Tap conductor sizing options? Industrial wiring

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davaravid

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I have a 1600 amp breaker supplying a group of cabinets that each feed electric heating elements. The 1600 amp breaker feeds 9 conductors (3 per phase). Each of the existing heating element cabinets has a 500 amp breaker. The 500 amp breakers are fed by tap conductors that go to the main feed conductors. I would like to install two new cabinets, but they each only have a 250 amp main breaker. I would like to tap off the same main supply conductors as the other cabinets. The problem I run in to is the tap conductor sizing. Since the cabinet is 20 ft away from the main supply conductors (greater than 10 ft), I have to upsize it. The problem is that the appropriately sized conductors won't fit into the lugs of the 250 amp breakers. Can anyone think of a way around this? I would like to size the tap conductors for being 10 ft long, but in actuality they will be 20 ft. The main supply conductors are in an open-air tray up high. The tap conductors drop down out of the tray with their own conduits into the cabinets. This is an industrial setting. Below is a rough diagram:


Main supply conductors
======================== (A Phase - 3 conductors per phase)
========================(B Phase - 3 conductors per phase)
========================(C Phase - 3 conductors per phase)
|||............|||..............|||
|||............|||..............|||
|||............|||..............|||
500A Bkr 500A Bkr 250A Bkr
Cabinet Cabinet Cabinet (would like to install)
 
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Disregard NEC?

Disregard NEC?

If I wanted to disregard the NEC code on tap conductors... and use wire sized as it if fell under the 10 ft rule... does anyone know the proper way of doing this? Do I have to document the installation?
 
Instead of ignoring the NEC, have considered using any of anumber of available methods to connect larger conductors to smaller devices?

Does your breaker have an option for different size lugs or studs for compression ones? Oversized lugs are a common need with larger conductors used to combat voltage drop. There are even some compression adapters that reduce wire sizes.
 
You might want to consider installing a larger rated fused disconnect with lugs sized for the tap conuctors ahead of the new control cabinet. You could then install 250 amp fuses and use smaller conductors to the new cabinet.

Rick

what size conductors are you using from the 1600 amp breaker that supports only 3 parallel conductors per phase???
 
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RUWired said:
You might want to consider installing a larger rated fused disconnect with lugs sized for the tap conuctors ahead of the new control cabinet. You could then install 250 amp fuses and use smaller conductors to the new cabinet.

Rick

what size conductors are you using from the 1600 amp breaker that supports only 3 parallel conductors per phase???
Click to expand...

I believe the conductors are 500 kcmil, XHHW, run in open air. The breakers are 1600 amp, but have a 1200 amp long time trip setting.
 
The 1600 amp feeder wires can be tapped up to 25ft. by a conductor that is not less than 1/3 of the 1600 amps which is 533 amps.
Parallel 300 kcmil would be required to the main breaker in the cabinet. However, you are right, the conductors won't fit in the breaker.
If you parallel 3 - 3/0 per phase you would need a main breaker that would accept 3 conductors per phase.
I agree with davaravid. Go to a larger disconnect. Then on the load side the conductors could be fused down.
 
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