Any Air Conditioning Experts?

AbsolutDealage

Platinum Member
Dec 20, 2002
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I have a slight problem. I currently have 100A service to my house. That seems to be enough most of the time, but 3 or 4 times I have had the 100A breaker trip while the A/C is starting up.

This is (obviously) in situations where a lot of other stuff is running in the house, so it is at least feasible that I am going over 100 on the startup of the compressor (without breaking any of the individual breakers).

I am wondering what can be done to remedy this. I know that there are start up kits / capacitors that you can buy, but I am a little confused as to what I actually need. It seems like most of the kits are meant to start a stuck capacitor, and then take them out of the circuit.

In short, I need something to reduce the startup current on the A/C so that my whole house doesn't lose power. Help!
 

shilala

Lifer
Oct 5, 2004
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Replace the 100 amp breaker after you test the load across it.
My guess is that it's junk.
It happens.
 

JinLien

Golden Member
Aug 24, 2005
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Depends on what you have running during the initial AC start up. The moderate older home tend to have 100A service which isn?t enough for current home electronics/appliances, therefore most newer home have 200A service.

Best way to go is fork out the money for an additional 100A line & panel. Or, fork out even more money to go for a geothermal heat pump system that draws 50-75% less power than your current setup.

 

Rubycon

Madame President
Aug 10, 2005
17,768
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What's the LRA of your CAC compressor? LRA or Locked Rotor Amperes is what the compressor motor will draw when the shaft is not turning. This happens every time the unit starts. If the unit is turned off abruptly and restarted - and a plethora of things can cause this. (From momentary power outages, wife and husband arguing over too/hot too cold with frequent passes of the thermostat dial, to a child curious with a vibrating electric toothbrush on the HEAT/OFF/COOL switch!) A time delay relay (TDR) prevents the compressor contactor engaging until the system's pressures have equalized allowing the unit to start normally.

A good circuit breaker has a time delay built in that will allow an inrush current over its maximum rating to allow for large PSC motors to start and even large banks of tungsten lamps to be turned on! If the breaker is defective it will trip much faster. If it's hot, the time before it trips during an inrush event will be shorter as well.

Is the run long? Lugs on everything *TIGHT*? How hot is the main CB when everything is running?
 

Analog

Lifer
Jan 7, 2002
12,755
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I don't understand why your main is tripping, and not the breaker to the AC. It could be that you have a faulty main, and that's it.
 

skyking

Lifer
Nov 21, 2001
22,007
4,765
146
Originally posted by: Analog
I don't understand why your main is tripping, and not the breaker to the AC. It could be that you have a faulty main, and that's it.

Go tally up your breakers and compare to the main. Every house is 'oversold', so to speak. The sum total of breakers is greater than the main, so large but acceptable loads on every circuit will break the main. That said, I agree with shilala, (grudgingly :p) and think the OP should check the actual load when it trips. I suspect a bad main also.
 

WiseOldDude

Senior member
Feb 13, 2005
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Local government (city or county) allowed you to add air with that puny 100 amp service? Today 200 is considered minimal and 400 is not uncommon.
 

AbsolutDealage

Platinum Member
Dec 20, 2002
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Originally posted by: WiseOldDude
Local government (city or county) allowed you to add air with that puny 100 amp service? Today 200 is considered minimal and 400 is not uncommon.

Well, the house was built in 1921, so I had very little to do with it. I would imagine that the A/C was put in quite some time ago.

Originally posted by: MS Dawn
What's the LRA of your CAC compressor? LRA or Locked Rotor Amperes is what the compressor motor will draw when the shaft is not turning. This happens every time the unit starts. If the unit is turned off abruptly and restarted - and a plethora of things can cause this. (From momentary power outages, wife and husband arguing over too/hot too cold with frequent passes of the thermostat dial, to a child curious with a vibrating electric toothbrush on the HEAT/OFF/COOL switch!) A time delay relay (TDR) prevents the compressor contactor engaging until the system's pressures have equalized allowing the unit to start normally.

A good circuit breaker has a time delay built in that will allow an inrush current over its maximum rating to allow for large PSC motors to start and even large banks of tungsten lamps to be turned on! If the breaker is defective it will trip much faster. If it's hot, the time before it trips during an inrush event will be shorter as well.

Is the run long? Lugs on everything *TIGHT*? How hot is the main CB when everything is running?

I'll have to check the numbers when I get home. I know for a fact that we were not messing with the thermostat at all when this happened (we have one of the programmable ones and we basically don't touch it other than to turn on/off the air).

Everything seems to be in order with the breaker itself. It's locked down tight, and it's not alarmingly warm or anything during the normal run of things. The run from the breaker to the A/C is probably 10 feet or so.

I do know that my A/C has like a 5 minute delay between on/off cycles. When I replaced the thermostat I had to wait a while for it to kick back on so I could test it. This was confirmed by my old neighbor who was an HVAC guy.


Yea, if I had a couple grand to throw around, then this wouldn't be a problem. I have plans to go up to 200 at some point (and probably put an additional 100 in the garage), but it's just not financially feasible right now. I'm looking for a cheaper solution.

Originally posted by: shilala
Replace the 100 amp breaker after you test the load across it.
My guess is that it's junk.
It happens.

Is there an easy way to test this? I have a meter and stuff, I'm just unaware how you would go about testing a breaker.

Originally posted by: skyking
Go tally up your breakers and compare to the main. Every house is 'oversold', so to speak. The sum total of breakers is greater than the main, so large but acceptable loads on every circuit will break the main. That said, I agree with shilala, (grudgingly :p) and think the OP should check the actual load when it trips. I suspect a bad main also.

Yup, the individual breakers add up to way more than the 100A total, which is why I would not be surprised if I actually was going over. The only times that it has happened this summer is if we are running the washer and dryer, a 27 and 36 inch TV, a fridge and a full size freezer, a PC (usually during a gaming session when it happens)... along with all the lights and other random stuff.

I know, I know, I could just limit my power usage (multiple TVs, PC, etc.)... but what fun is that?

I really just figured that it would be a matter of getting some kind of capacitor to buffer out the startup current on the compressor and that would be the end of it.