Author Topic: Checking if an outlet is earthed with a multimeter?  (Read 6360 times)

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Offline XOIIO

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Checking if an outlet is earthed with a multimeter?
« on: July 03, 2014, 10:45:01 am »
Hey all, the little "site wiring fault" is on, on the UPS that I use for my PC in the house we moved to, I remember there was a way to check if an outlet is earthed with a multimeter, but I can't recall what it was, just resistance between neutral and earth or something?

Just don't want to wreck my meter doing this (It's a uni-T 71 series, and they say not to go over 30v AC. The scientist in me wants to try it, but the rest of me stops me since it was fairly expensive lol)

Offline Wytnucls

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Re: Checking if an outlet is earthed with a multimeter?
« Reply #1 on: July 03, 2014, 12:15:11 pm »
Meter selection on Vac. Probes between line and ground wires should show line voltage for a properly grounded outlet. Neutral to ground should of course read 0 volts. (That's assuming the house wiring complies with regulations)
Might be safer to check that ground wires are installed, with a connection to a common earthing ground pin.
« Last Edit: July 03, 2014, 12:23:00 pm by Wytnucls »
 

Offline djococaud

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Re: Checking if an outlet is earthed with a multimeter?
« Reply #2 on: July 04, 2014, 06:45:31 am »
If only one Outlet is dodgy, you can just test continuity beween two outlets earth pins (use an earthed extension cord if needed)... ;)
 

Offline justanothercanuck

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Re: Checking if an outlet is earthed with a multimeter?
« Reply #3 on: July 04, 2014, 07:21:26 am »
You might also get the "wiring fault" light if the poles are reversed.
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Offline G7PSK

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Offline Lee697

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Re: Checking if an outlet is earthed with a multimeter?
« Reply #5 on: July 04, 2014, 08:06:25 am »
I had a fuse box replaced once, and some wiring redone, afterwards, the sparky clipped a lead to the cold tap connection, then trailing a long test lead went and probed every earth socket in the house for continuity.
 

Offline Kjelt

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Re: Checking if an outlet is earthed with a multimeter?
« Reply #6 on: July 04, 2014, 08:13:48 am »
If you have a good working 35mA switch off residual-current device (RCD), or residual-current circuit breaker (RCCB) in your installation you can properly test the outlet with a (well isolated) circuit that flows for one second 40mA from the mains connector to the earth connector, for instance a relay with a power resistor capable of handling this current/voltage and power in a well isolated box.
If the socket is correctly connected and properly earthed the RCD will trip, if not, nothing happens.
 

Offline German_EE

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Re: Checking if an outlet is earthed with a multimeter?
« Reply #7 on: July 04, 2014, 01:41:07 pm »
"afterwards, the sparky clipped a lead to the cold tap connection, then trailing a long test lead went and probed every earth socket in the house for continuity."

Now THAT was a man who was worth the money!

To answer the original question. If your meter only goes to 30V AC then borrow or buy one that goes to at least 600V. You should measure line voltage between Live and Neutral and also between Live and Ground. If you see more than 2V or so between Neutral and Ground then you may have a fault.

PLEASE TAKE GREAT CARE WHEN MEASURING MAINS VOLTAGES
Hold the two meter probes in one hand and put your other hand into your pocket. Never work on mains circuits when you're alone.
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Offline rsjsouza

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Re: Checking if an outlet is earthed with a multimeter?
« Reply #8 on: July 04, 2014, 04:11:30 pm »
If you use an outlet tester, just be aware of the issue reported by the article below:
http://ecmweb.com/contractor/failures-outlet-testing-exposed
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Offline G7PSK

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Re: Checking if an outlet is earthed with a multimeter?
« Reply #9 on: July 04, 2014, 05:27:43 pm »
A good reason for ring mains as a single mis-wired socket would blow the fuse or trip if wired hot to ground, I supose it dose not preclude some clown totally mis-wiring the whole ring.
 

Offline XOIIO

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Re: Checking if an outlet is earthed with a multimeter?
« Reply #10 on: July 04, 2014, 06:26:39 pm »
If you use an outlet tester, just be aware of the issue reported by the article below:
http://ecmweb.com/contractor/failures-outlet-testing-exposed

So, would that be indication of a wiring fault? lol.

I thin I will grab a socket tester, though on ebay Canada they don't pop up when searching, there is an amprobe #ST102A for $16 or so when you factor in shipping.

edit: found one a bit cheaper so ordered it, couple bucks cheaper.
« Last Edit: July 04, 2014, 06:29:19 pm by XOIIO »
 

Offline Neilm

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Re: Checking if an outlet is earthed with a multimeter?
« Reply #11 on: July 04, 2014, 06:39:00 pm »
A good reason for ring mains as a single mis-wired socket would blow the fuse or trip if wired hot to ground, I supose it dose not preclude some clown totally mis-wiring the whole ring.

That happened to me at work. The place had been rewired after arsonists set fire to one of the adjacent units. We moved back in and I was assembling a prototype unit. Every thing worked then I connected the Earth. Touched the case and got a shock. The whole row of units were mis-wired. As they were owned by differnet people, insured by different companies and had been fixed by another firm the arguments on who was to blame took months to resolve.
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