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Setting overload Amps for motor starter

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  • Setting overload Amps for motor starter

    I have an overload protector with variable setting on the motor starter for my drill press. The motor is 2-speed, 220V, 3~. Amps listed for each speed are 2.35A and 2.5A. Also powered through this same starter is:

    *240V-120V transformer, McMaster #6988k31
    *From the 120V control line...
    -pole-changing reversing switch
    -25 watt light, McMaster #1611k29

    It is all for the same machine in my previous "electrical" threads if you need more information: HSM Thread 1, HSM Thread 2

    My question is.. what is the standard practice for setting an overload amp level? For example, should I add a standard percentage to the motor's listing of 2.5A? How many more amps might the secondary components listed above add to the amperage draw?
    Last edited by Arthur.Marks; 10-04-2010, 12:12 AM.

  • #2
    You should segregate the auxiliary loads from the motor load. The amp draw of these auxiliary loads would be a significant percentage of your full load motor amps, the light being particularly troublesome as it can be turned off/on or burnt out.

    Or you could just set the overload at something like 2 amps and then use the machine until it trips and then gauge what you were doing at the time to see if or how much you should adjust. It won't be like you are having to buy a box full of heaters.

    Dave

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    • #3
      between 1.10 and 1.25% of motor FLA

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      • #4
        Originally posted by JoeFin
        between 1.10 and 1.25% of motor FLA
        Yep.... refer to latest US electrical code under "motor controls".
        1601

        Keep eye on ball.
        Hashim Khan

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        • #5
          Has anyone thought to look at the heater current listing for a motor switch? Example:-on the inside cover of a GE motor switch is a listing of the current capacity of the heater required for each listed motor HP from about 1/8HP up to about 2HP. There is a similar table in AB and SquareD switches.
          Duffy, Gatineau, Quebec

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          • #6
            Originally posted by becksmachine
            You should segregate the auxiliary loads from the motor load. The amp draw of these auxiliary loads would be a significant percentage of your full load motor amps, the light being particularly troublesome as it can be turned off/on or burnt out.
            That thought occurred to me the minute I wrote out the question last night Unfortunately, it will be a major PIA to separate them at this point... I may just leave it as is for now, and delegate that task to another day. The reason I asked is because I didn't adjust the overload setting when I originally installed it. The switch tripped yesterday, and it had been on 2.4A. So I bumped it up to 2.8A and was just wondering what "correct" procedure is.

            WRT the auxiliary equipment, using the equation Watts/Fixed Voltage=Amps, the lamp is not a large percentage of the amp draw at .2 amps. That is about 8% of the FLA as listed on the motor---far less than the +25% mentioned in the above responses. The reversing switch control... who knows? I doubt it is more than the lamp, even.

            I think I'll bump the overload setting up to 3A and let it be. Thanks for the responses, I appreciate it.
            Last edited by Arthur.Marks; 10-04-2010, 10:44 AM.

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            • #7
              Most motor data plates have a SF usually with something like 1.15 stamped on them, this would indicate that your O/L protection be set at 15% above the motors FLA, metering the motor might be a good idea while it's doing some useful work as these numbers can be different depending on said individual equipment. As it tripped you likely did exceed the setting but O/L's can become weaker overtime especially ones that have tripped often in the past. We usually go by 10% over as a quick general rule......and if 3 phase check that the phases are close to one another.

              That said I'm not sure 2-3 amps is worth the effort and would be inclined to increase the setting and carry on as you've done.......
              Last edited by hardtail; 10-04-2010, 10:54 AM.
              Opportunity knocks once, temptation leans on the doorbell.....

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