Air Conditioner breaker

hardworker

Senior Member
If the condenser label states minimum breaker 21 amps and maximum breaker 35 amps, what awg wire size should be ran to the outside disconnect? What size breaker should be installed in the panel?

I am getting some confusing statements from an inspector. Please clarify.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
If the condenser label states minimum breaker 21 amps and maximum breaker 35 amps, what awg wire size should be ran to the outside disconnect? What size breaker should be installed in the panel?

I am getting some confusing statements from an inspector. Please clarify.
The nameplate will also tell you the minimum ampacity for the conductors.

I would be inclined to put in the CB that would be least likely to give me trips. Hint - that would be a 35A CB if one is available for the panel you are powering it from.
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
If the condenser label states minimum breaker 21 amps and maximum breaker 35 amps, what awg wire size should be ran to the outside disconnect? What size breaker should be installed in the panel?

I am getting some confusing statements from an inspector. Please clarify.
On something like that it will likely give you that MCA (Minimum Circuit Ampacity) and MOCP (Maximum Over Current Protection). I'd hazard a guess that you are misinterpreting the MCA of 21A as being the "minimum circuit breaker amps", it is not; it is the minimum CIRCUIT amps, meaning you must run conductors rated for a minimum of 21A. Then you calculate the actual wire size based on your other conditions such as voltage drop, number of conductors etc. Once you get your conductor size, then you size the breaker to protect it, but that breaker (or fuses) cannot be larger than 35A.
 

480sparky

Senior Member
Location
Iowegia
No nameplate would list 21 amps as an overcurrent minimum as there are no 21 amp fuses or breakers. I'm with the others.... 21 amps is the minimum circuit ampacity.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
For conductors you can use #12 AWG with a 35 amp OCPD if you have conduit and wire or MC cable. If you're using NM cable then you would need #10 AWG
 

hardworker

Senior Member
For conductors you can use #12 AWG with a 35 amp OCPD if you have conduit and wire or MC cable. If you're using NM cable then you would need #10 AWG
What happens to the #12awg wire if it pulls 30 amps for some reason and it is protected in the panel with the 35 amp breaker as you suggested? The breaker will not open and the #12 can only carry 20 amps. Please explain this to me for my knowledge.
 

GoldDigger

Moderator
Staff member
...
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Once you get your conductor size, then you size the breaker to protect it, but that breaker (or fuses) cannot be larger than 35A.
Actually, as long as the wiring is presumed to be protected by the motor overload device, you do not have to size the breaker to protect against anything but short circuits and ground faults
That means that if your wire, after corrections and adjustments, is rated for say 24A (higher than 21) you can still use a 35A breaker.



Sent from my XT1585 using Tapatalk
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
Actually, as long as the wiring is presumed to be protected by the motor overload device, you do not have to size the breaker to protect against anything but short circuits and ground faults
That means that if your wire, after corrections and adjustments, is rated for say 24A (higher than 21) you can still use a 35A breaker.



Sent from my XT1585 using Tapatalk
Which is part of the basis for the MOCP listing.

But #12 only works for a 21A MCA if you don't need to factor in VD and # of CCCs...
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
What happens to the #12awg wire if it pulls 30 amps for some reason and it is protected in the panel with the 35 amp breaker as you suggested? The breaker will not open and the #12 can only carry 20 amps. Please explain this to me for my knowledge.
For #12 THHN using the wiring methods in post #6 the conductor ampacity is 25 amps. The unit will not damage those conductors even with a 35 amp OCPD ahead of the branch circuit because the motor itself has integral protection.
 
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