Hey Electrical Guru's - Got a Generator and running A/C question

Scotty Dive · Sep 19, 2012

I have been doing a bit of prep work identifying what each breaker in my panel controls in the house - After 40 years and a couple of additions, it was a great project to undertake and identified some interesting things which I needed to know and would have never guessed otherwise). Now I have a master list of what is what and will re label my breaker box so that it's up to date.

The next thing I did was identify all of the appliances etc I have and calculate the amps and wattage including surge needed to run those and what breakers they are on. So, when I have a power outage and I throw the main, turn on the breaker for the generator I am able to turn on only the breakers I need. I know what wattage my generator can produce - 7000 watts continuous and 8750 surge at 220v 30 amps. Here is my question....

The generator breaker in the panel is a 30 amp and my Generac generator runs 7000 continuous to 8750 watts surge. My A/C has a 40 amp breaker and needs 6400 watts continuous and 7000 watts surge. If I have NOTHING else running is it possible and ADVISABLE to run the A/C if needed? The wattage needed by the A/C is within parameters but the amps rated on the breakers are not matched. I know we can live without A/C but if it's possible to run and not going to cause any harm, I thought it might come in handy at night when sleeping.

edlegault · Sep 19, 2012

No. Figure a breaker is only good for 80% of its rating, i.e., a 30 amp breaker is good for 24 amps continuous. The 40 amp breaker on the AC is good for 32 amps. You would be popping the 30 amp breaker intermittently.

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dusty3030 · Sep 19, 2012

You can always try, or now is the time to get one of the on sale end of season 110v window units for 100 bucks or so. Just for emergencies.
That is how I have avoided buying a bigger generator. A cheap 110 window unit to slap in the back bedroom window and we all three camp out together if it's hot.
Winter we are fine because the forced air furnace is well within our output on my current rig.

BobRip · Sep 19, 2012

Only 7000 watts surge sounds way to low for an AC unit that runs at 6400 watts continuous. Only if it is an inverter AC would I expect that. Where did you get the surge number? Is it an inverter (variable speed compressor) AC.

Steave · Sep 20, 2012

Scotty Dive said:
Here is my question....

The generator breaker in the panel is a 30 amp and my Generac generator runs 7000 continuous to 8750 watts surge. My A/C has a 40 amp breaker and needs 6400 watts continuous and 7000 If I have NOTHING else running is it possible and ADVISABLE to run the A/C if needed? The wattage needed by the A/C is within parameters but the amps rated on the breakers are not matched. I know we can live without A/C but if it痴 possible to run and not going to cause any harm, I thought it might come in handy at night when sleeping.

If your AC requires 6400 watts to operate then your genny would never get it started. 6400 watts is somewhere close to 30 amps at 220 volts, it takes about 3 times that 30 amps to start the compressor. Even though its only for a second or two trying to start, your genny probably won't do it. As soon as the AC tries to start the genny will bog and there goes your 8750 watt surge rating.

Keep in mine that high end generators can be had for a premium that are well regulated and designed for induction loads such as motors and AC's but most are 3 phase and very expensive.

Dusty3030 has a good idea about the window unit.