Washer/dryer humming noise, potential between piping and earth, normal? - Page 1
Forum section: electronics / general

author: Scintillo
author_rank: Newbie
timestamp: September 02, 2020, 02:37:28 pm
content: I was alarmed by "electric" humming noise in my bathroom. I tried unplugging my washer/drier and sure enough that stopped the noise. As I've seen similar things happen with speakers when there is noise in the ground, I did a random measurement for potential between the bathroom piping and electric ground.I found around 0.5 V of (AC) potential. Is this something normal? Shouldn't both of these be the ground? I measured conductivity and found around 300 ohms of resistance between them.Now the noise is gone and I can no longer measure any potential.

author: paulca
author_rank: Super Contributor
timestamp: September 03, 2020, 05:12:07 pm
content: If by "electric ground" you mean Neutral I measure nearly 2V AC difference between Neutral and Earth at any plug socket. There are dozens of threads on how the neutral get's grounded to Earth and where.If you measured 300Ohms between an Earth on the appliance (like any exposed metal) and a clean copper plumbing pipe, then you might have a dodgy bonding somewhere which can happen when you have plumbing modifications without the bonding being redone.If you measured 300 Ohms between the mains Earth and the mains Neutral, I would throw that value out as the neutral is carrying current and measuring resistence in an energised circuit is fraught with problems as the meter uses a small voltage to measure the resistance via ohms law. Further I would suggest sticking your meter into the mains while it's energised on the "Ohms" setting is probably dangerous.

author: TimFox
author_rank: Super Contributor
timestamp: September 05, 2020, 03:40:56 pm
content: There is another post here where somebody smoked his DMM in "continuity" mode by accidentally probing mains. The fuses only protect the current modes in normal DMMs.Seehttps://www.eevblog.com/forum/beginners/multimeter-cheapie-fried/

author: Siwastaja
author_rank: Super Contributor
timestamp: September 05, 2020, 03:51:01 pm
content: Do you have a residual current device (RCD) installed? If not, I highly recommend getting a simple plug-in unit likehttps://www.biltema.fi/rakentaminen/sahkoasennustarvikkeet/vikavirtakytkimet-ja-vikavirtasuojat/vikavirtakytkin-2000030602. This will catch most deadly faults and has been mandated in new electrical installations in bathrooms for quite some time and is a good voluntary add-on in older installations.There exists no thing called "electric ground". In old installations, PE (protective earth; yellow-green; the two exposed contacts in the socket) is usually tied to the plumbing with low resistance. But if you use plastic pipe for example, not every faucet is earthed, obviously. Neither the piping nor PE should carry much current. There can be a significant voltage difference between N and PE, though, because they are tied together further away, but N carries current, hence voltage drop on N wire, but not PE wire. Both N (neutral) and L (line) are called LIVE wires and considered equally dangerous. Try to avoid home-brew/lazy terms like "ground" or "earth" because they are common sources of confusion and danger.

author: Scintillo
author_rank: Newbie
timestamp: September 26, 2020, 12:12:30 pm
content: Quote from: paulca on September 03, 2020, 05:12:07 pmBy "electric ground", I meant the ground connection on the electrical socket (not neutral). And yes this was 300 Ohms between the ground in the socket and the piping.Quote from: TimFox on September 05, 2020, 03:40:56 pmThanks for the warning but I was measuring between socket ground and piping ground.Quote from: Siwastaja on September 05, 2020, 03:51:01 pmThis is a pretty newly built apartment building (2015 or so I think). So I would think there is GCD on all bathroom sockets. I think the pipe here is supposed to be ground as there is a path (although with 300 Ohm resistance) to ground. I was not touching neutral in socket here.