# 3 wire to 4 wire generator connection possible?



## dmxtothemax (Oct 26, 2010)

jws3 said:


> Hi, all-
> 
> Despite a search I didn't see the answer to this, so I'll ask away.
> 
> ...


If you connect the two hots together,
Then any 240 volt loads will get nothing !
So your 240v loads will not work !
So no it will NOT work !
The only time it would work, 
is if there were no 240v loads
Just lots of 120v loads.
That is if code allowed you to do it !
Which I doubt !
If you have 240v loads,
you must use a generator with a 240v output !
No easy way out !


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## jws3 (Feb 15, 2007)

*But I don't want 240v all the time.*



dmxtothemax said:


> If you connect the two hots together,
> Then any 240 volt loads will get nothing !
> So your 240v loads will not work !
> So no it will NOT work !
> ...



What you suggest is exactly what I want.

I have only one 240v load, which is seldom used, but requires a larger generator when needed. I realize fully that taking a 3 wire (hot, neutral, ground) and adapting to a 4 wire (2 hots x+y, ground & neutral) will keep me at 120v--which is exactly what I want when using a smaller & far more fuel efficient generator. When the adaptor harness is used the sole 240v circuit would be shut off. The whole point by running a jumper from the x to y is to make it a 120v only. I did a test with this and it worked perfectly, so long as the sole 240v breaker was off.


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## zappa (Nov 25, 2011)

You need to be careful if you have any circuts with a shared neutral as your setup would place too much current on the neutral.

You would be ok with a 2000 watt generator but just be aware of this fact if you ever went larger.


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## mpoulton (Jul 23, 2009)

As Zappa says, this solution has the potential to overload the neutral of a multi-wire branch circuit. Those circuits rely on the two hot legs being out of phase, so the loads on two legs cancel each other out instead of adding to each other. As long as your generator can't supply more than 20A, this shouldn't be a problem - but don't wire in a 6500W generator that way! Otherwise, your solution is just fine and is commonly done.


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## jws3 (Feb 15, 2007)

*Thanks for the comment=got a question*



zappa said:


> You need to be careful if you have any circuts with a shared neutral as your setup would place too much current on the neutral.
> 
> You would be ok with a 2000 watt generator but just be aware of this fact if you ever went larger.


Thanks-- I do not understand what "shared neutral" means. How would one tell what circuits do or do not?

Only one circuit on the gen tran panel is 240v. Every other is 120v only. I may not understand the theory, but do know that 240v from a 120v source is a bad thing! Just trying to save gas & allow it to last longer if need be. Can't see running a 6500 generator for just the fridge, radio, light & cell phone charger. I keep the big one for the well and furnace.

Ah- a little google time helps to sorta-kinda explain the concept of shared neutral, although why one would do so is a mystery. I doubt there is a shared neutral. The gen tran box came with 6ga power inlet wires and but 10ga neutral & ground leads, which I already replaced with matching 6ga leads. I figure wire gauges should match.


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## zappa (Nov 25, 2011)

The breakers of a shared neutral circuit "should" be next to each other and the levers "should" be connected connected together like a double pole breaker. The only (easiest) way to be sure is to look in the panel and see if 2 breakers are sharing the same neutral. It's normally a wire saving thing to run XX/3 to supply 2 circuits.


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## zappa (Nov 25, 2011)

I have a similar situation as yours but it's for a 120 volt trailer at my remote property. I was using a 5000 watt generator that I already had and it was using about 3 to 4 gallons per weekend just to keep the batteries charged and run the fridge. I bought a tiny little $99 Harbor Freight generator and my gas usage went down to about a pint. It won't run the microwave or A/C though.


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## jws3 (Feb 15, 2007)

*Glad to see I'm not alone--but $99?*



zappa said:


> I have a similar situation as yours but it's for a 120 volt trailer at my remote property. I was using a 5000 watt generator that I already had and it was using about 3 to 4 gallons per weekend just to keep the batteries charged and run the fridge. I bought a tiny little $99 Harbor Freight generator and my gas usage went down to about a pint. It won't run the microwave or A/C though.


Glad to see I am not alone in my thoughts. Just can't see running a large 6500w generator for a fridge, etc. 

$99 for a generator? I thought I got a good deal on the Honda Eu2000 for $900 (MSRP $1150)! $99? Gotta check that out. I'd be immensely concerned about reliability & longevity for $99.

Edit- just checked it out- They have a 900 watt for around $100, but its a 2 stroke and listed at 91db!! The Honda is something like 58dB and eerily quiet. Wow that 91dB must be LOUD.


