1" lb

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mickeyrench

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edison, n.j.
I just found some 1" lbs and 1" gal. conduit with 3 # 3 and 1#8 for a 50 hp 480v motor. Motor burned up. Do you think the undersizing of the lb and conduit had anything to cause the early demize of the motor?
 
could have....between the electrons being squeezed and not being able to make that sharp turn in the LB. Did you see any tracks from wayward electrons ?
 
mickeyrench said:
I just found some 1" lbs and 1" gal. conduit with 3 # 3 and 1#8 for a 50 hp 480v motor. Motor burned up. Do you think the undersizing of the lb and conduit had anything to cause the early demize of the motor?
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I don't ... but then I'm not the sharpest knife in the drawer either.

Do you think there was heat not dissipated that caused a problem, or what?
 
realolman said:
I don't ... but then I'm not the sharpest knife in the drawer either.

Do you think there was heat not dissipated that caused a problem, or what?
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A SWAG would be that the conductors heated up causing resistance which in turn reduced the voltage to the motor and due to excess rotor slip the motor overheated and met an early demise.

SWAG = Scientific Wild Arse Guess
 
Back to the OP
There is just too much we do not know other than the size of the LB/Conduit.
I have seen too many installations where this is so and the equipment is still operating, so I would think more investigation is necessary.
 
How long is the circuit run? Are the conductors copper or al? What type of insulation are the conductors? Full load of a 50 hp motor at 480v is aprox 65 amperes and a #3 cu at 60 c is rated at 85 amperes hard to imagine that the overfilled lb would cause the burn out.
 
Unless the conductors were damaged when they were installed, I don't how the conduit or LB size would have any effect on the motor.
 
If the wire is THWN then these conductors fit in a 1" conduit (except PVC 80 or FMC).

I'm sure we all agree a normal LB won't be labled for that though.

But if they got them installed with no damage to the insulation, should be ok.
 
Volta said:
But if they got them installed with no damage to the insulation, should be ok.
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I dunno, you'd have to really jam that last conductor loop into the LB... I've definitely had to do some fixes of conductors mangled by undersized conduit bodies.

Admittedly, I was the mangler at one point.
 
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