Corner grounded 3 phase motor install tripper breakers and blowing fuses

Status
Not open for further replies.
B

Brad7981

Member
Location
Warsaw
Occupation
Maintenance tech
Hello,

I am working on a motor install for a corner grounded (480 grounded b phase system).

Motor - 50 HP Leeson wired for 480. Motor shaft spins freely by hand. Motor passed all the multimeter test prior to wiring.

breaker - 350 amp siemens (existing is the only reason its being used) with all three phases turned to 1 (8 is the highest setting).

When we tried to start it it made a buzz and then popped a a slow blow fuse in the disconnect on the grounded b phase. The 350 amp breaker also tripped (all three phases turned to one).
My question is could this problem all be related to the breaker phase settings being turned to one?
 
Double check the phasing of the motor connection.

With a multi voltage motor you can mis-connect such that you have two competing rotating fields, or the portions of an individual winding could cancel each other out.

Jon
 
Brad7981 said:
Hello,

I am working on a motor install for a corner grounded (480 grounded b phase system).

Motor - 50 HP Leeson wired for 480. Motor shaft spins freely by hand. Motor passed all the multimeter test prior to wiring.

breaker - 350 amp siemens (existing is the only reason its being used) with all three phases turned to 1 (8 is the highest setting).

When we tried to start it it made a buzz and then popped a a slow blow fuse in the disconnect on the grounded b phase. The 350 amp breaker also tripped (all three phases turned to one).
My question is could this problem all be related to the breaker phase settings being turned to one?
Click to expand...
If only the breaker opened, I might say yes, but would need to know a lot more about the breaker to really say.
Assuming the fuse is correctly sized, the fuse blowing indicates a problem with the motor itself or some issue with the mechanical load that the motor is driving.
Note that unless the fuse is being used as the motor overload protection, you are not permitted to have a fuse in the grounded phase, See 240.22.
 
don_resqcapt19 said:
If only the breaker opened, I might say yes, but would need to know a lot more about the breaker to really say.
Assuming the fuse is correctly sized, the fuse blowing indicates a problem with the motor itself or some issue with the mechanical load that the motor is driving.
Note that unless the fuse is being used as the motor overload protection, you are not permitted to have a fuse in the grounded phase, See 240.22.
Click to expand...
This is when the dummy fuse could come into play. And when you use it or do not use it.
 
Something else you may want to add is how this motor is started.
What type of controller etc.
Across the line
Soft start
Vfd etc.

Disconnect with blown fuse location in regurards to the controller.
 
What size and type/class fuse? The 50 hp 460 motors I wired used busman 80 amp time delay, centrifugal water pumps
 
You didn’t specify the breaker model, but usually if it has just one dial (or one one each phase) it is a magnetic trip adjustment, not amperage. But if it’s blowing a fuse too, it’s most likely a motor issue as others have said. You said you checked with an ohmeter, so I am assuming you checked each lead to ground. A fault to ground from one of the other two phases would also blow a fuse.
 
Status
Not open for further replies.
Top