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## zappa (Nov 25, 2011)

jws3 said:


> Glad to see I am not alone in my thoughts. Just can't see running a large 6500w generator for a fridge, etc.
> 
> $99 for a generator? I thought I got a good deal on the Honda Eu2000 for $900 (MSRP $1150)! $99? Gotta check that out. I'd be immensely concerned about reliability & longevity for $99.
> 
> Edit- just checked it out- They have a 900 watt for around $100, but its a 2 stroke and listed at 91db!! The Honda is something like 58dB and eerily quiet. Wow that 91dB must be LOUD.


It might be the same model although I think mine is super quiet compared to my loud 5000 watt construction generator. Normally $135 but sale and a coupon brought it down to $99. Been sitting outside for 2 years now and it has never let me down yet. I liked it so much that I bought another one that I keep in the barn.


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## biggles (Jan 1, 2008)

you can split the 120 BLACK into the panel just watch the amperges cause it is all going back on that WHITE single neutral,knocking off that well pump is cool don't need a generated 120V in a black out going out there...if your in a night time run including heating the 2000W is fine. might want to amp both sides of that split 120V simulating what is actually on to see what the neutral is sending back.i have a 3500W with 100' of 4#6 up a driveway under ground into my house panel use the black/red for each 120V side and the one white neutral back


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## Brianinpa (Oct 28, 2012)

The biigest problem I have is the gen panel. When using 2 phase input, all is well, but 1 phase means not only no 2 phase, but alternating breakers are cold. I wanted to migrate cold ones to hot positions, but the panel is not big enough. :-/ 

So I guess I can replace the panel, buy a bigger gen, or do without some things. If it's necesary, I can always swap colds and hots as needed, but thats a pita.


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## jws3 (Feb 15, 2007)

*Don't quite follow you*



Brianinpa said:


> The biigest problem I have is the gen panel. When using 2 phase input, all is well, but 1 phase means not only no 2 phase, but alternating breakers are cold. I wanted to migrate cold ones to hot positions, but the panel is not big enough. :-/
> 
> So I guess I can replace the panel, buy a bigger gen, or do without some things. If it's necesary, I can always swap colds and hots as needed, but thats a pita.


I don't quite follow. Are you looking for 120 only or 240? My small 120v only generator can be used on both 120 legs of my panel via a homemade 3 to 4 wire cable/connector assembly. It CANNOT be used for any 240v loads. I shut these breakers off when using it to prevent damage/overload. All I did was jump the X & Y hot leads in the 4 prong plug to do this. Don't always need a bigger 4 prong generator, so this does the trick.


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## stickboy1375 (Apr 28, 2012)

Buy a 120v reliance transfer switch, and someone qualified install it for you.


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## stickboy1375 (Apr 28, 2012)

jws3 said:


> I don't quite follow. Are you looking for 120 only or 240? My small 120v only generator can be used on both 120 legs of my panel via a homemade 3 to 4 wire cable/connector assembly. It CANNOT be used for any 240v loads. I shut these breakers off when using it to prevent damage/overload. All I did was jump the X & Y hot leads in the 4 prong plug to do this. Don't always need a bigger 4 prong generator, so this does the trick.


You dont even know the dangers of this....


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## jws3 (Feb 15, 2007)

*Already have one*



stickboy1375 said:


> Buy a 120v reliance transfer switch, and someone qualified install it for you.


Already have a gentran box with proper 4 prong wiring for use with larger Honda generator. The problem, however, is when I want to use a much more fuel efficient 2000 watt Honda for modest loads like just a fridge & lights. Since this is a 3 wire set up it cannot plug directly in the gentian inlet box, hence my adapter cable. I called gentran & they told me this is what many do (even the guy who answered the phone, if I remember right) although they can't officially recommend it. 

The 6500w Honda uses approx 1 gallon every 3 hours, while the 2000w model 1 every 9 hours. Why use the big one all the time when its higher output is only needed for the well pump and furnace? Hard to store enough fuel to run the big one all the time.


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## stickboy1375 (Apr 28, 2012)

jws3 said:


> Already have a gentran box with proper 4 prong wiring for use with larger Honda generator. The problem, however, is when I want to use a much more fuel efficient 2000 watt Honda for modest loads like just a fridge & lights. Since this is a 3 wire set up it cannot plug directly in the gentian inlet box, hence my adapter cable. I called gentran & they told me this is what many do (even the guy who answered the phone, if I remember right) although they can't officially recommend it.
> 
> The 6500w Honda uses approx 1 gallon every 3 hours, while the 2000w model 1 every 9 hours. Why use the big one all the time when its higher output is only needed for the well pump and furnace? Hard to store enough fuel to run the big one all the time.


Im a professional, not sure what else to tell you about that setup.


