Selective Coordination NEC 700.27

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Larry G

Member
I am wiring a surgery clinic in an existing building with a 277/480 volt service. A breaker in the MDP feeds a 225KVA TX in the surgery suite. beyond tht is a 120/208 volt subdistribution panel which feeds among other things, A transfer switch and 3 branch panels of the emergency system. We also have an emergency generator.
How far back does selective cooridination need to go to be effective?
To the secondary TX?
To the transfer switch?
To the breaker in the MDP?
 

steve66

Senior Member
Location
Illinois
Occupation
Engineer
From the NEC handbook:

This coordination must be carried through each level of distribution that supplies power to the emergency system.

That seems to agree with what Ron said.
 
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