My new 17,500 watt portable generator

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  #1  
Old 06-22-14, 02:56 PM
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My new 17,500 watt portable generator

Hi Group,

I'm new to the forum. I recently purchased a new Generac 17,500 continuous watt portable generator. The unit can supply power at 240volt @ 72.9 amps. It's max surge capability is 109 amp or about 26,000 watts.

My plan is to back feed into my main panel. I have purchased the proper interlock for my panel.

Here is my question though. The generator is not designed to supply the entire 72 amps from a single source. It has a 50amp @ 240 volt outlet which supplies 12000 watts and a 30amp @ 240 volt outlet which supplies 7200 watts. There are also smaller outlets on the generator.

I would obviously like to make full use the best I can of the available power.

This is what I want to do. I want to install a 60amp breaker in my panel and back feed both the 50amp and the 30amp sockets to it in parallel.

At first I thought why not just put in a larger breaker than 60amps but then it occurred to me my panel would draw power evenly between the 50 amp and the 30amp so 60 amps is really all I can get with it in parallel before the 30amp blows.

Other than adding a sub-panel and wiring the 50 amp to one panel and the 30 amp to the sub panel, does my solution sound reasonable with interlock and a 60amp 240 volt breaker along with 2 generator outlets wired in parallel?

Thanks.
 
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  #2  
Old 06-22-14, 03:24 PM
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I don't think it is a good idea to double feed your panel from two outlets of the generator. You don't know if the outlets are wired in the proper phasing.

A better option is to have two generator panels with separate interlocks, and separate loads. One will be for the 50 amp feed, and other for the 30 amp feed. Keep the lighter loads in the 30 amp gen panel and the bigger ones in the 50 amp gen panel.
 
  #3  
Old 06-22-14, 03:56 PM
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Have you checked the actual load on your service? Turn on as much load as you can and check with a clamp on meter,you might be surprised how much load you really have.
Geo
 
  #4  
Old 06-22-14, 04:49 PM
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Though it consumes 16 gallons of gas every 10 hours of running at 50% load capacity it is much cheaper than a standby generator and with a power capacity of 17.500 watts of continuous output it can easily meet all your power requirements for the home.
Do you realize how much gas that is...... it would be almost 40 gallons a day at half load. You should be looking to reduce your load on the generator.
 
  #5  
Old 06-22-14, 05:13 PM
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I think few realize how much standby power actually costs vs commercial power.
 
  #6  
Old 06-22-14, 05:30 PM
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>>> I don't think it is a good idea to double feed your panel from two outlets of the generator. You don't know if the outlets are wired in the proper phasing.

When you say that, do you mean something like I don't know which wire is the "red" wire and which wire is the "black" wire on each of the generator outlets?
 
  #7  
Old 06-22-14, 06:28 PM
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All the receptacles are connected to four lines. I just highlighted them to show the setup. The red and black may not be what is actually used.

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  #8  
Old 06-22-14, 06:36 PM
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Right, so long as I keep everything in parallel though I should be good.
 
  #9  
Old 06-22-14, 07:19 PM
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No, you won't be good. The setup you propose is dangerous, and violates several code articles. If you want my honest advice, run from that generator. Either settle for a smaller unit (my 7550 goes through about a gallon an hour at full load), or get a liquid cooled propane/nat. gas or diesel model. While gas may be easy to get a hold of in a non-emergency, during a power outage everyone is scrambling for gas, and many stations run out. Add into account that gas is almost $4 per gallon and you will be using almost 40 gallons per day, that is going to get expensive real quick and you'll see why the standby system may just be cheaper in the long run. It also would be impractical to store that much gasoline, as it goes bad in about a month.

You really need to figure out how much power you actually need. I have spent many hours running every receptacle and lighting circuit, as well as the oil-fired boiler in my house on a 4,000W generator. When I used the 6,000W unit through Hurricane Sandy, I was able to run a few hundred lights for Halloween as well as a stove burner or two, or the washing machine.
 
  #10  
Old 06-22-14, 08:10 PM
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>>>No, you won't be good. The setup you propose is dangerous, and violates several code articles.

Please explain why?

The generator allows for both the 50amp 240 volt plug and the 30amp 240 volt plug to be connected at the same time.

Also, code allows for an interlock on the main panel.
 
  #11  
Old 06-22-14, 08:34 PM
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For one, conductors smaller than 1/0 cannot be paralleled. By running 2 cables into 1 panel, you'd be paralleling them. Also if one of them would become unplugged, the male prongs would be live.

Option 2 would be to feed 2 separate panels, but that wouldn't pass either because you can only have 1 feed to a structure. But that would be the lesser of risks.

Still, what makes you think you need a generator this big?
 
  #12  
Old 06-22-14, 08:52 PM
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I live in Florida. There was a time a few years ago where the power was out for nearly a month. 4 hurricanes had passed through the area.

I get that it's expensive. But there are no natural gas options on the street. If gasoline becomes non-attainable, I think there is a bigger problem that requires evacuation of the house for a variety of reasons.

