Busduct Tap

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Dean83169

Dean83169

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I have a 2500 amp busduct breakered at 2500 amp. The room that was base building built was built so only half the busplugs could be used. The room has been filled with xformers and panels and I have to install a 480v/600 amp gear with a 150 kva trans to a 208v/500 amp gear. Since this will be leaving the busduct room to goto another room and I have no room to install a 600 amp busplug, what options do I have with the code for a tapbox off the busduct with the tap rule because I have room to install this. The local inspector told me to check it out and said I would be able to do this but I know that 1/3 rd of 2500 is about 850 which does not give me the option, am I missing something or is he testing me or does he not know what he is looking at?
 
On older style bus duct, that had the old "power takeoff" type of taps, I have seen installations where they took off part of the enclosure, tapped the bus bars inside it and basically made a makeshift cable tap box. Let me stress that this is OLD, and as an engineer, I'd never specify it.

As for the newer plug-in type of busduct, I've never seen this done. At the very least, I'd think it'd completely invalidate the UL listing of the busduct, and I don't see Square D or GE validating that install.

The better option is to tap the bus on the switchboard and setting an enclosed circuit breaker in the room if you can. It requires shutting down the whole section or maybe the whole board, but if you're not violating a six handle rule, that'd be my first option for the design. If not, then look at the second floor, or somewhere else on the busduct where you can fit it, to put in your 600A bus tap.
 
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It seems to me that if you don't have room for a 600 bus duct switch then you won't have room for a tap, although one is permitted. Can you get a disconnect switch with 25' or less of conductors near the bus duct?
 
Yes I can within 25' but it will be in the next room. I have room for the tap box which I believe square D makes for its newer style busducts. The tap box is a considerable amount smaller to the 480v/600amp fused disconnect I would have to install. Again its a 2500 rated busduct and fused at 2500 amps. I am only running 600 amps off this so I thought I could not run to a different room and it would have to be at least 1/3rd of the 2500amp.
 
Dean,

If there is room for a tap box, then how about using a 90 degree busduct

fitting and adding a section of busduct ? This way you could plug in a 600a

OCPD and all would be factory equipment.
 
I agree with Frank. Install the tap box with 2 sets of 600 kcmil or 3 sets of 300 kcmil THHN cu over to your 600 amp disconnect. You tap conductors are limited to 25' or less.
 
But if I do this doesnt the 25' tap rule prohibit me from installing the disconnect in a different room then the tapbox would be located, or can I run the tapbox with the set of conductors for 850 amp piped through the wall and down to a 600 amp main in the room next to this taproom?
 
tap

tap

Dean, after reading these replies the one that makes the most sense and easiest route is to use a bus duct 90 or "T" w/ a full length of duct to go through the wall, as per 368.10(C). Install tap box above your new 600A OCP.
 
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