roof condenser and ac unit branch circuit ampacity

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h1h2h3

Member
Location
MA
I am wiring a split sytem mitsubishi (mr. slim) AC unit 208/single phase and i am confused about the branch circuit calculation. the unit has a condenser with fan motor on the roof and an ac inside the office (which is fed off of the condenser circuit.) The R.L.A is 12 amps, the L.R.A. is 17.5 amps, the fan motor is .4 amps, and the ac is .5 amps. The minimum circuit ampacity for the condenser is 25 amps and 1 amp for the a.c. the installation manual states that the min wire to be run to the condenser is A #10 and the max mopd is 40 amps. now my question is, can i use the minimum and run a 30 amp circuit with 30 amp time delay fuses and a 30 amp breaker or would i have to follow 440.33 (1.25*25+.4+.5= 32.15a) and run a #8 then follow 430.53 (17.5*1.75= amps) and install 35 amp time delay fuses and protect the cirucuit with a 40 amp breaker. obviously i am confused about this and would appreciate an explanation on how to properly calculate and size the wiring, disconnect, and ocpd. thank you all.
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
would the fuses in the disconnect be the same as the feeder ocpd?
As long as either the feeder or the disconnect has protection that does not exceed the mfg max ocp, you are fine.
If your feeder breaker is a 40, the disconenct could be a 100... or NoFuse


what about 240.4 for #10 30 amps or are motor circuits the exception?
240.4(D) refers you to 240.4(G) which includes Art 440
 

h1h2h3

Member
Location
MA
thank you all very much for the help.......if i could be a pain for just one more moment....is the ocpd based on 430.52 which would be the LRA multiplied by the given table value?:confused:
 
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