Equipment fed from different panels

[Motoarrow51]

I was working on a remodel job recently. They have an electric tankless water heater fed with 3 50 amp circuits feeding the water heater. They have a 90 amp breaker feeding 100 amp sub panel/ disconnect with 2 2 pole 50 amp breakers. And then they have a separate 50 amp breaker feeding a separate disconnect also feeding the water heater. Inspector told my boss that the water heater needs to be fed from two different panels. The house has a 400 amp service with to 200 amp sub panels and he wants the water heater Fed from the two different panels. Everything is located in the garage. the inspector said he wants the 90 amp feeding the two 50A in one panel and he wants the 50 amp feeding the third circuit out of the second panel. I’m not sure I’m feeling this is correct why would you want to feed one piece of equipment out of two separate panels. Any feedback will be appreciated

 

[petersonra]

Maybe the load calculation on one panel does not allow for the full load of the water heater. When you installed it you did do a load calculation right?

 

[infinity]

What is the total load on the 3-50 amp circuits? Sounds like the 90 amp feeder too small for that load so it really isn't about him wanting you to use two different panels it's just that the 90 amp feeder not adequate for the load.

 

[AC\DC]

Never done this before. Can you run from two different sources to one equipment??? Probably an exception. Never had to look this up yet.

 

[jim dungar]

Never done this before. Can you run from two different sources to one equipment??? Probably an exception. Never had to look this up yet.

It is a not uncommon in industry. Warning labels saying there two sources of power available are definitely suggested.