House A/C problem due to breaker

[rbstern]

Hoping to get a little feedback on what I experienced on Saturday.

Noticed the A/C wasn't cooling the house. Checked outside, the fan on the outside compressor unit wasn't spinning. The 30 amp breaker for the outside unit was tripped. I reset it and the fan came on a moment later. Didn't think much of it. We had a 30 minutes power outage the day before due to a bad storm, figured it must have tripped the breaker when the power went. A short while later, the house wasn't getting cooler. Checked the outside unit again. Again, fan not running. Again, breaker tripped. Reset it two more times, only to have it trip within 10 minutes each time.

It occured to me the breaker might be bad. The last time I reset it, I noticed an arcing flash. Looked at the panel. Had one other, identical 30A breaker in the panel for the dryer. Turned off the power, removed the 30A for the A/C, swapped the dryer breaker. Everything turned on normally. And stayed on. So, bad breaker, apparently.

After the power was back on, I had a chance to look at the bad breaker. Some fairly heavy carbon on the terminals. The A/C wire is stranded aluminum, and it had some anti-oxidizing goop on it, as it should. Hard to tell how well coated it was, but I though (by flashlight), the aluminum wire had some carbonizing on it as well. Set out to Home Depot to get a replacement breaker (QO type...$35...argh!) and some of anti-oxidant goop.

With the power off again, I undid the A/C breaker, carefully cleaned the end of the aluminum wire with sandpaper, coated the wire ends and inside the breaker terminals with the anti-ox goop, reattached the wires, removed any excess goop, and reinstalled the breaker. Installed the replacement breaker for the dryer circuit. Everything powered back up as expected and all has run well since.

Wondering: Was it a poor install job on that aluminum wiring that led to the carbonizing and tripping? Was the breaker just deteroirating? Any insight appreciated. In case it matters: The house is about 4 years old, and this is all original equipment from the build.

 

[grsthegreat]

Breakers do go bad. However usually when theres carbon buildup its due to wires not being tight on breaker. Aluminum wires are supposed to be torqued per spec on panel. Otherwise , if it were me, i would check tightness under every aluminum wire connection. Same contractor may not of tightened any of them.

loose wire causes arcing. Arcing creates carbon and heat. Heat trips breaker thermals.

 

[Tinhack]

The start capacitor(s) in the outside unit is probably bad. My unit has two. One for the compressor and one for the fan motor. I've replaced the fan capacitor twice and the compressor cap once in the last 10 years. If you don't do electric, have it serviced. That cabinet has 240 volts inside.

 

[CJONE]

Test the start cap as tinhack said it is [possibly] bad but normally once they fail they are dead. My guess is the POS aluminum wire loosened up and caused a voltage drop requiring more amps to start the unit. I don't care what anyone says aluminum wire sucks! I personally have seen it burn down 2 homes so far. This is why they quite using it for branch circuits. Dicharge cap before testing it!!! If you have aluminum wire anywhere check the tightness of it every few years and more often where vibration is present. EG air conditioner. Or replace it with copper if that is a option. CJ

 

[JPRambo]

Aluminum wire expands when it get hot. But it can't expand where there is resistance. And when it cools it shrinks. So it gets hot expands and cools moving away from the lug or screw that was tight against it. Over time the connections screw needs to be re-tightened. This could have caused the sparks you saw. Breakers trip because of the heat build up within them. Heat is produced by power (voltage x amperage). Excess power is caused by a loose connection (sparks).

 

[nickfank]

Wondering: Was it a poor install job on that aluminum wiring that led to the carbonizing and tripping? Was the breaker just deteroirating? Any insight appreciated. In case it matters: The house is about 4 years old, and this is all original equipment from the build.

Since the house is so new, I wonder if your breaker was an arc-fault breaker?

I wouldn't expect a loose connection & heat on the *outside* of your breaker to cause the bimetal on the *inside* to heat up enough to trip. However, many jurisdictions now require arc-fault breakers, and it sure sounds like you had an arc on the connections.

 

[rbstern]

Since the house is so new, I wonder if your breaker was an arc-fault breaker?

I wouldn't expect a loose connection & heat on the *outside* of your breaker to cause the bimetal on the *inside* to heat up enough to trip. However, many jurisdictions now require arc-fault breakers, and it sure sounds like you had an arc on the connections.

It's one of a handful of non-arc fault breakers in the panel (along with the dryer, septic pump, furnace blowers). All of the living areas have the code-required arc fault breakers. Don't know if the code has changed, but when built in 2018, circuits serving non-living spaces could still be the traditional breakers without the arc fault feature. We had a lot of trouble with one of the arc-fault circuits during move-in. Electrician had to come back five times to fix a circuit that wouldn't behave. Finally traced it back to a kink in a wire.

 

[rbstern]

Good tips, everyone. Going to make a list of any circuits in the panel that have aluminum wire, and make checking the terminals an annual maintenance item. The A/C may be the only circuit with aluminum, but I'll have to look closely to be sure. The dryer 30A is copper. I know the septic pump 20A is copper. I added a 20A 240 for my table saw, and that's copper.

 

[2manyrocks]

How tight were the connections to the breaker? Did you check the tightness of the connections at the AC? It may have been a bad breaker or it may be something caused the breaker to repeatedly open and go bad. Maybe it was just the connection at the breaker that was the problem. Maybe something else is loose or corroded in that circuit. With this being aluminum, suggest you take a moment to check all of the connections, obviously verifying that the power is off.

