Coordination of Essential Electrical Systems

[corvalan]

The NEC 2020 in section 517.31 (G) requires coordination for OCPDs serving essential electrical systems circuits. Is this coordination required in both paths, the normal power (utility) and emergency power (generator) or only through the generator path?

 

[don_resqcapt19]

The way I read that language is that it applies to all overcurrent protective devices, both normal and emergency, that supply the essential electrical system. Note that the coordination required by this section is not the same as the selective coordination that is required by other parts of the NEC.
The health care systems only require coordination down to 0.1 seconds, while the selective coordination rules in the NEC require coordination down to time zero.

 

[d0nut]

Each essential electrical system overcurrent device must be coordinated to 0.1 seconds with every upstream overcurrent device that feeds it, both on the normal and generator sides. The normal breakers, however, are not required to coordinate with the other normal breakers also feeding that essential electrical system device.