Window air conditioners and circuit breakers

Okay, it’s hot. We have an old window a/c unit that is in charge of cooling our downstairs. It’s loud but it gets the job done.

Today, though, the circuitbreaker on that circuit has tripped 4 times. Each time I’ve tromped to the basement and reset it, but now I’m wondering.

The breaker covers the dining room, which is where the unit is located, and the basement. Other than the a/c and a light, which is off, nothing is plugged in or used in the dining room. The hot water heater and the furnace are the only appliances in the basement.

Is this most likely a utilities issue in some way? (I’m sure electricity use is very high today.) A circuit issue? (We’ve never had trouble with it before, but who knows…) An a/c issue? (Is it finally on its very last legs?) Is there any potential harm in resetting the breaker time after time?

Any thoughts appreciated. Many thanks.

I would think that your A.C. is developing a problem, unless there is something new plugged into that circuit you’re not thinking of.

Could be there is something on the breaker you’re not aware of.
Could be the AC is drawing to much current.
Could be the breaker is bad.

It is highly unlikely it has anything to do with the utility

Yes it it is bad for the breaker to keep being tripped, eventually it’s going to fail completely. Usually they just stop working sometimes the internal arcing will burn it up and melt the breaker.

The best way to troubleshoot it would be to put an amprobe on at the breaker inside the panel, but I don’t recommend most people opening their panels.

As a general rule, I suggest to people not to reset a breaker more than twice without figuring out what the actual problem is.

The air conditioner is on the same circuit as the water heater? An electric water heater? That might be a simple overload right there.

It could be a utility issue or your AC compressor is starting to go out.

If it’s your AC and it’s a window unit you may do better by replacing it instead of repairing it. Sometimes an AC tech can add a hard start kit to a central AC unit. The hard start kit is essentially a capacitor which boosts the voltage at the compressor and allows it to draw more power with less current. I don’t know if they make kits for portable AC units.

Your utility has a target voltage of 125 V(USA) which they want to maintain at your house. However the voltage drops on your distribution line as the power needs along that line increase. During high use periods the voltage may suffer for those customers towards the end of the line.

Some of these lines have voltage regulators on the line to help boost the voltage and they work great except during very hot periods these voltage regulators could overwhelmed and are then set lower.

I used to work for a utility and during heat waves some of our voltage regulators had to be adjusted back (instead of boosting 8% voltage they could only boost 5%) or risk overheating and failing.

So it could be that the latest heatwave has caused your utility co to place some voltage regulators into emergency mode which hs dropped the voltage to your house.

Lower voltage means that your AC unit has to draw more current to get the power it needs. Current causes the breaker to trip.

A voltage meter would tell you if your house voltage is suffering. If it’s low without the AC unit on then blame the utility. If it’s 115 or higher then your AC unit is probably going to fail soon and the tripped breaker is your first warning.

Thanks for the responses thus far. Definitely useful! I doubt I’ll try to get the unit repaired if it’s on the brink–it doesn’t owe us anything. The idea of a voltage meter is a good one.

Sorry, should have specified. It’s a gas water heater.

Start by reading the name plate of your AC unit. If it is high like 15 amps then your breaker had better be in good condition, and not have much added to the circuit. But if it is in the 10 or less range then it will take more investigating.

volt meter the outlet. And if you can safely take an amp reading of the circuit and the AC.

It could be a combination of things. I think if the A/C has lost Freon, it would have to run longer, but draw less power. If the windings are getting old and leaking electricity, that could be the problem. If the incoming voltage is low, it will draw more amps at the same load. finally, circuit breaker can get old and open at less than rated power. The more often they trip, the less power it takes to trip.

If the A/C unit is very old, you might be able to buy a newer one with the same BTU rating that would be a little more efficient and draw enough less power to keep the breaker from tripping.

Add to this…

If you have low voltage it will put a strain on (read damage) household appliances.
Feel the cord while it’s running to see if it’s hot.

Electric utilities often respond to overloads by temporarily dropping the voltage delivered, a ‘brownout’. Loads like light bulbs just burn a bit dimmer, or ‘browner’. But things like AC’s have to draw more current to get the same amount of power, and that increase in current draw can trip your circuit breaker.

But if it does, you were near the limit of the breaker anyway. You ought to have a separate, 20-Amp circuit for an air conditioner.

By the way, for continuous use derate circuts to 80%, a 15 amp breaker and 14 gauge wire shouldn’t have more than a continuous 12 amp load.

It’s not a dedicated circuit, so that restrictions not applicable.

The most likely cause is a clogged condenser coil (the outside one), particularly since you say the unit is loud.

