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puppymartini

20V AC between slab and electrical ground (lemmy.ca)

submitted 2 weeks ago by [email protected] to c/electricians

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I've just had a new house built in Atlantic Canada. This morning I noticed a bit of a tingle from my coffee machine when I touched it with wet hands. The machine has a grounded (3 pin) plug and I checked - it has 0V between the parts I touched (the entire metal outer case) and the ground socket in the outlet. So, I got curious and did some more measurements. It turns out there is 20V AC (and about 300mV DC) between the ground in my outlets and me when I'm standing on my floor (sealed concrete slab) with bare feet.

I assume this isn't good?

I'll be calling the electrician that wired the house in the morning, but I'd appreciate any insights you might have.

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[–] [email protected] 9 points 2 weeks ago* (last edited 2 weeks ago) (1 children)

There obviously shouldn't be any voltage between ground (in your socket) and ground (through your body) - a tiny amount of static build up is possible, but that should disappear instantly.

Switch off all the breakers, then check switching one at a time. Your most likely culprit could be a washing machine, a fridge, that sort of thing.

Just be methodical, switch everything off & check, one after the other, that way you'll isolate the issue to a single circuit. Then unplug whatever is on that circuit and check again to clear if the problem is in the appliance or in the circuit itself.

Then of course don't open / peak / try anything yourself.

You know that right?

[–] [email protected] 2 points 2 weeks ago (1 children)

I turned the whole house off at the main breaker. I still have around 20V (it varies - sometimes it's as low as 14, I've seen it as high as 27) between my slab and the electrical ground. I also turned off my well pump, that's powered from another building, and it made no difference.

[–] [email protected] 1 points 2 weeks ago* (last edited 2 weeks ago) (1 children)

Having gathered more info from your other replies, well, let's say the same but quicker... you know the meme :

'xcept here it'll be GROUND ALL THE THINGS!

The slab, the pipe, the Cat6 conduit, ground it all. If I was in my line of work, there'll be a 6mm² ground wire between both houses.

(Image credit Allie Brosh' excellent "Hyperbole and a half")

[–] [email protected] 1 points 2 weeks ago (1 children)

The slab, the pipe, the Cat6 conduit, ground it all...

The Cat6 is not in conduit - it's direct burial rated cable. It was a bit of an afterthought - I already have a pair of Ubiquiti GigaBeams that are working very well. But, the trench was being dug for the water line so I jumped on Amazon and bought a cheap cable. I ran it my desk as a fly lead for a while to make sure it worked and then dropped it in the trench before it was back filled. If fixing my ground issues doesn't fix the ethernet performance I'll just go back to the GigaBeams.

..If I was in my line of work, there’ll be a 6mm² ground wire between both houses.

I might actually be able to achieve that - there's a 4 wire "well pump wire" from my new house back to the well, which is very close to the old house. One of those wires might be a ground and if so, it might make sense to ground it at both ends. I'll look into it.

[–] [email protected] 2 points 2 weeks ago

When I said 6mm² it's because of the distance, you want more copper to get less resistivity between both grounds; your water pump probably run on 1.5 or 2.5² which isn't much - but by all means, please ensure that pump is grounded!

Also because IRL I run elec for open-air festivals & with great responsibility comes great paranoia ;)