Fuse Size

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Alwayslearningelec

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NJ
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Asking me to run temp power to hoist. They are using the standard hoist on the cut sheet that's a 150A FLA.
They are saying there's a 100A existing spare fused switch and want to know if we can put 150A fuses in it and that would work.
I see the label on the switch says 100A so I'd assume that's the limit and would not work in this situation.
It's not like it's a 200A with 100A fuses where there would be more available current to provide.

Correct? Thank you
 

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imho, If the switch is labeled 100 Amps, then 100 amps is the largest fuse size the switch can accommodate.
 
THanks. I think that's a "bucket"/fused switch inside a switchboard. Could we change out the switch to a higher rated?
But then we would have to make sure the distribution board could handle the increased load, correct?

How would one go about that? Demand metering?
 
You would also need to assure the conductors were sized properly.
 
don_resqcapt19 said:
The physical size of fuses changes as the current rating changes. 0-30A is one size, 31-60 is another, 61-100 is a size, 101-200 is a size, 201 to 400 is a size.
Click to expand...
Understood. Then 150a fuses would fit in 100A holder? That's one thing. Another is the board being able to handle the increased load, correct?
 
horsegoer said:
Understood. Then 150a fuses would fit in 100A holder? That's one thing. Another is the board being able to handle the increased load, correct?
Click to expand...
No, the maximum size in a 100 amp fuse holder is 100 amps. A 150A fuse will only fit in a 200 amp fuse holder.
 
They make reducers to put smaller frame sizes into larger fuse holders but not the other way around. Even 110 amp fuses are physically too big to fit a 100 amp fuse holder. They are same physical size as 200 amp fuses, but you can get reducers that will let you put 100 amp fuses into a 200 amp fuse holder.
 
On a bit of a separate note but related and per the cut sheet attached in my first post.

1. If the hoist FLA is 150A and I wanted to feed from a 208v source and use a transformer I see that a 112.5kva only put outs 135A on the 277/480v side. I would have to utilize 225kva xfrmr? Thank you
 
horsegoer said:
On a bit of a separate note but related and per the cut sheet attached in my first post.

1. If the hoist FLA is 150A and I wanted to feed from a 208v source and use a transformer I see that a 112.5kva only put outs 135A on the 277/480v side. I would have to utilize 225kva xfrmr? Thank you
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Would it damage the 112.5kVA xfmr to source 150A for only as long as it takes for the hoist to get going?
 
horsegoer said:
My question is I believe the secondary side of the xfrmr wouldn't provide enough power( 135A) to power the hoist(150 FLA). Thanks.
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The point of the comment was that transformer ratings may be allowable averages, with brief excursions above the rating allowed, while equipment ratings may be maximums.

Cheers, Wayne
 
horsegoer said:
My question is I believe the secondary side of the xfrmr wouldn't provide enough power( 135A) to power the hoist(150 FLA). Thanks.
Click to expand...
Transformers do not clip their output at their maximum current rating.
 
horsegoer said:
THanks. I think that's a "bucket"/fused switch inside a switchboard. Could we change out the switch to a higher rated?
But then we would have to make sure the distribution board could handle the increased load, correct?

How would one go about that? Demand metering?
Click to expand...

If you add up all the breakers in your house do they exceed the main breaker?

What you are doing is increasing the load. This is always much more complicated and expensive than it seems at first glance. Start at the switchboard. What does another 50 A of load look like? Do you need a load study as NEC requires or can you estimate/calculate it? It’s a hoist, used during production or only when offline?

Second, what slots are available and what sizes will the switchboard take? Are there feeder busbars where you could attach (1) external fused disconnect?

Third, check all the wiring and the secondary disconnect(s). And conduit sizes. And supports. And wall space.

These jobs always have a tendency to explode in terms of scope.
 
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