I want to be able to run everything- air conditioning, washer/dryer, hot water tank, etc.. Granted not all at once, it can be carefully managed.

I've got an elderly mother in law also living in the house who would likely perish without AC.
 
  #13  
Old 06-22-14, 09:32 PM
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I live in Florida. There was a time a few years ago where the power was out for nearly a month. 4 hurricanes had passed through the area.
If that's the case, I wouldn't trust a little air-cooled engine running that long, especially the ones made for consumer grade generators. You also need to keep in mind service intervals with these, you need to change the oil, oil filter, and air filter every 100 hours.
 
  #14  
Old 06-23-14, 12:01 AM
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I'd be just running the 50amp to house main. Could use extension cords to run individual items, like the fridge or AC.
What your wanting to do, is run 60amps from a 50amp socket and a 30amp socket. If one line goes dead, you could be trying to pull 60amp from a 30amp socket. You'll end up popping the generator 30amp breaker. All lines have to be rated for 60amp (i.e. the power you want to draw).
In your case, I'd consider returning genny and getting one you can hardwire if possible. Your genny is really made for jobsite uses like construction. And they are louder...plus the fuel consumption noted. jmho
 
  #15  
Old 06-23-14, 06:45 AM
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As stated here just run off the 50 amp 120/240 outlet. If you have the interlock then that will supply both sides of your panel.

The 30amp outlet probably only uses one winding, and will severely unbalance the generator. Dont even attempt it..

There was a time a few years ago where the power was out for nearly a month.

How will you get fuel when all the gas pumps have no power???


To do what you want and be somewhat economical is propane units. Get say a 250 gallon propane tank and the smallest gen you can run.

I want to be able to run everything- air conditioning, washer/dryer, hot water tank, etc.. Granted not all at once, it can be carefully managed.

I've got an elderly mother in law also living in the house who would likely perish without AC.

Yes you have a window units on hand then. They will use far less amps then the central A/C. Or find out what size you need to start you central a/c which would be your biggest draw. Hot water heater ?

LP you can store....

If you have the $$$, this should run what you want.

Briggs & Stratton 40400 12kW Standby Generator System 200A Service Disconnect + AC Shedding

Or save money, run window A/C and just a few items...( Still need to be sure to have propane on hand...)

Powermate PM0135500 LPG Series - 5500 Watt Electric Start Portable LP Generator
 
  #16  
Old 06-24-14, 05:43 AM
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Here is what I am thinking. My interlock should be here this week. When I pull the panel cover off to install the interlock, I'm going to use that opportunity to measure amp draws.

I am going to use the 50amp plug to wire into my home panel as stated above. It will have to be enough, will have to manage the loads. If it's not, maybe I'll pull the water heater breaker out of the panel and put it into a subpanel with a transfer switch and connect that to the 30amp plug.
 
  #17  
Old 07-09-14, 08:38 AM
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A licensed electrician in my area installed the same genny for a customer. What he did was backfeed the main panel from the 50 amp recepticle and installed a sub panel to distribute power from the 30 amp recepticle. Not sure how he seperated the main and sub while using the genny, but it did pass inspection. Interlocks are legal here.
 
  #18  
Old 07-09-14, 03:54 PM
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What they did was backfeed the main panel (or install a whole-house transfer switch upstream of the main panel). This was connected to one half of the generator's power (one generator receptacle). Then they installed a transfer switch (same make and model would work) in the line from main panel to a subpanel for the other half of the generator's power via another generator receptacle.

Usage:

Main transfer switch or backfeed set to generator, subordinate transfer switch set to utility: Generator delivers its power to house including subpanel via main panel only. Limited by breaker on generator receptacle being used, to about half of the generator output.

Main transfer switch or backfeed set to utility, subordinate transfer switch set to generator: Generator delivers its power to subpanel only, main panel gets utility power or is dead. Limited by breaker on generator receptacle being used, about half of the generator output.

Main transfer switch or backfeed set to generator, subordinate transfer switch set to generator: Generator delivers up to half of its power to house excluding subpanel, delivers up to half of its power to subpanel. Limited by breaker ratings on generator receptacles and also limited by total generator output.

Your water heater, as you mentioned, would be a good candidate to segregate and use a separate generator receptacle for. Its original 30 amp breaker would remain in the main panel for when utility power is being used. With just the water heater on that branch and a cord with 30 amp plug for the generator hanging from the wall mounted transfer switch, no additional breaker is needed next to the water heater.

********

Do not take the outputs of two separately breakered circuits or receptacles and combine them to provide a greater amount of power for something.

Does the generator have lug terminals (perhaps behind a small cover) intended to bypass the receptacles and allow connecting up the entire output to one destination such as your house panel? This might be mentioned in the instructions.

Usually, a larger generator will consume more fuel powering a relatively small load compared with a smaller generator power that same load.
 

Last edited by AllanJ; 07-09-14 at 04:55 PM.
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