I have run across a few of these lately and have received different feedback form other professionals, so I thought I would ask here. I have a heater that has a 50A breaker. The manufacturer calls for a 60A max breaker with a 53A min circuit ampacity. The heater is 40A. So it is my understanding that the wiring should be for a min 53A, the breaker should be at least 53A with a max of 60A. Is this correct or is a 50A breaker sufficient since the heater is only 40A? TIA…Photo wouldn’t upload for some reason.
Max breaker is as it sounds. No min breaker. The 50A is fine.
Min circuit ampacity only relates to the wire sizing.
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I’ve discussed this with other electricians with varying opinions but IMO the unit is calling for a 53 amp conductor but also a minimum of a 53 amp circuit. 50 amps is less than the minimum circuit ampacity required.
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This is the feedback I have received from my electrician and hvac guy as well, but others have stated when Michael said. My questions would be if 50A is ok, why would the wire size need to be 53A?
My argument as well. The conductor size is typically figured by taking 125% of the heating load and adding the other ancillary loads to that at 100% each. So you may end up with (40)(125%) = 50 amps + 3 amps of other loads, controls, etc. If you simply go by the exact wording on the nameplate minimum circuit ampacity that would mean 53 amps in this example. The wording in the NEC is less than clear.
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What would happen if the maximum breaker size is 50 amps and a 25 amp breaker was installed in the panel? Would the unit operate?
What would the smallest breaker be?
Another good argument. If you can ignore the MCA completely when sizing the OCPD then use any size CB that you have on the truck. 
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