On demand water heater

[Tom Drake]

I have a 150amp on demand water heater to hook up. Three separate 50amp circuits feeding it. What is the proper way to provide means of disconnect for this unit. I was thinking of using three shunt trip breakers

 

[GoldDigger]

I have a 150amp on demand water heater to hook up. Three separate 50amp circuits feeding it. What is the proper way to provide means of disconnect for this unit. I was thinking of using three shunt trip breakers

For OCPD, there does not seem to be any reason to require simultaneous trip since a fault in one set of heat elements is not likely to affect the others.
But for disconnect and LOTO, the three breakers would have to be handle tied or otherwise associated to ensure that power is disconnected to all elements at the same time. A shunt trip would allow a single control button or switch to trip them all but would not prevent one from being re-energized without energizing all them. Not sure how you would provide a lockout for three breakers in a clean way.
Would it be practical to feed the three 50 amp circuits from a subpanel with a single main, or to provide a multipole disconnect switch affecting all three circuits?

 

[texie]

I have a 150amp on demand water heater to hook up. Three separate 50amp circuits feeding it. What is the proper way to provide means of disconnect for this unit. I was thinking of using three shunt trip breakers

I think you are making this more complicated than need be. You can have multiple disconnects as long as they are grouped and identified. See 422.30.

 

[jumper]

I think you are making this more complicated than need be. You can have multiple disconnects as long as they are grouped and identified. See 422.30.

AFAICT, yep.

III. Disconnecting Means
422.30 General. A means shall be provided to simultaneously
disconnect each appliance from all ungrounded
conductors in accordance with the following sections of
Part III. If an appliance is supplied by more than one
branch-circuit or feeder, these disconnecting means shall
be grouped and identified as the appliance disconnect.