coordination of generator for 0.1 (per 517 requirements) and/or 0.01 for Emerg apps

[mshields]

A colleague did a design where he had a 125kW generator with a hospital Type 1 EES. Because of the size of the generator, he's having a difficult time coordinating his life safety and critical branches with the 225A breaker he plans to specify on the output of his generator. I've gotten around this in the past by not providing a main breaker in keeping with Article 240 and the clause in 445 which states you can do that if conductors are rated at 115%.

He's telling me that the internal protection provided with the generator is still a factor and that it is still seemingly impossible to attain the needed selectivity.

Would be interested in your experiences in similar situations?

Thanks,

Mike

 

[charlie b]

He's telling me that the internal protection provided with the generator is still a factor and that it is still seemingly impossible to attain the needed selectivity.

What exactly is meant by "internal protection"? You can selectively coordinate breakers and fuses in various combinations. But I don't believe any other type of device is required to play in that arena. My preference is to leave out the generator breaker and connect to something that allows you to keep the pathways separate for the 700, 701, and 702 loads. Examples are a wiring gutter with separate enclosed breakers beneath it or a switchboard with separate vertical sections.

 

[mshields]

helpful as always!

helpful as always!

Thank you

 

[lielec11]

Going a bit off topic but if you're not using a generator main, what is in place to protect the generators motor? What do you use to compare against the decrement curve?

 

[charlie b]

. . . what is in place to protect the generators motor?

I infer that you meant "generator's windings." The sum total ratings of the downstream circuit breakers will be lower than the generator's rating. They will protect the windings.

 

[Sahib]

The sum total ratings of the downstream circuit breakers will be lower than the generator's rating. They will protect the windings.

[]

A fault in winding itself will not be seen by those breakers. A sophisticated protection such as differential protection will do it and protect the generator from further damage.