amp on motor

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electricalist

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dallas tx
yesterday we were checking ex fans in a large warehouse 40 ft to the deck where the fans are.
480 v 3 phase 20 amp breaker feeding each .
switch to starter, to motor...turned each on,,,nothing,,,amp probe says about 6 after in rush.
If the belts are off the fans will that affect amps?
 

GoldDigger

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Placerville, CA, USA
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yesterday we were checking ex fans in a large warehouse 40 ft to the deck where the fans are.
480 v 3 phase 20 amp breaker feeding each .
switch to starter, to motor...turned each on,,,nothing,,,amp probe says about 6 after in rush.
If the belts are off the fans will that affect amps?
If the air flow path of moving fans is blocked, that will also affect the amps, although not as much.
 

electricalist

Senior Member
Location
dallas tx
From the ground i cant tell if the motor is turning.
We are there to see if motors work, can work, cant work etc. Of the 18 only these 3 didnt work so we will bring our lift out.
Any tips on checking a motor from the ground? We turned 3 on 2 were pulling amps 1 was not. visually none were working
 

GoldDigger

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Location
Placerville, CA, USA
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Retired PV System Designer
From the ground i cant tell if the motor is turning.
We are there to see if motors work, can work, cant work etc. Of the 18 only these 3 didnt work so we will bring our lift out.
Any tips on checking a motor from the ground? We turned 3 on 2 were pulling amps 1 was not. visually none were working
Short note: in addition to missing belt it could be a broken or missing shaft key.
 

ActionDave

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Durango, CO, 10 h 20 min from the winged horses.
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From the ground i cant tell if the motor is turning.
We are there to see if motors work, can work, cant work etc. Of the 18 only these 3 didnt work so we will bring our lift out.
Any tips on checking a motor from the ground? We turned 3 on 2 were pulling amps 1 was not. visually none were working
The one that's not pulling any amps is for sure not working.
 

augie47

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Tennessee
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State Electrical Inspector (Retired)
The one that's not pulling any amps is for sure not working.

That pretty much sums it up.
If it's pulling normal or less amps it's running.
If it's on line and unable to turn it will pull incredible amps for a short while.
Keep in mind some exhaust fans come with a local disconnecting means. If you didn't connect them and haven't gained full access if one is not running the local disconnect may be off,.
 

electricalist

Senior Member
Location
dallas tx
I was thinking it probably has a 3 pole switch or disconnect at the motor and either ill go on the roof or when our lift is there see for sure.
I also am curious if 2 motors are on 1 breaker would i be able to think the amps that are higher is the farthest motor. Or are there too many reasons that could happen.
Also these motors have starters. The have a normal coil feed and a bypass feed. If they didnt need the bypass feed would they still need a starter. I have seen similar motors that were just on a breaker. Also one of these had a contactor where one of the starters use to be.
 

augie47

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Tennessee
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State Electrical Inspector (Retired)
I was thinking it probably has a 3 pole switch or disconnect at the motor and either ill go on the roof or when our lift is there see for sure. .
:thumbsup:
I also am curious if 2 motors are on 1 breaker would i be able to think the amps that are higher is the farthest motor. Or are there too many reasons that could happen..

Reasonable distance should not effect amps to any noticeable degree.
Also these motors have starters. The have a normal coil feed and a bypass feed..
o.k.
If they didnt need the bypass feed would they still need a starter. I have seen similar motors that were just on a breaker. Also one of these had a contactor where one of the starters use to be.
Motors need overload protection per Art 430 Part III. Unless the motor has built in overload protection which, in my experience is rare on 3 phase motors, the starter in addition to a means of control provides overload protection. Contactors do not provide overload protection.
 

augie47

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Location
Tennessee
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State Electrical Inspector (Retired)
Overload protection is for the motor where a breaker is for the circuit?
Somewhat !:)
The circuit and the motor are protected against short-cirtcuit/ground-fault and overload.
Most often by separate devices, one for overload such as a starter, with a fuse or breaker providing SCGF protection.
That's a very simplistic answer and there are many variables.
 
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