In my other thread HERE, I am running for a week off-grid on generator power for construction reasons. 

We are using a 9k Champion duel fuel generator. Its working wonderfully, but honestly it sucks a TON of fuel.

Most of my loads are small enough for my 3750 running watt Briggs generator to handle easily, especially evening/night time. The only issue is the Briggs doesn't have a 240 plug, only a 30 amp RV plug and standard 20 amp plugs.

So here is my question for those more knowledgeable on the subject: While I know I can't power any of the 240v appliances, can I make a cord to power both legs of the box from my 30 amp 120v RV plug on my small generator? It would save a considerable amount of fuel over the next 5+ days. I was thinking of making a cord and just using a jumper wire to power both hot legs of the 240 plug?

I'm off to Menards (like a Home Depot) in a hour, so a shopping list quickly would be appreciated, if this is possible!

Thanks,

EDIT:

TL/DR version/instructions:

You can power both legs of your main breaker panel with a 120 generator. Your 240 appliances will NOT work, and should have the breakers off when doing this. Don't want to damage stuff..
So how it is done:
All you are doing is making a special adapter that connects both legs of the 10/4 cable to the one hot on the 120v plug. Lets assume you have the standard 30 amp 4 wire generator twist lock connection. This will NOT be modified, nor will any changes happen in your panel. The ONLY changes are a special adapter you will make. First, you need to get yourself a female twist lock adapter. They are some $30 at Menards, ordered one from ebay for $11 shipped. I bought it from this seller. It functions just fine. Second, you will need the type of 120VAC plug that your 120 volt generator has. Mine is an "RV Ready" generator, so it has an RV 30 amp plug. Replacement plugs are available at Menards for me, shop around if you have to. Make sure you get one where you have some room to work inside. Mine looks mostly like this:
 
After you source your two plugs, you need some wire. Ideally, it is 10/4 SOOW rubber wire. You can get it by the foot from this seller. You only need 1 foot, two if you really want to.

The next step is simple. On the 240 volt 4 wire plug side, wire it as normal. You should have the following symbols: W,G,X,Y. The W is for the white (neutral) wire. The G is for the green (ground) wire, and X and Y are your two hots, which should be black and red. Doesn't matter which goes to which.

On to the 120volt plug. This is where the magic happens. The inside of my plug has the same lettering symbols except instead of X and Y, I have a B for black (hot), yours should as well. The ONLY difference (and the entire mod) is both the red and black wires get put on the hot terminal. Neutral (white) and ground (green) are connected as usual.

The inside of the 30 amp 120v plug will look like this:
Attached File


This adapter should be marked with some kind of warning label with exactly what it is and what it does.

All said and done, you adapter will look like this:
Attached File


That's it! 
Now when you want to run your smaller 120v generator, all you need to do is insert this special adapter onto your standard twist lock 240 cord, and then into your RV ready generator. Now you have both legs powered! In theory, you could even get an RV 30 amp to 15 amp adapter and run just a couple lights and maybe a fan at night with the little Harbor Freight 2 stroke generator, or other small generator with 15-20 amp plugs. 

Water Heater to 120VAC mod:
DISCLAIMER: Please keep in mind I did this on an old, standard hot water heater that will never be used again once we move. I'm not responsible for any damages from you playing around with stuff, and this is almost a "permanent" mod, as wires are changed in your breaker panel. Also, this may/may not be to electrical code. My house is off grid, not connected to the utilities in any way.

This one is simple. My water heater has 3 wires: 2 hot and a ground. All I did was open up the breaker panel, put one hot wire to neutral, replace the dual breaker with a single I had as extra, connect the remaining hot wire to new breaker, and re-energize the panel.

The reason I did this was the water heater heavily taxed my generator, as in within a few hundred to a thousand watts of capacity. Also, I can now run the water heater with my 120v generator. By doing this, power consumption is reduced by 75%. The flip side is it takes that much longer to heat the water. Physics and all.... One the major plus side, the water heater can now run while the generator is running other appliances. We had to power down everything else before.

Like I said, this one is not just an adapter.

Phase issues I'm thinking. I don't think you can do it.
In for the answer...

How many gen heads are you willing to blow up, or how many appliances are you willing to destroy?

240V single phase is NOT simply 2 120V lines.  The 120V lines need to be phased properly. And conductors sized properly.

I imagine if you could break into the gen head you might be able to re-tap it to get 240V. I wouldn't advise it.

Better would be to get a small transformer.

Nevermind - got it into my head that OP was trying to get 240 from 120.

