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wiring 240 volt magnetic starter for compressor

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  • #16
    Went to a real tool house today and was told that my mag starter isn't that, but just a manual still need a mag starter. They also said the head has the ability to run all the time, by some style pressure unloader built into those older heads. He also said that the easiest to do is get a check valve from the tank to the pressure switch, as there is none from the pics I posted, which I brought to the tool house. He figures the engine pulley is much to large for a 5hp...he figures 7.5 hp needed or bigger but it would run fine with 5hp and drop pump rpm to near 400. I told him about the 600-900 rating on pump but he said it is a splash type oil system head and would still be ok. He figured the head was working under pressure when starting as the pics didn't show any check valve.

    So I need a mag starter again. They had, but I'll try to find one used perhaps to keep my costs down.

    He offered to buy it a couple times
    Nah , Ill keep it.
    He said its an expensive head to rebuild.


    • #17
      Finally hooked it all up.

      Well I finally got it all together. I moved last month and had the garage to hook it all up in finally. I did find a magnetic starter at a yard sale of all places for $20 and upped the heater to 30 amp rating for the magnetic starter for another $20. The definite purpose switch I had a 33 amp heater in and put it before the mag as I had it anyway and gives me a shut off near the compressor. I ran about 35 feet of 8-2 wiring ($50) from the panel and used a 40 amp breaker there. So it smoke to let out. I ran pressure switch wiring to points on the starter to activate the throws of the mag. The pressure switch is not doing activation of the motor as the mag switch does that task. Should save the duration life of the pressure switch that way.
      Pics attached of the final final.
      Attached Files


      • #18
        Good to hear a 3 hp might not do. This one dims the lights withs its 5hp as it starts but its good to go IMHO. Knuk


        • #19
          I would clamp a Amprobe on a lead and run the compressor up to the maximum perssure your pressure swith is set at and take a reading.
          Lower than the 26 amps your good to go, higher your overloading the motor
          and should down size the motor pulley until the amperage is at or lower than 26.
          Sorry i'm late finding this thread, got my attention when I saw that manual switch/overload protection you had, not a mag starter.
          Maximum locked rotor current is 6 times rated load current. Disconnecting means (your manual switch) shall be rated 115% of the full load current.
          For your 5 hp motor that requires a NEMA 1 starter.


          • #20
            You do not need 2 starters for your compressor (the manual Furnas starter does NOT qualify as a disconnect switch) a cheap 60 amp A/C pullout disco works well, and that exposed wiring is scary, conduit and proper grounding/bonding of all parts is required for the safety of you and others.