Oddball Tap Rule Question

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salm10

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I have to make a tap off a 2500 amp switchboard, but I only need 400 amps and the tap is going to be more than 10 feet in length. So I am proposing that I use 1000 amp conductors, terminating in a 1200 amp breaker with a 400 amp trip unit. From there, I will run a single set of 500's to a distribution panel. Does my 400 amp trip setting on the breaker meet the intent of 240-21? Thanks in advance for you input!
 
Less than 25 ft ??
You could use tap conductors rated 834 amps..a little better than 1000.
If your trip unit is non-adjustable, IMHO, you are in compliance (if your method of tapping is approved.).
 
Given the breaker had the proper terminals, couldn't he use a 400 amp breaker with conductors having an ampacity of 834 amps? Seems like there may be a big cost difference between a 1200 amp frame/400 amp trip CB and a dual lug 400 amp.
 
The breaker is only available with an adjustable trip unit, but it will be behind a clear plastic plate to prevent unauthorized tampering. I would have gone with a 400 ampere breaker, but I cannot find one with lugs suitable for three conductors per phase, so that forced me to use a 1200 amp frame breaker. And to Infinity, yes, the cost difference over a 400 is big unfortunately. But I don't see a way around this. As it is, I think it meets the intent of the code but I thought I would toss the concept to others who are in authority here.
 
salm10 said:
The breaker is only available with an adjustable trip unit, but it will be behind a clear plastic plate to prevent unauthorized tampering. I would have gone with a 400 ampere breaker, but I cannot find one with lugs suitable for three conductors per phase, so that forced me to use a 1200 amp frame breaker. And to Infinity, yes, the cost difference over a 400 is big unfortunately. But I don't see a way around this. As it is, I think it meets the intent of the code but I thought I would toss the concept to others who are in authority here.
Click to expand...


I was thinking a 400 amp with double 600 kcmil lugs. Don't know if they are available however.
 
perhaps a 400 amp breker with dual 500 lugs and these reducers:
http://portal.fciconnect.com/portal/page/portal/FcicntPublic/Product_Type?appname=catLanding

if not, and I was going to that expense, I think I'd opt for a 600 or 800 amp panel so you will have avaialble space the next time you need to add.

(sqaure D does show M frame with lugs (optional) for (2) 600s... a bit better thanj your 1200 amp)
M-, P-Frame
800 A
—
MJ
800 A
(2) 3/0 AWG-600 kcmil
 
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Pierre C Belarge said:
Is it possible to move the tap location somewhat closer to the supply, to take advantage of the 10ft rule?

What about adding a 400 amp switch in the gear?
Click to expand...
Great pair of suggestions, in the "Why didn't I think of that?" category.

I have a funny feeling there are already answers to Pierre's questions as to why not.
 
Could you use a 800 amp fused disconnect with fuse reducers and 400 amp fuses in place of the breaker? I would guess it would be cheaper, and at least one manufacturer has it with terminations for 3 3/0 through 750kcmil conductors.
 
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