So I just remembered that I had a funky adapter for my park model RV, which uses a 50 amp 240 plug since that park model is 240/120.

It has a 240v 4 prong female end and a 120v 30amp RV end.

Is this not basically the adapter I need?

Hmm, now that I think about the phase issues...

But no 240 appliances would be energized, just lights, bedroom fan, fridge...

Any more opinions? 

Sure you can.  

Simply disconnect [trip breaker] all the 240 volt loads.

Both sides of the distribution box will now have the same 'phase' vs. neutral.

No genny heads will be damaged in this experiment.

lol


And in  actuality, you wouldn't have to throw the 240 devices' breakers, since they won't draw any current.

This said, for a noobie, I'd flip them anyhow.

You would need to be sure that you had a good nuetral along with the 120volt feed. 
Your rv plug probably does not. 

Well...

If you backfeed through a 120V outlet, that means that one side of your panel will be energized. So if everything you needed to power were on that side, you should be ok, provided you shut off any 240V breakers.

And, I suppose if you fed another outlet on the other side of the panel with 120V, that side would be energized too.  As long as the 2 sides of the panel were electrically isolated from each other...

I can say this - if it were me, I would spend so much time checking every connection in that panel with a voltmeter that it would be faster to wind my own transformer.

No phasing issues since its only 120 volt. 
Definitely open all your 240 volt breakers along with your main though !

Skip the cheap RV plugs, etc, and buy some wire to connect directly to the panel.

What would you suggest Rat use for the transformer core????

Why folks post about stuff they have little understanding of is beyond me.

If he fed the 2 hot legs , on his 240v feed , with 120volt each it would feed both sides of the panel. 

The nuetral is the problem. 

RV adapters are odd to begin with. From what I've seen, there is no 240v in an RV. If you aren't very familiar with your generators outputs and your appliances,  I wouldn't do it. Use a voltmeter at any connections before plugging in your appliances.  And check for voltage to ground after powering up. I learned a very costly lesson regarding RV adapters once. RV adapters belong in RVs and RV parks. 

paging @ar-jedi


He did it in his genny and Sandy hurricane page.
I followed suit.

Hook up a crossover cable that has L1 and L2 both connected to the 120VAC Hot.
Then when it's hooked up to your panel both sides have 120VAC.
The 240VAC breakers would have 0V if they were turned on.

https://www.ar15.com/forums/outdoors/Sandy-12-days-without-power-what-worked-what-didn-t-/17-661411/&page=1#i11295550

Obviously he has to connect the neutral or nothing would power up!

Exactly!

Well, that's one of several ways to do it...

Yes, there are 240 volt "RV"s. It is a park model, basically a small mobile home but legally a "recreational trailer". It has a 240/120 panel, and Menards sells the adapters to go down to the 240 twist lock or the 30 amp 120v.

The rest is what I'm not sure about. Household AC systems are not my strong suit.

What is your specific question now?

Not really a viable option for a one-off. Plus, I'd rather have a cord that I control and know how to use properly so the wife/kids don't mess with stuff and screw something up one day.

Yes , however if he doesn't have one on the cord then he can't connect it ..

https://www.ar15.com/forums/outdoors/Sandy-12-days-without-power-what-worked-what-didn-t-/17-661411/&page=3#i11303530

Can I use this adapter that goes from a 30amp 120v RV plug to a 240v 50 amp RV plug, buy the adapter to go from this to my twist lock 240 plug, to power both sides of my box to run 120v loads?

Attached File

Do a continuity test.
The hot side of the 3 prong plug should connect to both hots of the 4 prong outlet.
If that is the case, it should work.

First, you MUST ABSOLUTELY disconnect your home from the power lines and any source of 240V. Fire, destruction, death etc may results if you do not do this. Turn off main breakers, disconnect at the meter, whatever is necessary to absolutely ensure that you are not connected to regular power.

Then, no problem. Connect your 120V hot side to both sides of the 240, and neutral to the center neutral. All 120 will therefore be powered, and anything 240 sees no voltage since the 240 is shorted together.

Most people will say that you have to turn off all your 240 breakers, you can if you want but it won't matter. With the two sides of the 240 shorted together there is zero volts there. If you have something like an electric stove, the 120V lights would still work but the 240V burners would not.
If you have any sort of wiring skills, I would get the correct plugs for each end and make a cord to do what you want. My experience is that you need to minimize the number of plugs, adapters etc to minimize losses when dealing with a generator.  Make sure you use a sufficient gauge wire to handle the current draw.

