Motor contribution central air conditioners and series rating in residential buildings NEC 240.86(C)(2)

[electrofelon]

There is no motor connected to the branch circuit. How could there be a motor contribution.

each apartment has a branch circuit with central AC. Central AC is connected to branch circuit and therefore is part of the motor contribution

I think both of you are mistaken. First note we are talking about motor contribution disallowing a series rating. That is different then a general available fault current calculation considering motor contribution. Look carefully at the wording in 240.86(C)(1). I see 14 motors under consideration for disallowing a series combination.

 

[PD1972]

... I see 14 motors under consideration for disallowing a series combination.

I think it's 14 motors too.

I believe the panels inside the apartment units can stay at 10kAIC?

Is this supposed to be a 3-tier series rating?

 

[don_resqcapt19]

2023 NEC.

Significant change between the 2023 NEC and the 2020 NEC. 2020 NEC says "and." 2023 deleted and and now it reads as "or". Oddly the change appears in the 2023 First Draft with no associated PI or substantiation, something I've not seen before.

Cheers, Wayne

it appears to me that was NFPA staff trying to make editorial changes to comply with the style manual, but they made a prohibited technical change.

 

[petersonra]

Since it does not say "and" or "or" there is no way to determine how it should be read unless the style guide provides a clue.

 

[electrofelon]

So lets say each motor FLA in the apartment is 40 amps, this means (15) 2-pole apartments per meter bank will have a total of 600 FLA for the motors combined.

Does this mean that each 2-pole breaker inside the meter bank need to be 65kAIC?

I believe the panels inside the apartment units can stay at 10kAIC?

Sorry we have been alll over the place with the wording. Also in the beginning I said there was no issue, I was thinking about it wrong and had to draw it out. So other than the quantity being 14 and not 15, and assuming the 40A figure is correct, then yes i agree with you the downstream device needs to be 56K minimum. I dont see an issue with the 10K appartment breakers unless this was a triple rating.

 

[jim dungar]

Did the UL Listing requirement change? If not it needs to be followed regardless what the NEC says.

 

[Tainted]

Sorry we have been alll over the place with the wording. Also in the beginning I said there was no issue, I was thinking about it wrong and had to draw it out. So other than the quantity being 14 and not 15, and assuming the 40A figure is correct, then yes i agree with you the downstream device needs to be 56K minimum. I dont see an issue with the 10K appartment breakers unless this was a triple rating.

Why 14 and not 15?

 

[electrofelon]

Why 14 and not 15?

Each series rated set will have a motor downstream from the lower rated breaker thus not in the location as required by 240.86(C)(1)