# Rewire generator output



## Art Ramirez

Ladies and Gentlemen: 

I have an older Generac 17,500 watt portable generator which I want to use as standby/backup hardwired into my electrical panel. 

Can the generator be rewired to by pass its outlet panel and provide one set of leads that will provide full generator output to be hardwired into the house panel?

Thanks

Art


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## thehandyman1957

17,500 watts? Are you sure? That's huge for a portable gen set. As for your question, we would need to have a model # at the least and a make name.


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## exmar

Agree with Handyman, maybe 7,500Watts? Check to see if it has a 120/208 connector on the panel, simply plug in a cord. In fact, look a couple of posts down, titled, "120 feed to a 240 volt panel" and there is a whole discussion on doing that.


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## Art Ramirez

ok,

Here are some pictures showing the info requested.

Thanks

Art


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## Art Ramirez

exmar said:


> Agree with Handyman, maybe 7,500Watts? Check to see if it has a 120/208 connector on the panel, simply plug in a cord. In fact, look a couple of posts down, titled, "120 feed to a 240 volt panel" and there is a whole discussion on doing that.


Just posted pictures


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## thehandyman1957

Wow, and a Generac too, man that's nice. 

Does it run good? Man I sure wouldn't want to have to pick that thing up.....

I do see in the front panel pic that it shows a double pole 50 amp breaker and you also have two separate 30 amp 120 plugs. I would bet my ham sandwich that those are both on separate legs and that all power from the gen is coming through that 50 amp breaker. I would assume that the 220 twist lock is actually 30 amps per leg because of the reset breakers on the right. If so, you just need a good heavy duty cord. Be careful of your run lengths, Usually anything over 20 feet and your going to need a good 6/4 wire to carry that kind of ampage.


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## exmar

I sit corrected.  That is a beast! What's the noise level when it's running? Fuel consumption? Do you need 17.5KW for emergency use? I suppose you could do a "siamese" connection with two 30A plugs feeding #6 wire and then into a 60A breaker in your load center, that would give you about 13KW with no rewiring of the generator end. I'd get a diagram from Generac to make sure that would work before doing it though. If you rewire and then hardwire the genset in, obviously it won't be portable anymore. Looks like a 2006, so it's 11 years old, if you chat with Generac about the diagram, you might see what parts are still available for it before you spend $$ hardwiring it in. ( I recently found out from Ford that parts for new vehicles are only required to be available for 7 years, some of them only 5. $40,000 for a pickup and that's the support?) 


Handyman makes an interesting point, the 50A breaker is probably the "main" so, even though the nameplate says "72.9A" it's feeding through a 50A breaker. Generac is infamous for not overstating, but creatively stating the ratings on their gensets. e.g. "17.5KW genset, but feeding through a 50A breaker, that's only about 11KW, however the generator end can produce 17.5. Another reason to get the diagram and see what's what. 


Do you have any history on this as in what was it originally used for? 


I'd still get the disconnect and whatever size breaker you ultimately decide on to feed your load center. Connecting to the genset could be as simple as the siamese connection I mentioned earlier or two Weather proof 30A boxes with two sets of cables and connectors with the tie to #6 afterwards, cables, boxes and plugs would be expensive though.


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## thehandyman1957

Actually, it's not as big as I thought, Check it out. Not as loud as I thought either.





Ok, perhaps it's louder than it lead on. Here is another shot at it.
What I find very interesting is that the generator in this video 
is only 15,000 watts and it has the 50 amp 220 RV plug.
Where on yours, it's the 220 30 amp twist only. 
Leads me to believe I might be wrong about the 30 amps per leg idea. Hmmmm


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## thehandyman1957

Ok, so I found a wiring diagram for the same model but with the 50 amp 220 plug. And my original thought was correct. If you look at the 30 amp resettable breakers they are each feeding one leg each in the twist lock 30 amp plug. The whole thing is being fed through the 50 amp double pole breaker. So like Exmar noted, that's only 11kw for every plug on your generator. Tricky baby : (

Noted, that your reset breakers are in different locations but they accomplish the same thing. The two 30 amp reset breakers on the left I would assume are for the 30 amp twist lock and the ones on the right are for the 110 30 amp plugs, but I could be wrong. Some simple volt testing would tell you.

