lowering main circuit breaker at generator question

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Cartoon1

Cartoon1

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Florida
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Electrical Engineer
Hello all. I came across this particular case where the specified generator for the project is rated 30KW with a 125A main breaker integrated into the generator that goes to auto transfer switch and emergency panels (everything rated for 125A... cables, transfer switch, emergency panel). The contractor says he can get a 40KW similar generator with transfer switch (it is in stock). But the generator integrated main breaker is 175A.

Solutions:
A. Not sure if it possible, but can the integral main breaker at main generator be interchanged with a 125A and keep everything as is. (of course to be verified with generator manufacturer). assuming the manufacturer provides it.

B. Upgrade the cable ratings and emergency panel to 200A

I want to go with Solution A, as it is the easiest option without requiring a change to the system. Is that a feasible option?
Option B will require to change the conduit, panels, and cables (it will take more time to re-order the panels at least)

What do you think is the better option? Does option A have any code violations that you can think of?
 
Cartoon1 said:
Hello all. I came across this particular case where the specified generator for the project is rated 30KW with a 125A main breaker integrated into the generator that goes to auto transfer switch and emergency panels (everything rated for 125A... cables, transfer switch, emergency panel). The contractor says he can get a 40KW similar generator with transfer switch (it is in stock). But the generator integrated main breaker is 175A.

Solutions:
A. Not sure if it possible, but can the integral main breaker at main generator be interchanged with a 125A and keep everything as is. (of course to be verified with generator manufacturer). assuming the manufacturer provides it.

B. Upgrade the cable ratings and emergency panel to 200A

I want to go with Solution A, as it is the easiest option without requiring a change to the system. Is that a feasible option?
Option B will require to change the conduit, panels, and cables (it will take more time to re-order the panels at least)

What do you think is the better option? Does option A have any code violations that you can think of?
Click to expand...
Under option "B", I wouldn't think you need to upgrade the emergency panel, just the cables going to the panel. If even that. The cables from the generator to the panel are protected by the breaker in the emergency panel. The panel can't draw more than the breaker rating, and we assume the cables from the generator to the panel are OK with the panel breaker. If you have a 1,000 megawatt power plant (generator) you're not providing cables to handle all that power to the house, are you?
 
don_resqcapt19 said:
Where is the first OCPD on the load side of the generator?
Click to expand...
Per the OP, it's 175 amps, then you pass through an ATS and get to the emergency panel where there is a 125 amp breaker. Now there is a proposal to install a generator with an OCPD of 200 amps. The question is, which if any equipment/conductors need to be upsized?
 
gadfly56 said:
Per the OP, it's 175 amps, then you pass through an ATS and get to the emergency panel where there is a 125 amp breaker. Now there is a proposal to install a generator with an OCPD of 200 amps. The question is, which if any equipment/conductors need to be upsized?
Click to expand...
Tap conductors?
 
gadfly56 said:
Per the OP, it's 175 amps, then you pass through an ATS and get to the emergency panel where there is a 125 amp breaker. Now there is a proposal to install a generator with an OCPD of 200 amps. The question is, which if any equipment/conductors need to be upsized?
Click to expand...
I guess my real question is; does the ATS have breakers and if so what are they rated at, or is the breaker in the emergency panel the first breaker on the load side of the breaker at the generator.
 
Just wanted to update:
Found out that the generator main breaker 175A can be interchanged with a 125A breaker as an option. So this takes care of everything and nothing needs to get up sized. The load will not exceed 125A anyways and even if it does (from the emergency side) the generator 125A breaker will trip. Also, the emergency panel has a 125A MCB. So the setup now is.... 125A breaker at the generator location, 20FT of cable to the 200A rated transfer switch that connects to a 125A MCB rated emergency panel. Thank you
 
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