A situation accured that tripped a 20 amp breaker. The breaker feeds a 120v, 1/2 HP motor with a capacitor. Its FLA is 10 amps. It runs a shop roll up door. When the door goes down it runs at about 9.5 amps. When it goes up it runs about 40 amps. I changed out the cap and it still does it. it theory the only way it can pull 40 amps is because the resistance now it too low. Is this true? If so then I would think that maybe it is because the is a break down in the insulation on the windings thus creating a lower resistance in the circuit. Why wouldn't it go to 40 amps going down though?
Single Phase 120 volt cap start motor.
- Thread starter JdoubleU
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Lifting the door is the only part that requires hp, in principle. A 1/2 hp (280 ft-lbs per second) motor should be able to lift a 280 lb door one foot in one second.
If the motor has lasted it's because this 40A load is only temporary.
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- Licensed Electrician
Until a motor starts turning it is, in essence, a short circuit. Until it comes to full speed it will pull more amps because of too much slip.
Your not pulling 40A going down because gravity helping.
Bent pulley or some worn bearings might be the cause.
Actually, on second thought, the door should be counterbalanced by weights or "negator" springs so the motor is only used to overcome friction, like in an elevator.
Using a stiff spring in series with a comealong you can measure the force required to lift the door. You measure the elongation of the spring - for storm door snubber springs it's about 40 lbs per inch.
Using a stiff spring in series with a comealong you can measure the force required to lift the door. You measure the elongation of the spring - for storm door snubber springs it's about 40 lbs per inch.
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- Licensed Electrician
Your right about the springs. There is still something wrong with the door or the motor and it is not the insulation.
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