tapered busway

[mshields]

it's a common practice to taper busway as it goes up the building. Does the code discuss the fact that you may therefore have a, e.g. 4000A breaker ultimately protecting a smaller piece of bus? And if so, where is it discussed?

 

[infinity]

I think that the best you could do is a reduction in size where you could apply the tap rules in 240.21.

368.17(C) Feeder or Branch Circuits. Where a busway is usedas a feeder, devices or plug-in connections for tapping off
feeder or branch circuits from the busway shall contain the
overcurrent devices required for the protection of the feeder
or branch circuits. The plug-in device shall consist of an
externally operable circuit breaker or an externally operable
fusible switch. Where such devices are mounted out of
reach and contain disconnecting means, suitable means
such as ropes, chains, or sticks shall be provided for oper-
ating the disconnecting means from the floor.
Exception No. 1: As permitted in 240.21.

 

[ron]

In the past, I have only tapered busway size downstream (rising up the building) of an OCPD.

 

[infinity]

In the past, I have only tapered busway size downstream (rising up the building) of an OCPD.

Unless complying with a tap rule I see that as the only way to do a size reduction as you go up through a building.

368.17(B) Reduction in Ampacity Size of Busway. Overcurrentprotection shall be required where busways are reduced in
ampacity.

 

[GoldDigger]

If you are somehow able to justify using a tap rule, you still can effectively only go one floor.
Protecting a bus to two remaining floors by a distribution OCPD on each floor is not allowed since the tap must terminate on at most one OCPD.

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[mshields]

thank you gentlemen!

thank you gentlemen!

very helpful as always!