Switchboard - ground fault protection for fused switches?

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anbm

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Designer
I think I asked this question before, anyway, I hope someone can have more detailed answers for me this time:

We plan to have 4,000A service switchboard (480V/3PH, 4W+G) serving healthcare facility. This switchbaord shall have 4,000A main and below branches:

3,000A
1,600A
1,000A
800A
(2) 400A
(2) 250A


The owner wants to have main and all branch feeder protections in main switchboard to be fused switches , no breaker is allowed.

Any panels downstream of main switchboard, they are okay to go with breakers. My understanding is we need to comply with NEC article 517 for two levels of ground fault protection rule. How do we specify fused switch to comply with NEC and satisfy above owner's desire? Any detailed recommendations shall be great appreciated especially con and pros of CB using vs. fused switches.
 
Any specific model# (fuse switch + relay) to reflect above condition? Thanks!
 
All the major OEM's make them, I stock hundreds of them.

Why dont they want to use breakers? Unusual for a healthcare facility.
 
anbm said:
saving cost and they loved fuse so much, I guess... j/k
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It may be difficult for them to meet the NEC selective coordination requirements if they mix fuses and breakers. Make sure that a selective coordination study has been performed prior to bidding so that you know at least one manufacturer can actually supply a system that meets both your design and the applicable codes for the emergency systems.
 
Have you considered the arc flash incident energy consequences when using fuses vice circuit breakers? Also, you haven't mentioned what type of fuses you to use. You might consider KTU fuses as a means of reducing incident arc flash energy. But, you still have to do a coordination study to determine the effects of various types of fuses with the selective coordination.
You can use ground fault protection for the bus using bolted pressure switches as mentioned in another reply.
 
Pringle with ITI Zone Selective relays.
Bolt Switch wit ITI Zone selective relays
Square D BoltLoc with Square D, GC or GP GFP relays.
 
The smallest fuse can be installed inside bolted pressure switch is 800A, is this correct?
 
anbm said:
The smallest fuse can be installed inside bolted pressure switch is 800A, is this correct?
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No.

That old restriction is one reason that the silly 601A Class L fuse exists.
But, today it is possible to get Class L fuses all the way down to 150A (i.e. the Bussmann KRP-CL series).
 
Does your client know what it will cost to replace blown fuses in those disconnects? Are they willing to stock spares of each size? Granted, they should never blow, but we know that never happen sometimes, and usually at the start of a long weekend.
 
zbang said:
Does your client know what it will cost to replace blown fuses in those disconnects? Are they willing to stock spares of each size? Granted, they should never blow, but we know that never happen sometimes, and usually at the start of a long weekend.
Click to expand...

Does your client know the difference in cost of a bolted pressure switch replacement when the solid state trip unit fails? Oh wait they do not have solid state trip units.

4000 amp bolted pressure switch 6,000.00, 4000 amp circuit breaker 28,000.00-32,000.00 NEW.
 
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