How the coil of a contactor works

A demonstration of how back emf works with the iron core of a contactor coil
This video is part of the heating and cooling series of training videos made to accompany my websites: and to pass on what I have learned in many years of service and repair. If you have suggestions or comments they are welcome.
If you are a homeowner looking to repair your own appliance, understand that the voltages can be lethal, the fuels are highly flammable and high pressures are used. Know your limits.

15 Replies to “How the coil of a contactor works”

  1. Thank you very much Mr. Grayfurnaceman, I learned a lot from all your videos. You just did know how much I appreciate it.Thank you more power and God bless you.

  2. Excellent video
    I am always facing problem with AC contectors central units . They get burnt and compressor shutdown . Before I always keep spare contactor for replacement . I decided to try rewinding the coil and find that great success. The rewinded coils stays three times loger than origenal.

  3. Another excellent video. Do you know how PSC motor manufacturers determine what size capacitor to use with their motors? I suppose that I could google it but I thought that it might make an interesting video.

  4. using ohm law is possible then to have a diagnostic in relay, contactor and coils? with the inf label

  5. this video is amazing, but i hope you will explain about Medium voltage contactor, because there are some coil like closing coil, open coil, holding coil, how those things work sir(the principle)? because my lecturer said the different between low voltage contactor and middle voltage contactor is from the coil beside the voltage, can you explain it or link me to the web that will explain it or you have the video about that???

  6. Would it be more difficult to detect a back emf problem on a 3 phase contactor versus a single phase?

  7. Thank you for a very informative video.
    If I may ask you for your opinion, I have a size 3 magnetic starter with 110 v coil. The 110 v is going through a fuse then to the OFF swt then the ON swt with auxiliary contact across it. When the ON swt is depressed the fuse blows. Specs says 4.1 amp draw for the coil. I'm using 10 amps fuse still blowing. This circuit is being used for a 30 hp rotary phase converter.

    Thanks for your feedback

  8. You are the real deal sir straight to the point with no fancy shit words like the other guys on YouTube channels and that's more understandable point of view thank you

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