[hdgeno777]

I have three identical exhaust fans on a job, two of them work, but the third instantly tips the breaker in the starter cabinet when I try to turn it on. If I disconnect the wire to the motor the circuit is fine so I know it's in the motor.

Both capacitors are good after checking with my meter, no impedance when spinning the fan by hand, winding is not shorted to ground, 0.8 ohms when I read the winding. What am I missing that is causing the breaker to trip? Thanks in advance for any help

 

[Vintage Sounds]

It might be time for a megger test, if you have one available.

 

[AllWIRES]

It might be time for a megger test, if you have one available.

About that time.

 

[ponyboy]

It might be time for a megger test, if you have one available.

I'd tend to agree but I find it odd that it dead short so consistently yet a standard dmm doesn't reveal it

 

[hdgeno777]

I don't have a megger at the site, but should be able to get my hands on one in the morning. I'm quite inexperienced troubleshooting motors (obviously), and haven't used a megger much in my career. I'm thinking there's got to be a problem my meter can't pick up, since the info I have indicates the motor is good

 

[hdgeno777]

What would happen if the caps were installed backwards (start and run flipped around)?

 

[bkmichael65]

I have three identical exhaust fans on a job, two of them work, but the third instantly tips the breaker in the starter cabinet when I try to turn it on. If I disconnect the wire to the motor the circuit is fine so I know it's in the motor.

Both capacitors are good after checking with my meter, no impedance when spinning the fan by hand, winding is not shorted to ground, 0.8 ohms when I read the winding. What am I missing that is causing the breaker to trip? Thanks in advance for any help

Do you have run, start and common terminals? Where are you reading .8 ohms at? The windings should have a higher resistance than that

 

[dmxtothemax]

Shorted turns rather than a short to frame would cause a lower than
normal reading, but not indicate a dead short on a ohm meter.
if this is the case it is history !

What is the resistance readings of the other exhaust fans ?
Are they the same make and model ?
If so compare them.