Author Topic: Faulty mains grounding?!  (Read 2738 times)

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Offline casper.bang

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Faulty mains grounding?!
« on: July 05, 2013, 12:12:55 am »
Inspired by the Electric Shock thread, I wonder if people on this forum would know about household electric stuff (I have great respect for 230VAC stuff and only play with < 12VDC).

So anyway; sometimes when I shower while the dishwasher is connected to (230VAC) mains and touch the hot/cold nob, I can feel quite a tingle. The DMM can pick-up around 35-45VAC. I say sometimes, because it's not always reproducible for me, which is why I have not called anyone yet but just disconnect the dishwasher when I don't use it.

I do wonder what could possible be going on though. I'm fairly confident the problem is isolated to the dishwasher. I'm also fairly confident that the grounding connections are in order all the way from the machine back to where mains enter my house (I inspected all plugs and switches).

So I guess my question is; should this be happening if my grounding is in order (get a new dishwasher) or is there by definition an issue beyond the dishwasher (faulty grounding). I suspect the last case is the correct one, so perhaps the grounding speer outside my house, in the ground, is covered in rust or so and only works properly when the soil is wet (which could explain the sporadic nature, not always being reproducible).

I should mention, I live in Denmark where 230VAC@50Hz is used, and house installations consist of 10A fuses and residual-current fault devices (I can only assume, mine doesn't trip because it's an older kind and/or the current is too small). How would you go on "debugging the issue"? Any hints appreciated. :)
 

Online richard.cs

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Re: Faulty mains grounding?!
« Reply #1 on: July 05, 2013, 12:32:15 am »
It shouldn't happen with any faulty appliance if your grounding is correct, but the RCD is probably ignoring it because the current is too low.

Do you mean you get a tingle off either tap, or only if you hold both? UK practice is to create an equipotential zone where all pipes, electrical stuff, etc is bonded together so whatever voltage it floats to you can't tough anything conductive at a different voltage (and yes I know the requirements for this have been relaxed recently). Where did you measure between with the DMM? Measurements between taps, between each and your electrical ground, to anything else conductive in the bathroom (eg metallic waste pipes), and also from your mains ground to true ground (stick a screwdriver in the soil a few yards away from the house and measure between your mains ground and this) would all be useful. Preferably measure with and without the suspect dishwasher.

Do you know what kind of earthing system your house uses? Usual options are earthspike in the ground, water pipes, combined with the neutral and separating at the meter, or seperate cable (or metallic cable sheath) back to the substation.
 

Offline Paul Price

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Re: Faulty mains grounding?!
« Reply #2 on: July 05, 2013, 12:56:04 am »
If you unplug the dishwasher and the tingle disappears when standing in the shower, then the Dishwasher ground is being connected to a cold water pipe that has been probably spliced into PVC so all the water pipes in your home are floating. You need to check the ground wire on the dishwasher going to whatever wrong place it is connected to.

If you get a tingle standing in the shower, then the sewer pipe is connecting your feet to ground through water and the water pipes in the shower are not grounded correctly.

If you unplug the dishwasher and you still get a shock, then the problem is somewhere else in you home/building where someone else has tied the water pipes to some white appliance and everybody showering in the building is getting a tingle.

In all cases, it means the water pipes in your bathroom are not grounded and should be.
 

Offline G7PSK

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Re: Faulty mains grounding?!
« Reply #3 on: July 05, 2013, 01:07:25 am »
Is plumbing plastic pipes, I have come across similar with a power shower unit, all the plumbing is plastic pipe from the power shower to the shower head both hot and cold, the shower is over a plastic tray but the drain is metal and bonded to ground, the shower pump developed a fault in the earthing circuit, so standing in the shower normally caused no problem but touch the drain and you got a good tingle, the induction motor induced sufficient voltage into its case and impellers that the water was conducting it to the shower head. If your dishwasher is not earthed and you have plastic pipes which of course are not earthed either the water can conduct well enough to get a shock.
 

