I'm exploring the capabilities of my cheap Aneng SZ08 multimiter, which I've recently purchased. I have a question related to the detection of a neutral line in the wall socket using a multimiter. What are the ways of doing this? I've seen a video of a Russian guy on the YouTube who connects one of the probes to his central heating pipe (which goes down to the Earth ground), and he plugs the other probe to one of the outlets of the socket. If the meter reads 220v, it is phase, otherwise it is neutral. Does this method work and is it safe?
2 Answers
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General disclaimer: Call an electrician if you are in any doubt. Mains electricity is lethal and not to be played around with.
I use the same method if grounded outlets are not available. With the advent of PEX pipes (plastic) allowed for installation in some countries (at least for water supply), it's no longer guaranteed. If you know what you are doing and you measure 230 V between one socket in your wall outlet and 0 V on the other with respect to your central heating pipe, I would switch over to resistance measurement and check resistance between heating pipe and your assumed neutral. If low ohmic, you are good.
You can probably encounter edge cases where your central heating pipe is only close to zero volt compared to earth. I have tripped my RCB by measuring the current between the ~1 V central heating and outlet neutral.
Mains outlet checkers are available commercially which will tell you which is live and which is neutral with basically you as earth reference, bleeding say 1 uA though you.
Here is one example. Since it does not detect neutral/earth swap, I don't think its smart enough to use you as external reference.
Image curtesy of Conrad.
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\$\begingroup\$ So, as I understand, touching your central heating pipe with one of the probes while other is in the outlet is safe and it won't energise the pipe? \$\endgroup\$– GogCommented Nov 1, 2023 at 17:47
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1\$\begingroup\$ @Gog Assuming your multimeter isn’t an unsafe piece of garbage and you use the V outlet in it, then yes. Your multimeter should be 1 Mohm or more. \$\endgroup\$– winnyCommented Nov 1, 2023 at 18:00
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\$\begingroup\$ alright, I got it that I'd better not try it. \$\endgroup\$– GogCommented Nov 1, 2023 at 18:06
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\$\begingroup\$ Please buy a proper multimeter. You will have use for it for the rest of your life. \$\endgroup\$– winnyCommented Nov 1, 2023 at 19:18
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As you were told in answers to your other question on the cheap Aneng SZ08 multimeter, it is unsafe to use it to measure mains voltage. It is unlikely to be properly rated to handle mains voltage safely, whatever the CAT classification on the front of it says.
That said, if you had a suitably rated meter, then measuring between an earth, of which a central heating pipe ought to be a good example, and a socket terminal, would be a satisfactory way of telling which terminal was live and which neutral. You would not be surprised to find a few volts on neutral with respect to earth.