 

[Chewwy]

Good tips, everyone. Going to make a list of any circuits in the panel that have aluminum wire, and make checking the terminals an annual maintenance item. The A/C may be the only circuit with aluminum, but I'll have to look closely to be sure. The dryer 30A is copper. I know the septic pump 20A is copper. I added a 20A 240 for my table saw, and that's copper.

There are many opinions and recommendations regarding dealing with aluminum wiring most of them conflict with each other. I am aware of no where that recommends annual maintenance.

 

[kenmac]

Just an FYI ....These are Run capacitors. Not start capacitors

 

[grsthegreat]

Test the start cap as tinhack said it is [possibly] bad but normally once they fail they are dead. My guess is the POS aluminum wire loosened up and caused a voltage drop requiring more amps to start the unit. I don't care what anyone says aluminum wire sucks! I personally have seen it burn down 2 homes so far. This is why they quite using it for branch circuits. Dicharge cap before testing it!!! If you have aluminum wire anywhere check the tightness of it every few years and more often where vibration is present. EG air conditioner. Or replace it with copper if that is a option. CJ

They have NOT discontinued making aluminum wire for branch circuits. They only discontinued it for 15-20 amp circuits. You can still use it on larger branch circuits. Todays alum wires are nothing like those of old.

we use it all the time. Also, all the power lines overhead are aluminum. It works great as long as its installed properly.

 

[rbstern]

They have NOT discontinued making aluminum wire for branch circuits. They only discontinued it for 15-30 anp circuits. You can still use it on larger branch circuits. Todays alum wires are nothing like those of old.

we use it all the time. Also, all the power lines overhead are aluminum. It works great as long as its installed properly.

Comment / question: This is a 30A circuit, 240v, for direct wire appliance (HVAC compressor). And the aluminum wire is stranded, which I believe is standard for these types of instances. So, I assume the 30A you are referring to would be direct wire to an outlet like a dryer. Is a drier outlet considered a branch circuit? The dryer circuit with the 30A breaker in the box had solid copper.

I know, in my previous house, built in 1992, there was stranded aluminum wire used for a 40A (or maybe 50?) electric range.

 

[grsthegreat]

while you could run a 6/2 aluminum ser cable for a 30 amp ac unit ( as i recall thats the smallest aluminum romex style wire available - listed SER cable)very few people do. Until the craziness in prices kicked in a year and a half back, 10/2 copper was relatively cheap And inline with the cost of 6/2 Aluminum. Last week i paid nearly $400 for a 250 foot roll of 10/2 romex. I expect to see more aluminum runs out there soon.

ps: i edited my last post. That was supposed to say 15&20 amp circuits…not 30. Fat fingers.

 

[rbstern]

while you could run a 6/2 aluminum ser cable for a 30 amp ac unit ( as i recall thats the smallest aluminum romex style wire available )very few people do. Until the craziness in prices kicked in a year and a half back, 10/2 copper was relatively cheap And inline with the cost of 6/2 Aluminum. Last week i paid nearly $400 for a 250 foot roll of 10/2 romex. I expect to see more aluminum runs out there soon.

ps: i edited my last post. That was supposed to say 15&20 amp circuits…not 30. Fat fingers.

Got it. Thanks for clarifying on the 30A.

 

[grsthegreat]

Personally i just think the connections were loose. Do you recall if the screws on old breaker were tight? Should need quite alot of pressure to loosen.

 

[rbstern]

Personally i just think the connections were loose. Do you recall if the screws on old breaker were tight? Should need quite alot of pressure to loosen.

Two issues: Was working in poor lighting, and didn't have ideal tools at end (screwdriver blade was a bit too small). But, I do have the impression the carbon on the terminals made turning the screws harder, in either direction.

When I turned off the power to put the new replacement breaker in for the dryer, I was sure to have better lighting on hand (headlamp), and more appropriately sized tools. Made sure the screws in both circuits were firmly in place. I'll recheck the next time I happen to have business in the box.

 

[kenmac]

there are many homes where alum wire is run to A/C condensers.
Size of alum depends on the run and the circuit / load requirements.

 

[Tinhack]

I wouldn't use aluminum wire for anything--Even if the wire was free!

I remember back in the 80's when some builders started using aluminum wire. Many of the new homes burned to the ground. GM started using it in autos for the wire that runs to the rear of the vehicle. It was failing there too. If there's any chance of movement or vibration, it's going to fail. Typically with catastrophic results.

 

[jaxs]

Breakers do go bad. However usually when theres carbon buildup its due to wires not being tight on breaker. Aluminum wires are supposed to be torqued per spec on panel. Otherwise , if it were me, i would check tightness under every aluminum wire connection. Same contractor may not of tightened any of them.

loose wire causes arcing. Arcing creates carbon and heat. Heat trips breaker thermals.

Instead of trying to point out posts with varying amounts of poor information, I'll just say imo everything the above quoted poster said in his posts is correct. I cringe at the sight of electric questions due to the number that always respond with poor information. I commend op for the common sense approach to fixing the problem then seeking affirmation. I believe his actions are those of one who understands more than the average but is and will remain a student reaching for perfection.