Offline casper.bang

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Re: Faulty mains grounding?!
« Reply #4 on: July 05, 2013, 01:27:05 am »
Very interesting... particular the comments about plastic pipes. My house generally has all-metal piping and appliances are grounded. However, I think I remember seeing that the pipes in the wall, going to my shower, were fixed at some point; leading me to suspect this *could* be plastic.

That might explain why it's the only place I see a voltage buildup at the shower faucet (measured between the dials and the metal drain in the floor). What I don't understand is, how can a (slightly faulty?) dishwasher, supposedly sufficiently grounded (though getting water through a plastic tube), induce voltage in a shower faucet 10m away?

Could this be a combination of the electricity moving through the water, building up around the faucet, dissipating when I touch it (providing a ground) but not enough to make the RCD trip? And in this case, only thing I can do is to somehow try to ground the faucet through other means than the hidden (plastic) pipes?
 

Offline Jon Chandler

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Re: Faulty mains grounding?!
« Reply #5 on: July 05, 2013, 03:59:30 am »
Rather than continuing to test this with your body, I suggest either using a voltmeter or calling an electrician.  Since you are even posting questions like this, I suspect the electrician is the proper answer, and I would do it with some urgency!

Yes, it's only an intermittent tingle...apparently through your heart ( hand to hand on the valve handles or hand to foot through the drain).  Since it's intermittent and not understood, it's not worth betting your life on whether it might go from slight to deadly.
 

Offline bilko

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Re: Faulty mains grounding?!
« Reply #6 on: July 05, 2013, 04:49:44 am »
From what you are describing it sounds like your house earth connection is not connected to ground. You become the ground connection when you get in the shower. I would take advice already offered and get a qualified electrician in to do a proper earth test on your installation.




 

Offline Paul Price

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Re: Faulty mains grounding?!
« Reply #7 on: July 05, 2013, 04:54:38 am »
Cassper.bang, you say,"Could this be a combination of the electricity moving through the water, building up around the faucet, dissipating when I touch it (providing a ground) but not enough to make the RCD trip? And in this case, only thing I can do is to somehow try to ground the faucet through other means than the hidden (plastic) pipes?"

And the answer is no, to the "building up around the faucet" question and yes to the other questions.

The current is continually flowing from the mains filter capacitors through you, and likely harmless, bothersome,  and not building up like water in a dam.

The idea is to ground the dishwasher to some earth ground, but don't tie a wire to your metal gas line going to your stove.
 

duskglow

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Re: Faulty mains grounding?!
« Reply #8 on: July 05, 2013, 05:20:56 am »
Thank you for giving decent advice Paul.  Nonetheless, OP, please call an electrician.  Again, that's what they're paid for.
 

Offline casper.bang

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Re: Faulty mains grounding?!
« Reply #9 on: July 05, 2013, 06:17:57 am »
I can't very well call an electrician unless I can replicate the problem for him to see. Until I observe it again, I play it safe and disconnect the unit (only runs once a week) - but meanwhile I'd still like to try to understand what's going on, which is why I post here. :-//
 

Offline c4757p

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Re: Faulty mains grounding?!
« Reply #10 on: July 05, 2013, 06:18:55 am »
I bet he'd have a good idea where to look for the problem even if it's not active at the moment.
No longer active here - try the IRC channel if you just can't be without me :)
 

duskglow

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Re: Faulty mains grounding?!
« Reply #11 on: July 05, 2013, 06:25:15 am »
Agreed.  No electrician worth his license is going to say "oops, I don't see the problem, call me when you see it."  He'll run some tests and probably figure out the root cause pretty quickly.
 

Offline casper.bang

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Re: Faulty mains grounding?!
« Reply #12 on: July 05, 2013, 07:08:20 am »
I just tested continuity between radiator (ground) and the shower knobs, and theres no connection (there is though between radiator and sink faucet). Ok I'll call soneone.
 


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