That was hyperbole. My first suggestion was buy a transformer.  The "wrap one" comment was in reference to the time it would take *me* to be satisfied that things were safe.  I know full well that one can operate safely by limiting what appliances and circuits are attached.  But I'm not confident enough in my own situation to trust that.  That's why I led with "if it were me."

Lines be cut from the grid at the moment, so no worries on that one 

Boy are you making this hard.

If that's the plug that fits the genny, AND IF THE BLADES ARE---

120VAC HOT : 120 VAC NEUTRAL : and COMMON/EARTH/GROUND/whateveryouwanttocallit---


Cut the adapter cord in the middle, splice/wirenut it to the long cord you are running from the genny to your house, and connect to your panel.

Done.

Wouldn't you get stray current flows when the load gets imbalanced and the generator lugs momentarily?  Maybe 5-10V for a second or two, like when a refrigerator compressor kicks in?

No- You seem to be overthinking this

This. If you have the two sides of the 240 shorted together, there cannot be any voltage there. This is no longer a split phase 240V system.

If it would be feasible/convenient to wire a heavy cord directly to the breaker panel from the generator that would be ideal and save any losses from extra plugs or wire run.

It was a genuine question out of curiosity. I get voltage sags in my house when wall air conditioners kick on, because of the previous owner's wiring.  It seems to be isolated to a single circuit. (and yes, I finally mapped all the wiring and am going to be pulling new circuits in spring.)

I have no idea if such a small voltage for a short time would matter at all - I was more asking about the flat assertion of 0V at the 240V breakers.

How does the load get imbalanced?

By connecting L1 and L2 you turn a 240VAC panel into a big 120VAC panel.

All of the breakers and their associated circuits are now in parallel.
The 120VAC generator L feeds all circuits simultaneously.
If you draw too many amps for the genny to handle it'll kick off line or trip the breaker.

You CAN'T run ANY 240VAC devices in this configuration.

That's because in normal configuration on grid feed you are powering two separate legs.  So load imbalances are possible.

Cut it in half? Its like a $50 adapter 

I'll just make my little jumper cord for putting the 50 amp RV plug to the twist lock 240 I have rigged up currently. They may even have that adapter already at Menards. That way when I have the permanent generator pad in place, I can have the big and little generators there and run between the two based on usage. Plus redundancy and all that..

I understand no 240v appliances will work due to phasing issues, but that isn't an issue with what I want. Just lights/TV/internet/bedroom fan/refrigerators.

That makes sense. I was thinking 2 cords from the generator-2 backfeeds, so the interconnect point between the 2 legs would be farther away and more subject to weirdness.

And honestly, I'm a mechanical engineer.  My solution to OP's problem would be to spend the time figuring out why the larger generator is using so much more fuel for the same load.

Because its a 16ish hp engine running at 3600 RPM. That takes fuel. My smaller generator is something like 1/3 of the displacement.

Hmmm, now I want to look up the BSFC of the engines.  Yes, a larger engine running at <full load generally has lower fuel efficiency than smaller at full load.  But it's generally not THAT much in gross terms.  But I've rarely dealt with small engines, mostly large gensets.

This method adds adaptability and allows you to structure your electrical production, and therefore fuel consumption, to meet the load.

I have a 7250W 240VAC generator and two Honda EU2000i's.

I can run a lot of things on the 240VAC generator at once, including a water heater if I have to, but if I'm just using the internet, TV, refer and some lights I'm burning a lot of fuel.
I can hook up one or both of the Hondas and get 13A to 26A 120VAC.  
So I can match the power output and fuel consumption to what I'm actually using.
All the way down to running a single Honda in econo mode.


I have an automatic refer battery backup too, but that's a different thread.

Yup, big difference in fuel consumption. We figured that one out quickly using our generators to run the RVs. I now even bring the little HF 2 stroker to run the lights on the RV. I can run all day on a gallon of fuel.

This is easy to do, get some cable and plugs at the big box store.

Or...
Premade Solution.

http://www.nooutage.com/adapt.htm

Well then, go be poor someplace else...

240VAC household is simply two legs off a single phase transformer. Its not two phase power.

