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Why does my computer have high magnetic fields - only in certain houses?

Discussion in 'General Electronics Discussion' started by John Jones, May 19, 2019.

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  1. John Jones

    John Jones

    May 19, 2019
    I sometimes use a gaussmeter to measure the magnetic fields around my computer, keyboard, mouse, and headphones.

    The strange thing is that in some houses I've lived, there's virtually no magnetic field at all, while in other houses, there's an extremely high magnetic field around all my peripherals (even though the hardware never changes). Some houses just seem to have really high magnetic fields everywhere, while others don't.

    Does anyone know what causes these strong fields, and is there anything I can do to keep them out of my computer? I don't want unnecessary magnetic fields engulfing all my hard drives (or my body, for that matter).
  2. AnalogKid


    Jun 10, 2015
    Many possible reasons. For example, knob and tube wiring. For an AC power run from the breaker or fuse box in the basement to somewhere else in the house, today we use 3-wire cable which essentially is a long skinny single-loop inductor with a ground path distributed along the run. Old houses have knob and tube wiring. The two wires are about 1 foot apart and there is no earth ground. I've never done any measurements, but for the same loop current (AC load at the outlet), the older wiring *has* to radiate more.

    Also, without knowing the frequency content of the fields being detected, root cause diagnosis is almost impossible.

    John Jones likes this.
  3. dave9


    Mar 5, 2017
    Hard drives often have inductors on their circuit boards which are bound to create a stronger magnetic field due to proximity, than any stray fields present in the room. It is not an issue.

    Your computer contains multiple other inductors and at least one transformer in the PSU. It is the source of the strongest magnetic fields in it.
  4. AnalogKid


    Jun 10, 2015
    The magnetic fields produced within the computer and its peripherals are relatively constant and independent of the ambient environment. As you've already deduced, the changes you are detecting are reflective of the environment, not your computer.

    As for these fields interfering with the computer's operation or corrupting stored data - no. The computer has magnetic shielding around the sensitive components like the disc platters and heads. And, the shielding required to make the chassis compliant with FCC part 15 (B) works both ways, decreasing both emissions and susceptibility.

    As above, the power supply is a significant source of EMI, but it is wrapped in a steel cage (for that reason). And even if it weren't, it would not affect operation.

    John Jones and davenn like this.
  5. BobK


    Jan 5, 2010
    You don’t say what you consider a very high field stregth.

  6. John Jones

    John Jones

    May 19, 2019
    AnalogKid, thanks for the information! :)

    That's reassuring. I had also been concerned about vacuuming too near to my computer tower, but from what you say, I guess I shouldn't be worried.

    Though I still wish there was some way to shield my computer from environmental fields because I must admit I am concerned about sitting with my hands engulfed in magnetic fields all day long.

    It is known that high field strengths (over 100 µT) damage the nervous system. Whether low fields can or can't, I don't know (the jury is still out according to what I've read) but I'd rather not take unnecessary risks if there's a way to shield my computer.

    What I do know is that when I've been using the computer for a few hours in the more "magnetic" environments, I very often get nasty pains in my hands, in the exact places where the fields make strongest contact with my hands (and it has nothing to do with RSI, believe me). I have heard of other people having similar symptoms.

    And then there's headphones. In the same "magnetic" environments, when I've used headphones for a while I've also found I had sharp pains exactly where the headphones touched my outer ear (even at low volumes). This means I actually can't wear headphones in certain environments because I know I'll get pain if I do. I've tried buying many different pairs of headphones and ear buds, but they all gave me some kind of pain, in the places where they came into contact with my ears.

    I am not saying these problems are definitely caused by magnetic fields. I really don't know what the problem is. But I would like to do all I can to be as safe as possible from unnecessary risks.

    Well when I say "high" I am obviously talking relatively…

    "Low fields":
    In some houses I get readings lower than 0.1 mG (10 nanotesla).

    "High fields":
    In other houses, the fields are higher than 4 mG / 0.4 µT. Note that this exceeds regular exposure recommendations by the governments of France, Netherlands, Denmark, Norway, Italy, and Israel.

    [Mod edited ... mG not MG milliGauss not MegaGauss]
    Last edited by a moderator: May 22, 2019
  7. Alec_t


    Jul 7, 2015
    You could avoid using a cell-phone, for starters, but you'll have a job escaping the Earth's magnetic field :).
    davenn likes this.
  8. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    Vacuuming near my computer never caused any problems.
    The issue here seems not to shield the computer from the magnetic fields but your person.
    How do you know that the fields make strongest contact in these places? Magnetic fields are not sharply limited, they extend over some range (size depending on the strength of the field and possible shielding materials like iron).
    Headphones in most cases operate with magnetic speakers, If you are that much susceptible to magnetic fields, avoid using headphones or use electrostatic headphones.

    If the same equipment causes you trouble in one environment but not in another, I'd take this as a strong indicator for the problem being with the environment, not with the equipment.

    While I will not dispute your sensitivity to magnetic fields, scientific evidence for such seems to be scarce at best (Wikipedia). In the light of your different reaction to the same equipment in different environments it may be more constructive to find the difference in benign and malign environments which may have an unhealthy influence on you apart from magnetic fields.
  9. duke37


    Jan 9, 2011
    Are you a good water diviner?

    Ear lobes are a common place for bed sores due to pressure reducing the blood supply. Use headphones which surround the ears not sit on them.
    Last edited: May 22, 2019
  10. AnalogKid


    Jun 10, 2015
    *There* is an excellent topic for a controlled study. Screen for EM sensitivity, then run listening "stamina" trials with empty headsets (no transducers), magnetic elements, and electrostatic elements. Hmmm ... Later this year I'll be hanging around with 30-50 experimental psychologists. If I remember this thread, I'll ask around.

  11. davenn

    davenn Moderator

    Sep 5, 2009

    extremely tiny ones ..... would be giving him the results he's seeing
  12. davenn

    davenn Moderator

    Sep 5, 2009

    which is stupid, as the Earth's magnetic field strength at the Earth's surface ranges from 25 to 65 microteslas (uT)

    The typical paranoia we see here from time to time
    and with that and all the good answers

    Thread closed
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