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## jws3 (Feb 15, 2007)

*Please expound if you would.*



stickboy1375 said:


> You dont even know the dangers of this....


GenTran & the local Honda service dealer were fine with it--they even suggested it! What are the dangers of using a smaller generator to power select circuits via the transfer panel assuming all 240v breakers are off?

If I am missing something bad I'd certainly want to know! Can't see having 2 transfer panels with one for each generator.

Thanks!


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## jws3 (Feb 15, 2007)

*What else can one do?*



stickboy1375 said:


> Im a professional, not sure what else to tell you about that setup.


I must be missing something. Is there a better way to use a smaller, more fuel efficient generator with an existing 4 prong GenTran panel? Seems inefficient to run a larger, more gas guzzling unit for just the fridge & a few lights. 

If there is a better & safer way I'd sure love to hear it. While I value efficiency I don't want danger or a lack of safety. GenTran (unofficially, of course) said no issue as long as 240 breakers are off as did local Honda techs and a local electrician I spoke to. Yes, there are certainly issues if over used, but given the smaller units 3 fold less fuel usage I prefer to use it whenever possible.


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## stickboy1375 (Apr 28, 2012)

you could overload a MWBC neutral by using a 120v generator the way you described.


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## Brianinpa (Oct 28, 2012)

Nah. Imma just do it right and get a fixed position genny. But good to know. AND a bigger panel.


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## jws3 (Feb 15, 2007)

*An excellent point*



stickboy1375 said:


> you could overload a MWBC neutral by using a 120v generator the way you described.


Great point. I recall now researching this back when I first posted this. If I remember the conversation right with the local guy each of my breakers/circuits has a dedicated neutral. None are shared, again assuming my memory is good. 

I do appreciate your comments. Trying to find the best solution without compromising safety.


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## stickboy1375 (Apr 28, 2012)

jws3 said:


> Great point. I recall now researching this back when I first posted this. If I remember the conversation right with the local guy each of my breakers/circuits has a dedicated neutral. None are shared, again assuming my memory is good.
> 
> I do appreciate your comments. Trying to find the best solution without compromising safety.


The only way is the right way...


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## jws3 (Feb 15, 2007)

*True, but is there a solution?*



stickboy1375 said:


> The only way is the right way...


I cannot philosophically disagree. But, is there a way to use a smaller, much more fuel efficient generator on an existing panel? Can't store enough fuel to the big one for nearly as long as the small one.

Seems silly to have the correctly installed gentran panel, all wiring done right and then bypass it all by using extension cords for the fridge & lights when using the small generator.

Is there a different or better way? Must I always use the big, gas sucking generator even when all I want is the fridge & a light or 2? There has to be a better way......


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## jws3 (Feb 15, 2007)

*Fixed genny?*



Brianinpa said:


> Nah. Imma just do it right and get a fixed position genny. But good to know. AND a bigger panel.


Can't see spending many thousands for a fixed backup, especially since we have no gas/propane. Its gasoline or nothing for a generator, unfortunately. Besides, I already own two Honda inverters which I can take with me if I move. 

I am puzzled on why one would need a "bigger panel", however. If I have a properly sized panel, proper back up gentran box & correct wiring why would I need a bigger panel? I'm not trying to skirt things by backfeeding or something equally dangerous. Just want to at times use the back up panel with a smaller, more fuel efficient generator.


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## stickboy1375 (Apr 28, 2012)

jws3 said:


> I cannot philosophically disagree. But, is there a way to use a smaller, much more fuel efficient generator on an existing panel? Can't store enough fuel to the big one for nearly as long as the small one.
> 
> Seems silly to have the correctly installed gentran panel, all wiring done right and then bypass it all by using extension cords for the fridge & lights when using the small generator.
> 
> Is there a different or better way? Must I always use the big, gas sucking generator even when all I want is the fridge & a light or 2? There has to be a better way......


I would pick a setup for whatever generator you want to use and stick to it.


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## jws3 (Feb 15, 2007)

*I started with the 6500*



stickboy1375 said:


> I would pick a setup for whatever generator you want to use and stick to it.


All was set up for the 6500W unit and then I experienced how much fuel it could use, even on the ECO setting & as an inherently more efficient inverter. Realized that 90% of my needs could be met with a 2000x unit so long as I had the bigger one for the well, hot water & furnace. With a wood stove even the furnace circuit is seldom used. 

At 1/3 the fuel consumption the smaller one has a certain appeal, even though totally unusable when one needs higher amounts of power. Don't want to compromise safety and am puzzled why the gentran people, Honda & local electrician all had no issue provided I use it as described. Yours is the first substantive concern I've seen, hence my alarm. Of course, all this talk on the TV about power outages got me thinking!

I wish the panel could be designed to accommodate everything!