Oh, and it looks like I get to keep my ham sandwich : ) Both 30 amp plugs are on separate legs.....


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## exmar

Typical Generac, 17.5KW with only 11KW available, if it's 17.5KW, could be like HP ratings in small engines.  Another of their "marketing ploys" is a lot of their gensets are advertised as having 120V 20A outlets, (look at the outlets in your kitchen), and they are. However, they're usually fed from a a 15A breaker, "truth in advertising." 


That being said, I have two Generacs and have found them to be very reliable machines.


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## Art Ramirez

Been looking at electrical diagrams and I am dizzy. Actually the 17,500 gen does have a 50 amp plug - its on the bottom edge of the panel, directly below the 50 amp breaker. Also found the owner's manual and it has electrical diagrams -- pdfstream.manualsonline.com/0/0d424a00-c9e5-459d-b935-e715350151da.pdf -- to me, it appears that line 11 and 14 are the hot lines coming out of the generator and feed all plugs after going thru the proper circuit breakers. 

So my question still stands - could I connect into those two wires bypassing all plugs, go thru a 70 amp breaker and connect to my building panel. in this manner I can get the full use of the generator's cap.

BTW - also own the 15000 unit which is connected thru the 50 amp plug. It has been used once for about 10 hours due to winter time power loss --- have you ever tried to unroll a 50 amp plug in cable in 18 degree temp.

We have a small business which requires refrigeration, we currently have 2 walk in freezers and 2 walk in coolers and will be adding one of each by end of summer.


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## Handyhiker

From the diagram posted you are correct. These two wires do feed all outlets as the power wires. So yes you could feed a single outlet from these wires. I do not know what the actuall output of the generator is but this would let you use all available power. 
What wire size feeds the 50 amp breaker?
So 11 and 44 are power and 22 is neutral according to the diagram. 
I do not see a continuous rating for the generator on the ID tag. Is it possible that the rating is surge watts and not running watts? That may explain the 50 amp breaker. It may be a time delay to let motors kick in up to the 17.5 K then 50 amp max run.


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## Osviur

Hi,

This info comes from the 17500W Generac generator page:

The GP17500 is rated for a continuous output of 17,500 watts, with a rated amperage of 72.9 amps at 240 volts, and a maximum (surge) amperage of 109.4 amps at 240 volts. This rating is when utilizing both the duplex style and the twist lock style receptacles. The 50 amp receptacle, which is located on the underside of the control panel, will provide a maximum output of 12,000 running watts. Generac does not currently offer a portable generator capable of producing 17500 watts from one single receptacle. Allowing the rated load to be dispersed between multiple receptacles assists in preventing overloading of the generator, which could cause permanent irreparable damage to the generator. If a generator that is capable of providing the full rated wattage and amperage to a transfer switch is required, we would recommend considering our automatic standby generators. Further information on the automatic standby generators can be located here: Generac Home Generators | Backup power for your home | Generac Power Systems.... 

FYI


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## thehandyman1957

(Allowing the rated load to be dispersed between multiple receptacles assists in preventing overloading of the generator, which could cause permanent irreparable damage to the generator.)

That is a very interesting way of saying the generator may not be able to do what they say it should do. And by dispersing the load throughout all the receptacles, the chance of every item plugged in being turned on at the same time is much less, and thus not asking the required amount of surge power all at once. That is, the surge amount we put on the label (wink, wink, nudge, nudge).

The real tale teller of what they truly expected this generator to be able to do is the 50 amp breaker. Since everything is being run through it, there is simply no way you would ever get the quoted amount of power from this unit. 

What would be interesting is if you did bypass the 50 amp breaker and ran the leads to a bigger transfer switch, if it could indeed actually power as much as they state it will. I bet it won't. Thus the double speak about looking for a bigger stand by unit if you actually need that much power. 

