Question about Square D Ehb24020pl 20 A Ehb4 Ehb Circuit Breaker

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High amp start up draw

I have a Craftsman 2.5hp radial arm saw. When trying to use it on a 15amp circuit (as the manual says) it doesn't come up the full speed and trips the circuit after running about 20 seconds. In checking the draw on the line I found the motor pulling 39 amps on start up and I show 123+ volts on the line. If I plug into a 20 amp circuit it comes up to full speed in about 5 seconds drawing 39 amps then dropping to 9 amps when reaching full speed, line is showing 125 volts Thoughts as to why?

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6kw what!!!! more like 1.08kw the saw is fine

Posted on Oct 08, 2009

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All electric motors require additional power to get the rotor up to normal operating speed. The amount of current that is required depends on the starting load, in this case the weight and inertia of the blade itself and the moving parts of the motor. Motors that have very high starting loads, like a shop compressor for example, usually have one to three capacitors mounted to the motor to provide the additional starting power. If the owners manual specifies a 15 amp circuit and the saw doesn't work, I would check to see what else is on that particular circuit. If there are no other loads on the circuit and it still trips, you need to have the saw motor checked before it burns out.

Posted on Feb 26, 2009

  • Fahr Quad Mar 13, 2009

    So did you have to get the brushes in the motor replaced???

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I don't care what kind of stories Craftsman tells, their numbers don't add up.
One horsepower is ~ = 740 watts of energy.
2.5 hp equates to a steady-state power consumption of  ~1850W and this could be 50% higher during the first second or two after turn-on.  Your 15 Amp circuit is pushed to the limit by that power level; 15 Amps X 120 VAC = 1800W And, motors aren't a breakeven game; part of the power they draw is wasted in heat.

9 amps steady-state would be a power consumption of over 6kw which cannot be right. Either your measurements or the motor is faulty. 







Posted on Dec 15, 2008

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