Min Ckt Ampacity - two circuit heater

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Natfuelbilll

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Just can’t get my head around which Code section applies.

An air handling unit with two electrical “heating circuits” each has a minimum electrical circuit ampacity and corresponding overcurrent rating. Is it correct to simply add the two values together to obtain the branch circuit feeding the two daisychained supplementary overcurrent devices.
 
You can do that but are you certain that the unit doesn't take 2 branch circuits? Usually there is a 60 and a 30 amp breaker in the unit but some require 2- branch circuits.

If you want to calculate the load then my guess is you have a 15kw heater-- if so then you would have 15000/240 x 1.25 = 78 amps so an 80 amp overcurrent protective device would work. Do the math-- I am guessing and add the fan amps also.

Most of the elements I have seen are less than 15kw but with the fan they usually end up being right at 15kw. I think the 10kw is about 9.6kw and the 30 amp (5kw) is 4.???.

You could have 2- 10 kw heaters at 60 amps each.
 
It does have two breakers. It is 15kW three phase. Factory installed breakers are 25A and 35A. Corresponding minimum circuit ampacity is about 21A and 32A (I don’t have the cut sheet on me).

I think these are supplementary breakers. Being so is the breaker in the panel branch breaker, or a feeder breaker?

What section do the rules appear?

Is the unit required to be nameplated as in NEC 440?
 
It sounds like you need two branch circuits run to the unit as the breakers in the unit are supplemental breakers.
 
I'm normally on the same page as Dennis and he may show me the error in my ways but I would have no problem with a feeder being installed and taps to the two breakers. The feeder would need to be protected at the conductors ampacity.
 
a lot of the units i see have a duel or single supply option with manufactures min circuit rating and max over current for both options

Edit what model number who made the unit
 
Natfuelbilll said:
What section do the rules appear?

240
426
420
430
440

?
Click to expand...


It has more to do with what the manufacturer requires. If the unit is designed to accept 2 circuits then you have to run 2 circuits. If the unit has a single buss for the 2- built in breakers than you only need one circuit.

Article 424 is what you should be looking at.

Gus, I agree you can do what you are saying.
 
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