I am checking a 15HP 3 phase 480v motor. With all the leads connected I read a direct short to ground on 1, 2, and 3. I disconnected all the leads in the motor, and now I read nothing to gound on leads 1,2,3,4,5, and 6. I read a direct short on leads 7,8, and 9. The motor will run on manual but will not run on the speed drive. Have you ever heard of a motor running when three leads show a direct short to ground. Any help would be appreciated.
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Another 3-phase motor question
- Thread starter Zigman111
- Start date
- Joined
- Jun 22, 2002
- Messages
- 934
It is very hard to diagnose a problem without the motor being in front of me. However a three phase motor should have 6 lead which connect to the motor coils one coil per phase. These 6 leads are normally coneted in a star configuration with all the a ends connected together but insullated from anything else with one phase connected to each of the b ends of the coils.
The other way is connected in a delta pattern each coil connected b end to a end of the next coil with one phase connected each ab connection.
I don't know what the extra wire are from. It has been 20 years since I worked as an electrician so good luck.
The other way is connected in a delta pattern each coil connected b end to a end of the next coil with one phase connected each ab connection.
I don't know what the extra wire are from. It has been 20 years since I worked as an electrician so good luck.
- Joined
- Mar 18, 2007
- Messages
- 5
Leads 1,2 & 3 are the "A" side of coils 1, 2 & 3. Leads 7,8 & 9 are the "A" side of coils 4,5 & 6 . 4,5 & 6 are the "B" side of of coils 1,2 & 3. The "B" side of coils 4,5 & 6 are tied together inside the motor. Any short to ground on any of the second set of windings will show up on leads 7,8 & 9. How are you checking & what are your readings.
- Joined
- Mar 18, 2007
- Messages
- 5
By the way, a 9 lead motor ( one that's NOT shorted ) can be wired for either 240/208 or 480.
Triphammer is right...this is a dual voltage motor.
The proper 480 volt wire up would be line to leads 1, 2, and 3.
Leads 4 & 7 tie together
Leads 5 & 8 tie together
Leads 6 & 9 tie together
To wire for 230 volt:
Line leads would be:
Leads 1 & 7---line
Leads 2 & 8---line
Leads 3 & 9---line
leads 4, 5 & 6 tie together
To check for a grounded motor take an ohm reading (preferably with a megger---but a VOM on it's highest scale may work) and take a reading from each indivual line lead to ground (metal frame of motor). The meter should (idealy) read infinity. If you get a low reading here, ther motor is grounded and needs to be re-wound.
Next read between the line leads of the motor with the meter on R x 1 , or lowest scale (1 to 2, 1 to 3, 2 to 3 on 480 volt---1 & 7 to 2 & 8,1 & 7 to 3 & 9, 2 & 8 to 3 & 9 on 230 volt tie). This reading is checking the continuity of the windings and should be very low ohms (near zero) and all windings must read the same. If the readings vary from one set of line leads to the next or one should read open then the windgs are damaged and the motor needs to be re-wound.
Hope this helps.
-Mike-
The proper 480 volt wire up would be line to leads 1, 2, and 3.
Leads 4 & 7 tie together
Leads 5 & 8 tie together
Leads 6 & 9 tie together
To wire for 230 volt:
Line leads would be:
Leads 1 & 7---line
Leads 2 & 8---line
Leads 3 & 9---line
leads 4, 5 & 6 tie together
To check for a grounded motor take an ohm reading (preferably with a megger---but a VOM on it's highest scale may work) and take a reading from each indivual line lead to ground (metal frame of motor). The meter should (idealy) read infinity. If you get a low reading here, ther motor is grounded and needs to be re-wound.
Next read between the line leads of the motor with the meter on R x 1 , or lowest scale (1 to 2, 1 to 3, 2 to 3 on 480 volt---1 & 7 to 2 & 8,1 & 7 to 3 & 9, 2 & 8 to 3 & 9 on 230 volt tie). This reading is checking the continuity of the windings and should be very low ohms (near zero) and all windings must read the same. If the readings vary from one set of line leads to the next or one should read open then the windgs are damaged and the motor needs to be re-wound.
Hope this helps.
-Mike-