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mag starter

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  • mag starter

    Can anyone explain how a magnetic starter works? I have one that someone took the terminals off ?? How do i tell which is which?? L1-L2-L3-T1-T2-T3???? Thanks Greg

  • #2
    Hmmm...let's see...basically, there's a coil that when energized pulls the contacts into the closed position. The coil is energized usually by one of the incoming hot leads such that it latches the contacts closed. Loss of incoming power will de-energize the coil shutting off the machine. This is a nice safety feature, like in the event of a power outage the machine will not start when power is restored.

    Can't you trace the terminals through the contacts?


    • #3
      I probably could but --i am an electrical idiot!!


      • #4
        Normally L1 (line 1) corresponds to T1 (trip or load 1)

        There may be timing heaters depending on the type of starter. (adding confusion - and I don't remember what they are for either I am not an electrician)

        There should also be terminals for the pull down coil, or they may be mounted on the coil itself.


        • #5
          L1,L2,L3 refer to the power lines coming into the starter contacts on the same side as the coil, while T1,T2,T3 refer to the lines out going to the motor leads on the opposite side.The other thing you need to know about your starter is the coil voltage,they come usually in 12,24 110,220 and440vac.You need to determine which one you have before you can go any further.
          I just need one more tool,just one!


          • #6
            If you have the complete starter, somewhere in the housing there should be a schematic and wiring diagram.

            Besides the what was mentioned above, you also need to have the correct overload protection heaters installed or if its a newer one you have to adjust the overload.

            There is usually a chart in the housing giving the proper heaters for a specific amperage range. The amperage will be found on the nameplate of the motor. Generally mag starters are used on 3 phase equipment, but there are single phase units out there too.
            Yours is 3 phase (L1,L2,L3=line 1,2,3)
            The coil is usually marked somwhere with its rated voltage and they are sometimes replaceable with different voltage coils available.

            It will help you to understand how it works if you remove the actual contactor and overload unit out of the housing. There are usually 2 to 6 screws holding it in. They are made easy to remove, for wiring purposes and for replacing components. Usually the contactor is a separate unit from the overload, connected by wire or stamped metal jumpers. The contactor is basically a set of contacts brought together by an electromagnet. You will probably be able to see the coil and 2 tabs or terminals or wires comeing out of it. Many contactors can be opened, for inspecting or replacing burned contacts. It may have a quick opening cam or latch or several screws in the top face. If you can see the workings of it, you can trace the path from say, L1 through its contact into the overload and through to T1.
            There are only overloads on 2 of 3 phases.
            The coil terminals when supplied with current pull in the contactor, which will then close the contacts. There is an additional set of contacts that then maintains the power to the coil after you let go of the start button, that will be interupted when you push the stop button.
            Current then flows from L1,2,3 through to T1,2,3, and starts your motor.

            I think I've been droning on too long

            If after reading this and carefully looking at the thing you still feel intimidated, then for safety's sake get a friend who is familiar with it or an electrician to explain it to you and also hook it up.


            • #7
              Yuo havegood info all the way!. That last sentence by YF has aworld of wisdom!

              You may be confused by seeing four terminals and four sets of contacts. that fourth set is for , as explained by others" the "holding contacts". You push button controler (on &stop) is also confusing. the on contact is a momenarty closed switch. The stop button is always "on" unless pushed then it opens and breaks the path the the coil. The protective devices slip into a coil of wire that heats depending on the current flowing. They must be chosen, as said before, the match the name plate of the motor. Too small a device and you get un-needed tripping, too large is like putting pennies behind as fuse. (only old codgers know about that stunt- right )