Like I said, Tricky baby : ( 

I really like Generac but this is on the verge of false advertisement. This reminds me of the car stereo days when a car amp would state 1000 watts mono bridged and when you look at the inside you find out it can't even handle 50 watts RMS.


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## exmar

Sounds like you guys got it under control. I also really like Generac, but doubt you can pull 17KW out of the unit. At least for very long. I still think you should, at a minimum, get an interlock for the main load center breaker. Being conservative, after you have it connected, I'd do a test for an hour or three to see what it can actually do. Better to find out then than in an outage when you have full reefers.


Just realized that other than Generac, I don't know a lot about the ....less expensive....gensets. I've worked on a few engines, but never got into ratings or anything like this post required. Wonder if Generac is just following the industry in creative advertising. 


Good luck


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## Handyhiker

That really doesn't make much sence. If they expect you to have to use multiple outlets to get max power but still only have a 50 amp breaker for all outlets then the 17.5 rating for continuous power is useless. 

Guess that is why I like the old stuff, Onan, Kohler and others. My 12.5 Onan, heck all my Onans will pull more then rated watts and be happy doing it. I do know that old Kohlers will do the same. My newer Champions will almost pull rated watts but I do not depend on them to do so. 
I really don't know about other new generators pulling full rated output but I bet that many would struggle to do so. 
I think that an industrial rated set may be more likely to pull rated output then regular consumer style no matter who makes it.


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## exmar

FWIW a few years ago we had a...."inland hurricane"....I think they called it, power was out for six days here. A lot of folks were running gensets 12-14 hours per day to keep frig and freezers happy, actually I do that too. Anyway, the "less expensive" gensets that were run at or near rated power died quickly. I've heard and actually read here that running cheap units at max or rated power causes early failure. With our entire economy being drive by price point I suppose it makes sense. I've noticed in other things, it's getting harder to pay more for a quality item, there's the down and dirty, some stuff in the middle that's hard to get reviews or info on and the top of the line, e.g. Honda in gensets.


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## Osviur

Hi,

If you look carefully at the diagram, at the left side there are two input lines (11,44), coming from the alternator,that are connected at the upper terminals of the 50A CB. From this point starts two lines to the 120 V 30 A outlets AND feed the 50 A CB in a parallel connection.

The 50 A CB feeds only the 240 V outlet . This connector has the max capacity at a low price as stated in the same Generac page. An industrial connector as a 360R6W 60 A 3 lines is several times more expensive.

Generac states 17500 running watts (72.9 A PF =1) .

Loading the 50 A at a 90%, gives 45 A
Loading 2 x 30 A at a 90%, gives 27 A at 240 V (2x120 V)

Adding 45 A + 27 A = 72 A.


I hope this help to clarify this interesting topic. 

Regards


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## thehandyman1957

Ahh yes, you are correct. I did miss that. But my question at this point is, where is his 50 amp plug? His picture shows the 60 amp twist and the 2 30 amp plugs and the regular plugs but no 50 amp plug. Did they relocate it somewhere else on the generator? The version in the video I posted has the 50 amp plug right next to the 60 amp twist.


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## Osviur

Hello,

In this page:
https://www.partstree.com/parts/gen...-4486930-4487329-2006/control-panel-0g0727-b/

I found the 50 A connector, is the item # 12 and it is located underneath of the control panel, pointing downwards.

The original post by Mr Ramirez, asked for rewiring the generator output to get its full power delivered through a set of leads (3 wires).

In this generator, as stated in the plate, the maximum power is 17500 W at 240 (120+120) volts, 72 A.
Assuming a max permisible voltage drop of 5%, we will have a max drop of 12 V at full power-

Ohm's law: R = V/I , where V is the voltage drop and I the max current in Amp.

Let's say that the max current be 70 A, then;
12V / 70A = 0.1714 ohms.
This is the max resistance permitted to get, at full load, 240-12 = 228 V

To select the correct type of conductors there are several factors: current capacity, resistance, insulation type, number of conductors, how it is installed etc.

