fuses are blowing during mains failure

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Thread Starter

pradeep dalvi

we installed hoist drive in crane in port trust
when crane is lowering and mains fail, we found semi fuses are blowing many times

what could be the solution ?
 
W

William Hinton

If the crane is powered by DC, when lowering the hoist brake is released and the dynamic braking circuit puts a heavy DC load across the armature during lowering as well as a load-brake (band brake with lining) in the gear box housing. Those are the most likely places to look.

If the crane is powered by AC when lowering the hoist brake is released and the load-brake helps control the speed during lowering with a heavy load. The hoist brake and load-brake are likely places to look but the other issue is:

What is the class of the hoist motor? Most of them are class 30 and need to fused higher than standard class 10 or class 20 motors. The NEC indicated fuse size at 175% of the motor FLA but the class 30 motors in your intermittent duty application may allow fuses rated for 210% of the motor FLA.

Also AC electric motors need properly sized dual-element time delay fuses like FUSETRONS.

I hope this helps,
William Hinton
 
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