly. I used to fit water purifiers to stop it happening, but the shops were so stupid tight they wouldnt buy replacement cartridges for the filters, so every month they had to call me in and I spent hours (at £70 an hour) descaling them. Stupid "£$%^&*(.

We are lucky here, the kettle is at least 2 years old and the inside looks like new.