Generator breaker sizing

[hhsting]

I have 350kW generator 480V three phase that has one 400A breaker and another 600A breaker. 400A feeds optional standby and 600A feeds emergency branch and fire pump. Fire pump is 30HP at 480V three phase.

My question is their anything in NEC 2017 that regulates or says in regrading the above type generator breakers sizing? Aren’t they oversized?

 

[augie47]

445.12 requires the generator have overcurrent protection. It is highly probable that yours will have overloadm protection by inherent design.

 

[hhsting]

445.12 requires the generator have overcurrent protection. It is highly probable that yours will have overloadm protection by inherent design.

So one can size the breaker whatever size they want?

 

[Engser18]

So one can size the breaker whatever size they want?

For Fire pump, you are also need to look at 695 and sized the CB IAW with that section.

 

[jap]

To me the generator itself is under sized.

JAP>

 

[Engser18]

To me the generator itself is under sized.

JAP>

As I recall, the generator sized base on the Max of either all the load or fire pump load.

 

[Birken Vogt]

The generator is sized to the calculated load by various factors.

The breakers on the generator are sized to protect the wires they are connected to in accordance with the NEC for wire size

The generator was probably custom ordered with those size breakers to fit the application. What do the plans and engineering say?