Air Conditioner Panel

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RichardHebl

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I need to calculate the size of a 120/240V 1PH feeder to a panel that will contain the breakers for 3-A/C units: 2-5 Ton (35A min circuit, 50 amp max breaker) and 1-4Ton (24A min circuit, 40 amp max breaker). Can I use the
min circuit ampacity since it is calculated by the full load of the compressor
X 1.25% plus the fan motor? Will a 100 amp feeder be large enough (35+35+ 24 = 94)?
Let me clarify that the branch circuit selection currents of 35A and 24A are taken off the nameplate rating of the A/C unit and I believe are figured using the compressor FLA X 1.25% and then the fan FLA is added to this to come up with the total branch circuit amperage of each unit. My question is not about the disconnects for the units but about the size of the circuit breaker and feeder that will be supplying power to the panel for all 3 A/C units.
 
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Dennis Alwon

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Chapel Hill, NC
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Retired Electrical Contractor
RichardHebl said:
I need to calculate the size of a 120/240V 1PH feeder to a panel that will contain the breakers for 3-A/C units: 2-5 Ton (35A min circuit, 50 amp max breaker) and 1-4Ton (24A min circuit, 40 amp max breaker). Can I use the
min circuit ampacity since it is calculated by the full load of the compressor
X 1.25% plus the fan motor? Will a 100 amp feeder be large enough (35+35+ 24 = 94)?

What about the fan motor and 125% of the largest motor? 100 amp won't do it.
 

Cavie

Senior Member
Location
SW Florida
Minimum circuit amps for A/C compis only for branch circuits only. You are figureing feeders sooooooo. You gotta do feeder calcs. sorry
 

augie47

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Location
Tennessee
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State Electrical Inspector (Retired)
A/c

A/c

Different opinion... In my opinion, as far as the feeder, the MCA already has any required multipliers so if the fan motors don't add enough to tjhe 94 amps to go beyond an ampacity of 100 amps the feeder should be sufficient. The disconnect rating, however, must be 115% of the branch circuit selection current.
 
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