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Trouble shooting three phase motor- where to start.

Trboatworks

Diamond
Joined
Oct 23, 2010
Location
Maryland- USA
I have a five hp three phase motor on a machine which won’t run.
It surges briefly- like a 1/8 turn when I connect to power and makes a deep hum but won’t run.

Where to start troubleshooting?

The motor is spins perfectly free.

Thanks all
 
Step one.... make sure all wires are carrying current. If not , proceed. If so, then there is another issue, possibly with the connection of coils.

Step 2 make sure all 3 are properly connected

Step 3 check resistance of all 3.
 
Ok- I checked supply- all is good.
This is a large belt sander and the 5 hp is the primary belt motor.

The machine also has a three phase oscillating motor which works fine.
 
You guys were right on it and that helped sort it out- the service disconnect for the main motor had punky contacts and were dropping a leg.

Thanks
 
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