OK everyone. 1st time on Stack Exchange here and I’m looking for a few answers on wattage and not the simple stuff you should already know before going off half cocked buying a gen set. OK.

First.—- I have a generator that’s 12000 watts surge and 9,500 watts running. However the AVR is only good from 7kw-9kw plus the alternator/genhead has a sticker when disassembled that says 9.0kw. Now for the kicker.... if I didn’t tear it all down or load test it etc would an easier way be to find the 2 pole breaker on the generator and find the rated amps and multiply by 240volts?

If that’s the case my max (rated) output would only be 8,880 watts at 240 volts from my 37amp 120/240 volt 2 pole switch at the 50amp plug on my generator.

Am I wrong or can I just find the amperage of the 2 pole breaker and multiply that by 240 instead of hooking up my meter etc etc??? I’m just trying to find out the easiest way before buying. I’ll only be using a 9,000watt or more (running watts) with a 50 amp outlet to run my home off a interlock.

Ps does the same go for amps on the 2 separate push button breakers for 120/240 volt 50 amp outlets? I’d simply assume half the total on one 120 leg and half on the other 120 leg.... any help would be HUGE thanks guys n gals.

  • Can you get us a make and model for this genset of yours? Feb 24, 2020 at 4:36
  • Yes. 2019 Duromax XP12000EH. Which is made by Ducar as is pulsar, rainier etc etc. I have noticed other gensets in this catagory that have a 9,000 watt rating with 38amp 2 pole breakers. Which give it just over the 9kw mark... Feb 24, 2020 at 8:04
  • According to the manufacturer's web site, this is a 12,000 W (startup) with 9,500 W of continuous power capability. What what EXACTLY is your question? What you have written above is terribly confusing! Please consider rewriting it to be more clear about the situation and the problem you are having. Please leave out the editorial content as that doesn't help things at all.
    – jwh20
    Feb 24, 2020 at 12:49
  • Simply put my generator states wattages that the electronics cannot simply maintain in my eyes. The avr is rated to have 7kw to 9kw max, then the 2 pole 120/240volt breaker for the 50 amp plug/is only rated at a max of 37amps. Well 37amps at 240 volts adds up to only 8,880 watts correct? Yep. That in conjunction with an AVR of a max rating of 9kw kinda leads me to believe it’s not putting out 9500 watts as well my meter says the same thing. My question was simple can evaluate the true wattage of a generator by the max amps of the breaker it has. Feb 24, 2020 at 20:07
  • Not sure why the down vote as I had upvoted after going through a learning curve on small generators myself.
    – Ed Beal
    Feb 24, 2020 at 21:47

1 Answer 1


First no mater what the generator’s alternator has stamped on it this means nothing! You do not know the test conditions in either case for the alternator or the complete gen set. And taking things apart probably voided warranty.

I maintain very large gen sets and to provide an example one is a 350kva this gen set is certified for life safety equipment and I have loaded in one extreme case close to 500k it was not a life safety issue but we lost a secondary and we needed that amount of power 490a for close to an hour and the owner said to try it. It did fine.

I have small 5-8k gen sets that can maintain 25% overload conditions but these were designed for heavy duty use

My biggest home generator is similar to yours and I would not expect it to be able to pull more than full surge load any longer than ~15 seconds (the amount of time for most large fans to come to speed) why do I say this because the windings and slip rings are 1/2 the size of my smaller heavy duty models. Without knowing the testing that gen set was certified to it would be best to keep your loads to 80% of the values unless they are stated for use at 100%, my gen sets only the life safety ones are certified for 100% full load (3 + hour run time) with a 15 minute cool down after loading required.

Added per op comment: The breakers are inverse time and will allow more amperage to be drawn than there listing based on the curves for that brand. 50*240= 12000w the breaker will hold for a short time well beyond this value normally allow 3-5x for a short time.

code requires the wiring to be sized 125% for motor loads and continuous loads most home loads of any size are not continuous but let’s do a standard de rate of a 50 amp device .8 x 50 = 9000w that is close but all the loads that are non motor or don’t run for 3 hours or more are rated at 100% so real value is someplace will be in between 9-12kw

Code allows / requires the mfg values instructions to be used per NEC 110.3 in the U.S. as I have explained some alternators may have some value that may have a different capacity than what is stamped on it. My gen set also has additional 120 outlets to fully load my gen set the fine print shows these receptacles must be used on loads that are isolated from the main, are they cheating ? The total it can output meets specifications. Most of the small generators play this game.

This game is just like shop vacuums and air compressors. If you have either of these things that are not true commercial units don’t look two far or you will get really mad because they don’t even come close to the HP rating they advertise. The only way to know on your gen set is to use a load that is within the testing requirements of the generator and measure the output. I did this and following there requirements mine passed on a real 100kw testing system at my plant. But I had to have 12 amps on the 2 separate 120v receptacle sets. You can ask as I did for testing conditions (they even state sea level and 72 deg f temp and premium fuel (no methanol) the methanol in the fuel I was using was the difference well that and having to pull 12 amps on ea leg through the receptacles. So it may sound funny but it’s not what you see it’s how things are measured.

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    Btw I did not void any warranty... I own an automotive repair shop and had some work to do to it they authorized me to do with warranty intact. So we’re all set there. Feb 24, 2020 at 20:10

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