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Old 08-27-2010, 05:03 PM   #1
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I have a 230V 7 HP motor with a 30Amp fuse. Pops the fuse every 2-3 days. How can i test the amp draw on the motor?? Its not making any sounds. Its a Franklin unit with twin capacitors 2 speed

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Old 08-27-2010, 05:10 PM   #2
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Is the motor single-phase or three phase? A 7.5 horsepower single-phase motor draws 40 amps @ 230 volts. What is the nameplate rating on the motor?

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Old 08-27-2010, 06:13 PM   #3
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Twin capacitors indicate this is a single phase motor. 3 phase motors do not need capacitors to start/run.

30 Amps is way too little overcurrent protection to properly operate any motor over 3 hp.


I believe that the 7 hp is a fantom rating, and the actual motor is much smaller than that.

Care to post a close-up of the nameplate of the offending motor??
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Old 08-27-2010, 06:56 PM   #4
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Originally Posted by kbsparky View Post
I believe that the 7 hp is a fantom rating, and the actual motor is much smaller than that.
I agree. The 7HP is probably the operating horsepower equivalent of the locked-rotor amps. I guess the motor's actual nameplate HP is no more than 3.
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Old 08-28-2010, 09:42 AM   #5
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Originally Posted by jrf0022 View Post
I have a 230V 7 HP motor with a 30Amp fuse. Pops the fuse every 2-3 days. How can i test the amp draw on the motor?? Its not making any sounds. Its a Franklin unit with twin capacitors 2 speed
If this where a true 7 Hp motor (It's not, they don't build 7 HP motors standard) you could use a 100 amp breaker for this motor. NEC Article 430.52.
I used 7.5 HP for the calculation as that is the closest NEMA size listed in the NEC.

You should look at the instructions and see what the manufacturer recommends for the breaker (OCPD) size. Call them if you must.
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Old 08-29-2010, 03:59 AM   #6
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There one thing with single phase motours is the starting switch I know few of them will get sticky and can cause the breaker to trip ditto with bad capaitors as well.

To OP you should check the control panel to make sure the relay is working properly to prevent both low and high speed running at the same time unless the motor nameplate do require it{ I doubt it good chance to trip the breaker or blow the fuse no question asked }

That " so called 7 HP " motor the real current dawage will be much lower than the real deal 7.5 HP motor { of course it will be much larger as well }

The so called 7 HP motor the current drawage should be anywhere from 15 to 22 amp IIRC but verify with nameplate info it will stated AMPS there will be a number next to it that will tell ya what the actaual current drawage.

To read the amp drawage you will need to use the clamp on ampmeter DO NOT use the DVM at all { it will destory pretty fast from current surge }

If reading too high you have to check it out why as I mention starting swtich or few others issue may come up. { some case bad connection can do this way as well }

Merci.
Marc

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