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## jws3 (Feb 15, 2007)

*update*

Update: while I philosophically dislike mwbc circuits, I do have some. I've scheduled a trusted electrician to come by and inspect/change my panel as needed. Gentran makes NO mention of watching out for mwbc circuits in the install instructions. Still undetermined is if I moved only half or both sides of any mwbc circuits & if such is an issue under either line power and/or gen power. 

I am annoyed. All this BS because the original electrician took the easy path. Yes, i know mwbcs are common, but I still do not like the idea.


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## jws3 (Feb 15, 2007)

*Additional update: Had the setup inspected*

To allay any concerns, I had the gentian panel & wiring, etc. inspected by a local licensed electrician. He acknowledged that there are indeed some MWBCs in the box and which are hooked up to the gentran panel. We also discussed my desire to use a 3 to 4 wire cable adaptor for circumstances where the larger, much less fuel efficient generator isn't needed and the concerns expressed here by some.

In short, he agreed that those concerned with an overload of a MWBC are theoretically correct, but given the maximum 16A output of the smaller Honda generator (13.7 continuous) there is little, if any, real world risk of an overloaded neutral even under worst case scenarios. Were one to connect a much higher output generator with a 3 to 4 wire adapter & run crazy loads on those circuits sharing a neutral an overload could be a risk. Since I have no intent of doing such, nor do I even own a 3 wire generator capable of such high output all should be, or so I hope, fine.

Thanks to all for the comments & discussion.


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## Macken (Nov 29, 2012)

stickboy1375 said:


> You dont even know the dangers of this....


There really are none :thumbsup:



stickboy1375 said:


> Im a professional, not sure what else to tell you about that setup.


I'm a professional too, or at least a licensed electrical contractor :thumbup:

The setup that he described is perfectly normal and commonly used. I do it myself.



stickboy1375 said:


> you could overload a MWBC neutral by using a 120v generator the way you described.


Impossible. The generator is only capable of delivery 2,000w (16.6A) for a short period of time. The generator is simply not able to overload the neutral of a MWBC.



stickboy1375 said:


> The only way is the right way...


There is nothing wrong with this way. I understand that it seems wrong on the surface, especially to an electrician, but it's not.



stickboy1375 said:


> I would pick a setup for whatever generator you want to use and stick to it.


Again, I have to disagree. I do pretty much exactly what the OP does, I run a Honda EU2000i full time and only connect my large generator when I need water or heat. This system worked well for me for over 12 days last month, and many other people.


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## jws3 (Feb 15, 2007)

*Thanks, Macken, for the comments.*

Macken, 

I appreciate your comments & taking the time to do a detailed response. The fact that it didn't talk down to me as I've had in the past is also appreciated. I'm here to learn, not be right! I learned about MWBCs in this thread and have taken steps to remedy any mistakes. For this a appeciate the time & efforts of all those who posted. The last thing I want to do is fry the family. 

I'm even going farther than the electrician suggested & double checking that whatever circuits I have on the Left lug are on the A gentran lug and those on the Right lug are on the B side. This is to ensure that any circuits routed through the gentran panel maintain MWBC polarity for when I do use the larger EU6500. There is one minor lighting circuit that on second look may not work out due to an insufficient number of B side breakers, so I may remove it. I called the electrician back on this who sees no real world issues, but I like to be safe.

Your analysis matches mine. I do see where the other pros here are coming from & agree that there would be a danger with a larger generator. There is NO WAY I'd put 40 amps through a 3 to 4 wire adapter set up. As a result of this thread I've cancelled plans to purchase a second EU2000, which I had toyed with using in dual synch mode for 27.4A (3200W) continuous / 33.2A (4000W) surge output. That's too much, which I won't risk. 

Glad to see your EU2000 worked out so well. I've only needed mine once "for real" and noted a drastic cut in fuel use over the already very efficient for its size EU6500 I also own. You used yours for 12 days. At 18 hours use per day that's about 2 gallons. To do the same with the 6500, never mind the gas guzzling "standard" gen sets and we're talking 6 gallons, a 3 fold increase. A cheaper "standard" gen set would use perhaps 12 gallons per day or more! Over 12 days thats a lot. Again, it isn't the fuel use & cost that concerns me, but availability. In most outages gas stations also shut down or, if the outage lasts long enough and as we've seen on the news, run out of gas. The only times I might need the bigger generator is when running the well, microwave and/or heat. But, I have a fireplace, which generally heats the house down to about 35. Below that the heat will tend to come on.

Got to be a fan of these inverter Hondas. Way quieter and more efficient than anything else out there, although I hear the Yamahas are good too. Just harder to get parts for them, which is why I went with Honda.


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