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Old 01-17-2012, 10:02 PM   #1
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3 wire to 4 wire generator connection possible?


Hi, all-

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

Got a multiple back up generators- A Honda 6500 inverter and smaller 2K Honda inverters. The house is equipped with an L14-30 4 prong gen tran power inlet box and transfer panel for safety. No backfeeding allowed.

I only have the larger generator for the 240v well and, if needed, heat, which uses a 3/4hp motor to drive the blower on a 5 ton system.

Bigger generators use more gas. 90% of the time I can get by on far less. Generating capacity isn't the problem so much as fuel storage, so I'd prefer to use the smaller ones whenever possible.

Problem: Smaller generators tend to have only a 3 prong 120v receptacle, which don't play well with the 4 prong power transfer box. I thought of simply making a 3 wire to 4 wire cable & "jump" the x & y leads to give 120 to both sides of the panel. Of course, the well pump would HAVE to be off for this to work. Can't try to pull 240 from a 120v generator.

Any better suggestions? Kinda stinks to be forced to use a bigger generator than is necessary. Why run 6500w when 2-3K is all you need? half the gas means it can run twice as long.

Thanks to all in advance.

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Old 01-17-2012, 10:44 PM   #2
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3 wire to 4 wire generator connection possible?


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Originally Posted by jws3 View Post
Hi, all-

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

Got a multiple back up generators- A Honda 6500 inverter and smaller 2K Honda inverters. The house is equipped with an L14-30 4 prong gen tran power inlet box and transfer panel for safety. No backfeeding allowed.

I only have the larger generator for the 240v well and, if needed, heat, which uses a 3/4hp motor to drive the blower on a 5 ton system.

Bigger generators use more gas. 90% of the time I can get by on far less. Generating capacity isn't the problem so much as fuel storage, so I'd prefer to use the smaller ones whenever possible.

Problem: Smaller generators tend to have only a 3 prong 120v receptacle, which don't play well with the 4 prong power transfer box. I thought of simply making a 3 wire to 4 wire cable & "jump" the x & y leads to give 120 to both sides of the panel. Of course, the well pump would HAVE to be off for this to work. Can't try to pull 240 from a 120v generator.

Any better suggestions? Kinda stinks to be forced to use a bigger generator than is necessary. Why run 6500w when 2-3K is all you need? half the gas means it can run twice as long.

Thanks to all in advance.
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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Old 01-17-2012, 10:56 PM   #3
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3 wire to 4 wire generator connection possible?


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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 !

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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Old 01-17-2012, 11:08 PM   #4
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3 wire to 4 wire generator connection possible?


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.

Last edited by zappa; 01-17-2012 at 11:18 PM. Reason: more info
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Old 01-18-2012, 12:57 AM   #5
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3 wire to 4 wire generator connection possible?


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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Old 01-18-2012, 07:51 AM   #6
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3 wire to 4 wire generator connection possible?


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Originally Posted by zappa View Post
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.

Last edited by jws3; 01-18-2012 at 08:26 AM.
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Old 01-18-2012, 08:38 AM   #7
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3 wire to 4 wire generator connection possible?


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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Old 01-18-2012, 08:49 AM   #8
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3 wire to 4 wire generator connection possible?


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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Old 01-18-2012, 10:18 AM   #9
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3 wire to 4 wire generator connection possible?


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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.

Last edited by jws3; 01-18-2012 at 10:35 AM.
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Old 01-18-2012, 11:15 AM   #10
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3 wire to 4 wire generator connection possible?


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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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Old 01-18-2012, 12:31 PM   #11
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3 wire to 4 wire generator connection possible?


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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Old 10-28-2012, 01:25 PM   #12
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3 wire to 4 wire generator connection possible?


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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Old 10-28-2012, 01:49 PM   #13
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3 wire to 4 wire generator connection possible?


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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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Old 10-28-2012, 01:51 PM   #14
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3 wire to 4 wire generator connection possible?


Buy a 120v reliance transfer switch, and someone qualified install it for you.
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Old 10-28-2012, 01:52 PM   #15
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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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