I read this question, and it’s close to what I’m wanting to do but not quite.

We had a power outage due to weather. I purchased a generator that is 30 amperes but 120 V. Initially, I was going to wire this to allow power to come to both phases of my panel but I decided against it. I just opted for the bare minimum until the power came back on. I want to purchase a second generator and come up with a better solution in the future just in case.

The generator manufacturer makes a parallel kit but it appears to only double the output wattage not the volts which is understandable. I get that running 220 V can cause phase issues. That’s not what I want to do. I don’t care about running any 220 V devices during an outage. My hot water heater is the only 220 V device I missed and I’m swapping it out with a gas one.

Can I possibly buy two of these generators, the parallel kit, and somehow make a plug/setup that will allow me to have the combined 60 ampere capacity, still 120 V but on both legs of the power?

I realize that a standby generator and transfer switch is the way to go but I don’t want to spend that much money.

  • 2
    \$\begingroup\$ I’m confused, you state the manufacturer supplies a kit to enable the two generators to run in parallel at 120v. Then you ask if you can buy a kit with two generators to do exactly what you say is available... \$\endgroup\$
    – Solar Mike
    Nov 16, 2018 at 15:46
  • \$\begingroup\$ Yes you can parralel gens together as long as the phase is aligned else you will nuke them. Don't know what you mean by both legs of power? Please clarify. \$\endgroup\$ Nov 16, 2018 at 15:53
  • \$\begingroup\$ I think he's referring to the split-phase power coming into his panel. Normally the two 120 legs are 180 degrees out of phase, in this case they wouldn't be (ie no 240 at all). \$\endgroup\$
    – user201365
    Nov 16, 2018 at 15:57
  • 1
    \$\begingroup\$ 120-0-120 and 60 A ... that would be 4 generators! \$\endgroup\$
    – gbarry
    Nov 16, 2018 at 16:05
  • \$\begingroup\$ No, you cannot possibly do this, however, there are other options. When I built my first off-grid house, I stupidly bought a 240V water- pump. Initially I bought a generator that had both a 240V and a 120V output. Then, Later I purchased and 120V to 240V auto transformer. outbackpower.com/products/integration-products/auto-transformer \$\endgroup\$ Nov 16, 2018 at 16:50

3 Answers 3


If you want to use one generator on each side of a 120/240 volt, split phase system, you don't need a parallel kit. If you don't want to connect any 240 volt loads, you only need to connect one generator between neutral and one hot leg and the other between neutral and the other hot leg. You need to to do whatever the utility requires to assure that your system is disconnected from the utility when the generators are connected. There must be no possibility that your generators energize the utility lines. You need some kind of transfer switch. In can probably be a manual 2 or 3 pole double-throw switch. You probably should not make any kind of connection involving plugs and receptacles.

  • \$\begingroup\$ This is dangerous as any loads wired for 240V will only receive 120V and could damage the load and even the generator. However, you are spot on about the need for isolation from the utility. \$\endgroup\$ Nov 16, 2018 at 17:03
  • \$\begingroup\$ When the OP wrote "I get that running 220 V can cause phase issues. That’s not what I want to do" I took that as the truth. And I stated: "If you don't want to connect any 240 volt loads" at the preface to what I suggested. I believe the OP knows that connecting 240 volt loads will have a bad result. I think that "dangerous" overstates the problem a bit. If 240 V loads are connected, they certainly will not behave as they are intended, and there is some chance they could be damaged, but I doubt there is a risk to the generator. \$\endgroup\$
    – user80875
    Nov 17, 2018 at 1:18
  • \$\begingroup\$ Electrical panels do not care about intentions. It can be dangerous to power a 240V panel with 240V loads at 120V, period. \$\endgroup\$ Dec 3, 2018 at 16:41

So you situation when connected to the grid is that you have power from the utility coming in on Black-White-Red. Loads at position (a) see 120VAC. Loads at position (b) see 120VAC. Loads at position (c) see 240VAC. Phases stay aligned due to the transformer generating the voltages. All is good.

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Then you want to switch to generators.

enter image description here

The leads from the 2 generators are Black-White and Black-White. Connect the White's together and the Black's to Red and Black as shown. Loads at position (a) see 120VAC. Loads at position (b) see 120VAC. Loads at position (c) see a voltage that is constantly cycling between 0 and 240VAC. The 2 generators are not at the exact same frequency. So as they slip the sum of the two generators will be cycling between in-phase and 180° out of phase. This may be harmful to some loads.

So in summary. It's close. But bad. Don't do it. Sell those 2 120VAC generators and get one that generates 120/240.

  • 2
    \$\begingroup\$ Note to OP: "So as they slip the sum of the two generators will be cycling between in-phase and 180° out of phase." Be very clear about this. The 240 V supply will ramp up and down from 0 to 240 to 0 at a frequency equal to the difference in the two generators. If one is running at 60 Hz and the other at 61.5 Hz the power will will switch on and of 1.5 times per second. I can't think of any load where this would be acceptable. \$\endgroup\$
    – Transistor
    Nov 16, 2018 at 17:31
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    \$\begingroup\$ Are you aware that this site has a built-in schematic editor? \$\endgroup\$
    – brhans
    Nov 16, 2018 at 19:51

The voltage at L1 rises to plus 120 relative to the white neutral at the same time as L2 drops to minus 120 volts relative to the same neutral or center point which is the white neutral.

In order to keep that relationship steady, it is critical that the phases are locked in frequency 180 degrees from one another.

The newer inverter generators use an internal phase locked loop (PLL) so when the generators are paralleled using connecting wires and a common socket for the 120V output. If the PLL was set to keep the two phases 180 out of phase the result could be 240V.

I am just now researching to see if that can be done on Benchmark 4000i invertor generators with parallel kit coupler. If the capacitors are rated for 240V, it would be trivial; otherwise we have to buy 50 ampere autotransformers for ~ $1000.


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