In this case the most important factors are the current capacity and the resistance. It si possible to determine this factor in tables like this one:

Wire Gauges - Current Ratings

As we will be using 3 lines (120-Neutral-120) we select that column, in the current line select 70 A, this gives a # 4 AWG cable. In the resistance column we find 0.24 ohms per 1000 feet.
We calculated a max resistance of 0.1714 ohms. If 1000 feet has .24 ohms, 0.1714 will be 714 feet long. This is the total length, so the cable length will be half, because there are 357 feet in each of the hot wires. So it is needed a # 4 AWG 3 conductors cable ( very heavy), max 357 feet long 

Two leads of this cable can be connected to the 50 A CB upper terminal screws through a 80 A CB, to protect the generator and the third to the neutral and, if it is possible an industrial (pin and sleeve) connector for 80 A ( very expensive and difficult to find).

Regards


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## Osviur

Hi,

This is the connector type needed to carry the generator full power, using a #4 AWG x 3 cable:










http://www.elecdirect.com/pin-sleeve-devices/100-amp-pin-and-sleeve-devices

With a 80 amp connector is enough.

Regards


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## thehandyman1957

So if he only needed to go less than 100 feet 6 gauge would be fine right? I would be curious to know what gauge wire is coming out of his generator going to the 50 amp breaker.


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## Osviur

Hi thehandyman1957,

Glad to explain you how to select a cable for any simple application.

Factors to consider: Power to be transmitted, voltage used, distance to transmit,ambient temperature, material that will surround the cable (air, earth, pvc duct etc)

Power in watts divided by voltage, gives amperes (at power factor =1) 17500 / 240 = 73 A (max) 
. 
Using a table like this one:

Wire Gauges - Current Ratings

Under Typical max current, column 3 cores (conductors) find the current to be transported (70 A in this case). following the 70 line, to the left. first column: #4 AWG.
This means that the minimum wire size to carry 70A is a #4 AWG.
Now max voltage drop admitted. 5% is a very good percentage. It means that we will accept a minimum voltage of : 240V - 5% =240 V supplied minus 12 V (voltage drop) = 228 V .
Using Ohms law to determine the max resistance admitted for the total length of the cable = 2 x distance, 

R (Ohms) = Voltage drop / max current = 12 V/ 70 A = 0.1714 Ohms
In the table : Ohms per 1000 feet (press the blue letters) for a #4 AWG : 0.24 Ohms / 1000 feet
So we can not use 1000 feet of # 4 AWG gauge, because we will obtain a voltage drop of: V drop= 70A x .24 = 16.8 V
and 240 V - 16.8 V =223.2 V, more than the 5% established.

Calculating: if 1000 F have .24 Ohms, then 0.1714 Ohms (Max resistance permitted) will be 714 feet long. This the total conductor length, using two conductors, we can reach just half this length: 357 feet.

If we need more than 357 F , and carry 70 A too, we will select a thicker conductor as a #2 or so to get more distance.

A #6 conductor carries 55 A as max curren, so in this case it is not usable to carry ALL the current generated by this 17500W machine.It will carry a max power of : 240V x 55 A = 13200 W

Regards.


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## thehandyman1957

Wow, thanks for clearing that up for me. One question, when it refers to (cores) is that referring to how many lines are in a said cable? Is this chart for like say a 6/3 or 4/3 cable? 

The reason I ask is that it does refer to a single core handling a lot more. If a person uses a conduit and 3 single core lines, is it still considered a 3 core run? My understanding is there is a heat factor in this chart and thus having cables intertwined would not be able to disperse the heat as well as a cable by it's self or not wrapped up in a housing. 

Thanks


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## Osviur

thehandyman1957,

Thanks a lot for the attention paid . You are right, this table points to one or multiple wires (in touch between them) contained by an insulation cover, and the different current capacity is, as you say, for the different heat transfer characteristic, being the most efficient the solid one.

Sorry I am short in time this morning I'll be back in the night.

Regards


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## Osviur

Hello Handyman,

Coming back to the Forum…. The previous table refers to to the number of wires contained in a conductor, from solid to extraflexible, but not not the number of conductors in a cable.