I have a 3500 champion and a transfer switch. the transfer switch is designed to take a 4-prong twistlock with a 240VAC input. I built a custom generator cord that splits my hot leg into both L1 and L2. I have to open all 240 breakers in the panel but the rest of the circuits are fine. I think this is exactly what you are asking to do.

well it looks like this thread wrapped up nicely while i was off at work.  

ps

connecting a 120Vac-only generator to a 4 wire generator inlet in a way that powers both "halves" of the service panel...

the assumption up front here is that there is a transfer switch, or interlock plate, or some other safe means of isolating the generator feed from the utility feed.

so:

(NEMA 5-15P or NEMA 5-20P 120Vac plug) <-- some length of appropriate gauge cordage --> (whatever 4 wire generator female connector is required) -> which plugs into -> (whatever 4 wire generator male inlet receptacle you have)

in the backshell of the 4 wire female connector on the end of the cordset, use a short but stout "jumper wire" to connect L1 and L2 together.  (this may be marked as "X" and "Y" on the housing).

the "jumper wire" should be the same gauge as the wire in the cordset itself; nothing less than #12AWG (which is required for a 120Vac 20A circuit).

because i have EOCD (engineer-OCD, which is a diagnostic level above generic OCD ), i mark the end of the cable as having this "feature", and i turn off any 240Vac breakers in the service panel.

note: you can also do the above with a NEMA L5-20P 120Vac or L5-30P 120Vac plugs, which are common on some "industrial" generators.  and ditto for the TT-30, which is typical of camping generators.

ar-jedi

Why would he need a transformer?

Either way, doing what OP described will somewhat violate the code.
Let's say, I wanted to do a "redneck special" connection to the generator. I would simply use a male to male, regular 120V plug adapter, plug it into one of the receptacles.  Find one dual pole breaker, disconnect the existing wires and put a jumper between the poles thus interconnecting both "sides" of the panel. Open the main breaker and all the dual pole, 240V breakers in the panel. Start the generator and run it. Put a lock on the breaker panel, so no one can flip the main breaker on. Obviously, current capacity will be limited to your generator size and size of the breaker (and wiring) that feed the receptacle you plugged your "widow maker adapter into.
It's best to wire the generator directly to the panel, with proper size wiring. "Hot" to both 120VAC "sides" of the panel and neutral to the existing neutral. Obviously, connect generator ground to the panel ground.  Install a jumper between both "sides" of the electrical panel, remove the main breaker (or block it from being turned on while generator is running), open or remove all dual pole (240VAC) breakers and enjoy.
Do this at your own risk. Flipping main breaker on while generator is running, may send high voltage down the supply line and electricute whoever's working on the wiring. This is possible but linemen know this and usually ground the line they work on, unless they are isolated from ground. Precaution safety measures are taken anyway, no matter what.

Again, this is a "redneck special" and not a proper way to do this.

I did this when we were without power for a week after Sandy.  I'd run the 5kw 220 volt generator during the day and the Honda eu2000 at night.  I built an adapter cable using an L14-30 on the house side and a 5-20 on the generator side.  I put a jumper across the 2 hots in the L14-30 to power both sides of the panel.  I put several red warning labels on it so I would remember what it is for and not to plug it in during normal operation.  The only potential problem after turning off the breakers for any 220 appliances is the neutral.  The power company provide 220 as two out of phase 110 legs.  Since they are out of phase, 2 breakers, 1 on each phase can share a neutral.  If you are powering both breakers (that share a neutral) with a full 15 or 20 amps per breaker you could overload the neutral causing a fire.  I don't worry about this since my Honda can't put out more than 16 amps total.  YMMV
** Disclaimer** I am not an electrician or engineer, this is not advice and don't recommend anyone do anything I do)

^^^^ this is a bad idea for about 87 reasons.

ar-jedi

You won't overload the neutral if you size the wiring between the generator and the breaker panel,properly. It's best to use a 3 conductor ("hot", neutral and ground), 12 gauge cable for a 2,000W generator (thicker wire for long runs). Put the jumper on the breaker side of the cord. You can also use a 2 conductor, 12 Ga. cord and a separate grounding conductor. Grounding conductor can be of smaller gauge size. By code, neutrals are grounded at the breaker panel (usually) but a separate grounding conductor is required no matter what.
If your generator has a separate round (grounding rod), if must be tied to the house ground at the main SES panel (usually - main breaker panel).

Love these threads!

Yes but I said that it was a "redneck special" . A quickie to get a refrigerator running to keep beer from getting warm. The best choice would be to install a separate sub-panel and a transfer switch. The separate panel would have all the circuits you need energized when running a generator (either 120 VAC or 1240 VAC.
Guys, please get an electrician to do this for you if you are not familiar with electrical systems. Improper installation may cause fire, electric shock, death or even beer getting warm from lack of refrigeration. Do it right the first time and you won't need to do any "redneck special" wiring hacks.

BTW. Glad you decided to stick around on this forum.

Quick question to test your electrical knowledge: What will happen if you install a fuse upside-down in a single phase AC electrical panel?