Size disconnect for transformer

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coop3339

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Do disconnects have a make rating? I have a situation where a manufacturer of a 1600A fusible disconnect is saying that the inrush of a 500kva transformer exceeds their switch rating. The disconnect is operating a Gnd-Wye/Gnd-Wye 500kva transformer. The transformer is being used to step up from 120/208 to 277/480. The disconnect is a bolted pressure switch on the 208 side. After operating a few times to power off and on the transformer the center phase contact welded closed. There was no load on the transformer during switching. Also the fuses didn't blow in the disconnect. We were finally able to get it to open after applying manual pressure on the disconnect handle while tripping it. There is now obvious signs of arcing on the middle phase and visible soot. The manufacturer is refusing to replace the disconnect. Any help would be greatly appreciated.
 
The disconnect is load break rated and is a service disconnect. It supplies the 500kva transformer and is fed from a lineside tap ahead of the existing services main.
 
Why would you want to open the disconnect under load? I'm not being arguementative. I just don't understand why you would need to cycle the disconnect while the tranny is loaded...
 
One brand says their bolted pressure switches are suitable for making 6x rated current and breaking 12x rated current. The short time inrush of the transformer could very easily exceed 6X the switch rating. This short term inrush, or magnetizing current, does not really change if there is a load connected to the transformer or not.
 
That's interesting, I'm surprised the make rating is smaller than the break.

The one we have does not include a make or break value. All I can find is it says load break so I assumed the break rating to be 1600A, the same as the disconnect.

I was thinking that the 'make' would be equal to or greater than the highest fuse available of the type specified, in this case 'L' class, under 1600A of course.
 
If I may ask, is this either a step-up transformer, or a step-down approved to be used as a step-up?
 
coop3339 said:
That's interesting, I'm surprised the make rating is smaller than the break.

The one we have does not include a make or break value. All I can find is it says load break so I assumed the break rating to be 1600A, the same as the disconnect.

I was thinking that the 'make' would be equal to or greater than the highest fuse available of the type specified, in this case 'L' class, under 1600A of course.
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Yes, most often it is the other way around for any type of inductive load.
 
Approved to be used as Step-up probably but I'm not sure. You thinking a trans made for step-up may have a lower inrush? I didn't think about that. I'll have to see if I can find a cut sheet
 
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