LRA and circuit breaker rating

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Old 06-09-13, 05:08 PM
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LRA and circuit breaker rating

Hey guys, quick newbie question. I'm just researching generators for back up power and need some clarification on the breaker for my a/c condensor. It's rated at 80 Amps and I noticed the LRA on my condensor is 129 amps. From what I'm reading the LRA is the amount of current being pulled at start up correct? Why isn't it tripping the 80 amp breaker? Thanks
 
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Old 06-09-13, 08:12 PM
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Welcome to the forums!

I'm just researching generators for back up power and need some clarification on the breaker for my a/c condensor. It's rated at 80 Amps and I noticed the LRA on my condensor is 129 amps. From what I'm reading the LRA is the amount of current being pulled at start up correct? Why isn't it tripping the 80 amp breaker?
LRA, or Locked Rotor Amperage, is the same as inrush amperage. Yes that's the amperage being used at startup.

FLA, or Full Load Amperage, is the current used once the condenser is running. Many pros divide the LRA by 6 to estimate the FLA if it isn't stated.

Most standard circuit breakers are designed to allow an overcurrent condition to exist within certain parameters - so long as it isn't too large and if it doesn't last too long. That's what your 80 amp breaker is doing.

Why so large a breaker? What is the size of the wire it's protecting? What is the stated FLA of the unit?
 
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Old 06-10-13, 04:53 PM
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Why so large a breaker? What is the size of the wire it's protecting? What is the stated FLA of the unit?
I am more interested in how many tons of cooling this unit is rated for. Sounds as if it could be a 7 1/2 ton machine.
 
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Old 06-11-13, 02:06 PM
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Thanks guys, you answered my question about the breaker. It's actually a 4 ton 48,000 BTU unit which is connected to a double breaker with 40 amps on each side, not an 80 amp breaker like I originally posted. I'm surprised that 40 amp breakers will allow that very short burst over 100 amps without tripping, but I guess you are saying that is how they are designed.

I've also deduced that my generator will not even come close to handling the LRA on that unit, which is 129 amps, but may be able to handle my smaller 2 1/2 ton unit with the help of a hard start capacitor. I have a 7500 watt gen with 9325 surge watts.

Nashkat1, it's says the RLA is 23.7 and the FLA is 1.5? But again, I'll be trying to power the smaller of the two with my generator and a hard start capacitor.
 
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Old 06-11-13, 04:04 PM
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it's says the RLA is 23.7 and the FLA is 1.5?
That's for the smaller unit, right? JOC, what are those values for the 4 ton unit?

A/C condensing units are no small load. With a small generator, some ceiling, floor and window fans might be good investments.
 
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