With the unit running, go outside and put your hand near (but not on!) the condenser coil. Do you feel a good amount of warm air moving past your hand? Carefully move your hand closer to the coil and if it isn’t burning hot, touch it. [I’ve had cases where people got burns from touching the coils, which is why I don’t advise touching it right away.]

The coil should be warm or hot to the touch, but not so hot that you can’t hold onto it. There should be a sizable quantity of air moving through the coil which you should also be able to feel.

If the coil is excessively hot and/or you can’t feel much (any) airflow, you probably need the coil cleaned. I do this with an air compressor and a set of wands (lets me reach high-up units). If you can get a professional to clean it for you, I’d suggest that.

If you decide to try cleaning it yourself, switch the unit to “fan only” mode and let the coil cool down before cleaning it. Hitting a hot coil with cold water from a hose is NOT recommended. Be careful to not bend the fins on the coils - they are quite fragile, and will cost you more to get straightened (with a gizmo called a “coil comb”) than the unit is worth.

Hopefully cleaning it will get you past the current heat wave - you don’t want to have to buy a unit when everyone else has already flocked to the stores and bought all the better units, leaving the low-quality ones with poor EER’s and short warranties.

Did you mean to say a “continuous use” or “high capacity factor” circuit?

Because whether or not the circuit is dedicated to one appliance has no bearing on taking precautions for a situation where it has a continuous current flowing through it. In fact a circuit which has a high capacity factor load and other sporadic loads (ie a non dedicated circuit) is exactly why you should derate the line.

No I meant what I said. The 80% limitation is a specific code restriction. It doesn’t apply in this situation because it is a convenience outlet in use.

If you want to argue it’s a best practice or whatever your welcome to but it’s not a NEC value.

15 amps on a 15 amp circuit is already a very conservative safety margin. Tacking on other arbitrary restrictions is really unnecessary.

Lots of good stuff here; thanks to all who chimed in.

Just to follow up: For a variety of reasons, mainly the age of the original unit, we decided to replace it with something newer and more efficient. Despite the heat wave, we got a reasonably good deal from a local store, and so far so good: quieter, cooler, and generally better. Didn’t have a new a/c unit in the budget, but so it goes–

Thanks again.

Just wanted to comment that we were seeing similar behavior in our apartment recently. With our (Energy Star rated, 6500BTU) A/C and the TV on the same circuit, it was tripping 4+ times daily. My wireless router and stereo receiver were also on the same circuit, and were both resetting multiple times daily.

After a brief power outage, everything is now working perfectly even though it’s gotten hotter. Have to believe it was a utility issue.

That’s not a good idea. When the heavy motor in the A/C kicks in, there will be a heavy spike put onto that circuit. Spikes like that aren’t good for electronic equipment, like TV’s, stereos, and routers. Most modern ones have circuitry to prevent actual damage from those spikes, but they can still cause them to reset. Like you have been experiencing.

Much better to have the A/C on a separate circuit. If you can’t do that in your apartment, consider running a heavy extension cord from another outlet circuit to power your electronics, and leave only the A/C on the current circuit. (But don’t use an extension cord for the A/C!)

Slight hijack, but US power should be between 115 and 120VAC to be in spec. 117 is the target. 125 would noticeably reduce incandescent bulb life.

On topic: Refrigeration compressors typically fail due to shorted motor windings. In the early stages the short often is only there when the motor gets hot, and clears when it cools. A window unit is so close to the breaker rating that the breaker will trip before the shorted wire burns through, so you get what the OP is seeing.

It may be a tired breaker of course. The OP should replace the breaker, and if a new breaker trips, then the AC should be replaced or retired before resetting the breaker even once. If the old breaker has tripped a few dozen times it may be getting tired even if it wasn’t to start with. A replacement AC unit may be tricky to source this time of year.

[/more hijack]
Standard voltage is 120V and many regulations require operating voltage ± 8 volts. Which gives a range of 112-128. Guess which end of that range gives the utility a little more money? Motor loads will draw higher current at low voltage but the total power they draw stays about the same. On the other hand passive loads like lighting will draw constant current but use more power at higher voltages. So your friendly utility would much rather provide a “legal” 125V to your home and get a few more pennies from each of their 1 million customers.

Notice in my post I said that the UTILITY uses 125 as a target. Not talking about NEC but business practice. Those voltage regulators that I discussed in my first post are set to provide 125V on the load side of the distribution transformer.

Yes, it shortens the life of the average light bulb but the light burns a little brighter and the utility doesn’t have to buy the replacement. :smiley: