Switchgear common bus sizing- split groups of gen for smaller bus sizing?

[tumbleweed1]

Say we have two groups of 2 generators, each group capable of 4000A output. And we connected the load/utility line to the middle of the bus between each group. Can we get away with sizing each generator switchgear bus to 4000A each, and simply have a middle transition cell with 8000A of bussing?

I'm envisioning cell 1 and 2 each with 4000A common bus, cell 3 the transition cell and outgoing with 8000A bus, and cell 4 and 5 with 4000A common bus.

As per Canadian Electrical Code, this seems to suit 14-100.

Would this be a correct way of doing things?

 

[waross]

Have you considered rule#
84-010 Overcurrent protection
Equipment and conductors that are energized from both directions shall be provided with overcurrent protection
from each source of supply.
A full length 8000 Amp bus will be protected by the outgoing breaker and by the generator breakers.
However in the event of a back feed, this rule appears to require protection at the reduction points from 8000 Amp bus to 4000 Amp bus.
You may be granted relief by rule#
14-100 Overcurrent protection of conductors
(b) where the smaller conductor
(i) has an ampacity not less than the combined computed loads of the circuits supplied by the smaller
conductor and not less than the ampere rating of the switchboard, panelboard, or control device
supplied by the smaller conductor;
(ii) is not over 3 m long;
(iii) does not extend beyond the switchboard, panelboard, or control device that it supplies; and
(iv) is enclosed in non-ventilated raceways, armoured cable, or metal-sheathed cable when not part of
the wiring in the switchboard, panelboard, or other control devices;


That said, the AHJ will provide the final answer.
I would attempt to discuss this with a senior Electrical Inspector.


Bill
--------------------
"Why not the best?"
Jimmy Carter