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I'd recently been given an EMF meter and when I turned it on, the EMF around most of the house was around 15 head height. If I'm downstairs and raise it to the ceiling it's well above 100 and the same upstairs putting it towards the floor. Now this is a bit worrying as we've been living in this house for the last 16 years but not only that I've recently had kids and where my 3-year-old sleep's he's being pummelled with 20 gauss.

I'd turned all power off at the fuse and proceeded to remove fuses to narrow down which circuit was causing the high levels. My first thought was it must be the light circuit as it was the roof and floors that had the highest readings but it turns out it was the outlet circuit that's causing the issue.

I've done some research and found that a neutral wire returning via a different live wire can cause this to happen and is in fact quite a common issue.

So my question is where and how is it best to start to find where that neutral wire has gone astray?

I'm currently in the process of getting our old fuse box replaced with a newer version. So thought now would probably be a good time to look into getting this sorted. Thanks for your help in advance.

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  • How old is your house? Does it have any knob-and-tube wiring?
    – A. I. Breveleri
    Feb 11, 2016 at 21:23
  • If there is a load on the circuit it will have a higher value. if you think it is a bad neutral or coming back on a diferent line invest in a amp clamp meter. you can measure each hot and neutral pair coming into the pannel they should have the same reading. A fluke T5-600 meter cost ~ 100usd and will measure your household voltages and currents it even has a ohm meter to 1K ohm. I believe you will probably find the circuit in question is loaded more than the others causing the feild you are measuring.
    – Ed Beal
    Feb 11, 2016 at 21:25
  • I'd say it's around 40-50 years old. It's not knob and tube wiring. I'm pretty sure it's conduit wiring although I can't be sure if that's true as I've not had the floor boards up to have a look.
    – The Angry Saxon
    Feb 11, 2016 at 21:27
  • I'll ask this one, based on your profile, are you based in the UK? I don't know much of the wiring there, but the 'ring' circuiting can cause high levels due to the variance in wiring allowing the current to travel from either end of the main. I.E. This creates the imbalance because the current gets to pick it's own line and might not be canceling out correctly.
    – TFK
    Feb 11, 2016 at 21:30
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    Are you sure you don't mean milligauss? 20 gauss is strong enough that it would be magnetizing most of the ferrous metals in the house. I'm also not sure I'd be concerned about health effects - EMF at 50hz (UK line frequency) has an extremely low ionization potential. I'd be a lot more concerned about your electronics.
    – Comintern
    Feb 11, 2016 at 23:52

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That's a big job. I had to sort out a bunch of wiring in an old factory which had a lot of neutral problems. I shut off service to the building and, at the panel, "pulled off" one hot and neutral off each circuit and did a series of diagnostics, checking for resistance between it and the rest of the neutrals, and resistance between the hot and neutral, and hot and other neutrals - alternating whether night-lights were plugged in or not. If anything seemed out of the ordinary I followed it to the next junction box and carefully troubleshot, and the next, and so on until it tested clean. (this was a real mess as many circuits were MWBCs.) I don't recommend this, but I also had a 120v extension cord coming from another building, and connected the pulled-off circuit to that, and sniffed for voltage being anywhere it should not. I would not recommend doing that with 230v, that stuff bites hard.

It can help to install a GFCI breaker (UK: RCD) in your panel, as they will trip if there is any cross-neutral activity between circuits. You can move it around from circuit to circuit. Likewise you can put GFCI outlets on any point in the branch circuit, which will protect everything downstream. In fact, many service panels have an outlet right next to the panel, and you could install a GFCI in there, attach a hot and neutral wire to the "load" side, and use that to test each circuit in turn. I wish I had thought of that in hindsight!

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  • Thanks for the insight and I may wait till we have the RCD installed with the new fuse box before I go delving too deep then. Not massively overjoyed with the opening sentence of it being a big job thought :P Would earthing not done correctly on a circuit cause high EMF? From what I understand as long as the neutral runs back with the live wire earthing doesn't really effect the EMF?
    – The Angry Saxon
    Feb 11, 2016 at 22:45
  • Wires with no current should not have any magnetic flux. There won't be any current on the earthing wires unless there is a ground fault, so it should be a non-factor. Occurred to me you have a gauss detector... You might be able to narrow it down greatly by turning off one circuit at a time. (All my work was in steel conduit.). This thought too: UK style ring circuits still work even with 1 break in hot and neutral, but in between the breaks, current will flow in opposite directions.
    – Harper - Reinstate Monica
    Feb 11, 2016 at 23:25
  • Yeah -- it's good that you get this sort of stuff fixed; while the health implications of magnetic field exposure are unclear, split/looped neutrals also carry more immediate implications in the form of induction heating of ferrous parts and 50/60Hz EMI to sensitive devices within the field (heard any humming from your speakers lately?)
    – ThreePhaseEel
    Feb 12, 2016 at 3:43
  • Okay so update time. I spent Saturday finding what circuit was causing the issue. Narrowed down the sockets that were on that circuit and then checking each of them over for any fault in the way they had been installed. I did find an earth and live wire had fused together in on socket which I have resolved and thought that that must have been it but to no avail. Found some sockets had loose wiring which I re-sitted but none of it made any difference. Lifted some floor boards to see if I could see anything obvious but again nothing.
    – The Angry Saxon
    Feb 15, 2016 at 10:30
  • I'm calling electricians today to get the fuse box swapped over to a decent one with a RCD and talk about a possible re-wire. We have an extension that has sockets on the "bad" circuit, so I'm almost guessing it was something that they'd done when pulling the circuit from the house into there.
    – The Angry Saxon
    Feb 15, 2016 at 10:34

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