Emergency circuit coordination

[olc]

Thinking aloud a little:
A 80KW generator with separate emergency lighting transfer switch and a optional system transfer switch. The main circuit breaker, optional system tranfer and optional system panelbd would be 200A while the emergency transfer and panelbd would be 100A.
The emergency circuit circuits breakers need to coordinate with the main circuit breakers. I'm not sure the optional system branch circcuit breakers need to coordinate but they must because we sure do not want the main CB opening due to something in the optional system. I was think that a fused safety switch on the line side of the optional system transfer switch would be a good insurance.

On the other hand I can use a separate 100A main circuit breaker at the generator for the emergency system and there would not be a problem. (the only issue is that it is a fair distance from the generator to the transfer switches to run two feeders)

The above should be fairly common. How have you handled it?

 

[Gregg Harris]

Thinking aloud a little:
A 80KW generator with separate emergency lighting transfer switch and a optional system transfer switch. The main circuit breaker, optional system tranfer and optional system panelbd would be 200A while the emergency transfer and panelbd would be 100A.
The emergency circuit circuits breakers need to coordinate with the main circuit breakers. I'm not sure the optional system branch circcuit breakers need to coordinate but they must because we sure do not want the main CB opening due to something in the optional system. I was think that a fused safety switch on the line side of the optional system transfer switch would be a good insurance.

On the other hand I can use a separate 100A main circuit breaker at the generator for the emergency system and there would not be a problem. (the only issue is that it is a fair distance from the generator to the transfer switches to run two feeders)

The above should be fairly common. How have you handled it?

700.27 Coordination. Emergency system(s) overcurrent devices shall be selectively coordinated with all supply side overcurrent protective devices.
Exception: Selective coordination shall not be required between two overcurret devices located in series if no loads are connected in parallel with the downstream device.

 

[steve66]

If there is a single main in the generator, then yes, the optional breaker would have to coordinate to make sure it doesn't take out the main from a fault on the optional system.

Then the 200A breaker for the optional system and the 100A breaker for the emergency system have to be in separate enclosures or separate vertical switchboard sections.

I usually just specify 2 breakers on the genset. It seems like a fairly easy option for most generator manufacturers to do.