The National Electric Code, Art.300.15 establishes the maximum current capacity in amperes (ampacity),for the different AWG numbers and insulation type. In this page:

http://www.usawire-cable.com/pdfs/nec ampacities.pdf

We can see these values. In the heading is specified that this applies to not more than three current carrying conductors in a common raceway, cable (our case) or earth. For the 17500 W gen, we will use two current carrying conductors plus a neutral (120-N-120)
There are many types of insulation covers for the copper (or aluminium) conductors. The most common and simple is the TW Insulation (Thermoplastic Wet). It has the lowest operating temp rating (60°C) and for a # 4 AWG it limits its max current to 70 A . A THHW will operate at 90°C carrying 95 A.
The temperature rising is the effect caused by the electric power developed inside the conductor. This power in watts is proportional to the conductor resistance (ohms) and to the current transported (Amp) squared.

Thanks again


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## thehandyman1957

Well, that clears it up then. #4 it is. Thank you for your time and information.


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## Osviur

Mr Handyman,

You are welcome, thanks to you.


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## mark raymond

Art Ramirez said:


> Ladies and Gentlemen:
> 
> I have an older Generac 17,500 watt portable generator which I want to use as standby/backup hardwired into my electrical panel.
> 
> Can the generator be rewired to by pass its outlet panel and provide one set of leads that will provide full generator output to be hardwired into the house panel?
> 
> Thanks
> 
> Art


did you complete the project?


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## FlyFisher

mark raymond said:


> did you complete the project?


Old thread. Looking up the OP's details:
Last seen Jul 19, 2017

If he hasn't been back here in ~4 years I am not sure he will reply.


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## mark raymond

FlyFisher said:


> Old thread. Looking up the OP's details:
> Last seen Jul 19, 2017
> 
> If he hasn't been back here in ~4 years I am not sure he will reply.


well, I am proceeding with the project. If you here a loud buzz and sirens you'll know i failed.


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## FlyFisher

mark raymond said:


> well, I am proceeding with the project. If you here a loud buzz and sirens you'll know i failed.


Buzz and sirens post-mushroom cloud? 

There might be a terminal strip inside the electrical box where the leads from the alternator (directly from inside the alternator) terminate and where the distribution wires join up. Your breakers on the generator are fed off of that terminal strip.

Depending on how your generator is set up, you might have multiple "main" circuit breakers - like a 30 amp and a 50 amp. If the 30 amp is fed from the 50 amp breaker then the 50 amp would be your "main line circuit breaker" = it is the limiting factor to the amperage/wattage you can push from the generator (12,000w running). If your 30a breaker, in the theoretical example here, is not fed off the 50a breaker, but is its own circuit off the alternator, then you have the possibility of running another 7200w. If you are hooked in to the 2 circuits that would total 12000+7200 = 19200w. That is more than your generator is spec'd for. So what would make sense is if your generator, say, at 17,500w starting will provide 15,000w running - put a circuit breaker on it that will let you run 15,000w, or 62.5 amps. Since breakers don't trip exactly at overload, rather they are delayed based on heating, it would make sense to use a 60 amp breaker. That would let you draw peak power up towards the peak starting of your generator, but would protect the alternator from running continuous power beyond what the alternator is spec'd for. 

As to how you get from the breaker to where your power distribution is - thats up to you and what is acceptable in your situation. I presume if you are chasing after the project you aren't concerned with making stuff work yourself, but use your head and do your research. If you are having things inspected - maybe investigate codes etc and run the ideas past someone that can guide in that regard.


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## mark raymond

the generator is rated for 17500W (72.9A @240v) continuous output. the line side of the 50 amp breaker is used as a junction for the connection of the generator power supply to all the outlets. the entire generator output goes to the line side. I plan to disconnect the 50 amp breaker and replace it with a 70 amp (IEC60898, tripping curve C -same specs as the 50 amp), and then either disconnect or just not use any other outlet when I am using the main outlet.

The current installation uses 8 gauge boat wire to connect the hot lines from the breaker to the 50 amp outlet. I plan to either not use the outlet at all, or if i do keep the outlet to replace the wire with 4 gauge. I'm using 4 guage SOOW to my load.


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