Switchgear tap

[larmee]

I have an existing switchgear with a spare 350 ampere breaker.
I need to install a 200 ampere disconnect off of this existing gear. The tap is less than 10 feet and I need to know what the options are for using this existing breaker. If I do use the breaker will the disconnect have to be sized to 400 ampere and fused at 200. Would it be more advent adventageous just to tap the bus according to the 10 ft tap rule in 240.21

Thanks

 

[zog]

What type of breaker? (Not brand, type, as in model)

 

[larmee]

Unfortunately unknown at this time

 

[augie47]

I assume zog is looking at the possibility of changing the trip unit in the breaker, most likely the easiest solution.
Tapping the buss is normally not acceptable unless you have authorization from the manufacturer which in my experience is almost an impossible task.
As far as the tap rule, it is Code permissible for you to terminate your conductors in a 200 amp disconnect.

 

[iggy2]

I would use the existing 350A CB, run 350A wire to the 200A disconnect, then run your feeder from there at 200A. IMO the disconnect only need be rated 200A. The tap starts at the line lugs on the disconnect, and ends at the load lugs.

You should avoid tapping the buss, for the reason noted above.

I suppose you could call the wires off the 350A CB a tap, and make them 200A, but that would probably tend to raise the question of why there is 200A wire on a 350A CB. You and the EC will spend more $$$ in time explaining it's a tap, which just happens to be connected at a CB, than the upsize in wire will cost.

You could also change the CB, but in most cases, with older gear, it is impossible to prove what CB is UL llisted for use in that gear. Not to mention the cost of the breaker, which would be offset only slightly by not having to buy the disconnect.