Magetic contactor humming noise

  1. Hello.
    The ac contactor with two magnets sometimes give a noise.For some contactors humming is more audible.What are the possible causes of humming.
    Also what is the effect of humming on performance of contactor.Can anybody help on this subject?
  2. jcsd
  3. berkeman

    Staff: Mentor

    What's an AC contactor? How is it constructed, and what voltages and currents are involved?

    There are two main sources of audible noise from AC voltages. The first is magnetostriction, when the AC voltage is placed across a coil around a magnetic material. The AC magnetic field that is induced in the magnetic material causes physical deformation at the excitation frequency, and this physical deformation can generate an audible noise. That's the main reason that big AC transformers hum at 50/60 Hz, and why you sometimes can hear a 15.750kHz squeal from the flyback transformers in TVs (that's the US frequecy).

    The other cause of audible noise from 50/60 Hz voltages is around high-voltage power lines or switching yards, where you can get some corona discharge from the HV lines when the air gets humid enough.

    So if the AC voltage is across a coil with magnetic material, the cause is magnetostriction. If the AC voltage is HV and there is no magnetic material involved, it is likely corona discharge.
  4. dlgoff

    dlgoff 3,158
    Science Advisor
    Gold Member
    2014 Award


    AC contactors are a common name that electricians use. They are heavy coil and contact relays; used for such thing as switching on three phase motors.


    Probably most of what you are hearing is due to vibrations of the contactors housing/enclosure. The force of the coil to contact causes the 50/60 Hz hum which is transmitted through the enclosure.
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