120V generator to power a residential 240V panel

[jjhoward]

Happy New Year!
I have a customer with a small 3000 watt inverter generator (intended for camping). At the customer's home, we installed a listed mehanical interlock for his GE 200 amp main breaker panel, a 240V-30 amp generator breaker and a 240V-30 generator inlet port.
I have a standard 4 wire generator cable (L14-30P on one end, a L1430-R on the other end).
I have also procured an adapter cable that mates with the L14-30P end of the generator cable and the other end is a TT-30P that will mate with the customer's generator.
So, the 2 hots in the 4-wire generator cable (X & Y) will be tied together once this adapter cable is attached. There will be 120V from each "hot" in the 4-wire generator cable to neutral once the cables are attached to the 120V generator. The ground in the TT-30P is connected to the ground lug in the gen cable.
Can this 120V connection to the 4-wire gen cable be damaging or dangerous to any loads in the residential panel??
I pondered this for some time...I don't see a problem, but I would like to hear from the great minds here before I do something DUMB!!
Thank you.

 

[Buck Parrish]

Have you put your meter on it to see if you're getting 240 from both hots.?

 

[rambojoe]

If you don't see a problem, then don't do it.

 

[tom baker]

What will happen with 240 v loads?

 

[synchro]

Can this 120V connection to the 4-wire gen cable be damaging or dangerous to any loads in the residential panel??

It should not damage any loads, but it's possible under worst case conditions that the neutral conductor of a MWBC could be overloaded. For example, it their was 12.5A on each leg of a 3-wire MWBC then there'd be 25A on the neutral because the currents add in-phase instead of subtracting. If there are no MWBCs then I don't see any risk of damage.

 

[winnie]

Any 240V load would not get power.

Any 120V load would function.

Any multiwire branch circuit would risk having an overloaded neutral, however with only a 3000W generator this is unlikely to be a problem.

-Jon

 

[Buck Parrish]

Okay I miss read the part where you're tying the two 120s together. It should work as long as the 240 volt breakers in the house panel are off. If I'm following you.
But personally , I would not do it.
With all the Led's, smart switches, smart appliances and computers. It's hard enough to keep every thing functioning correctly with clean power.

 

[ptonsparky]

It is what I have at my house. They make a short adapter cord for the purpose.

 

[Hv&Lv]

As stated before, MWBC maybe.. but its a 25 amp generator. lights, refrigerator and a few outlets with something plugged in will about be it. Your not going to run heat strips, stove, or anything like that.
Maybe a well pump if nothing else is running.

 

[jjhoward]

Yup, the MWBC can certainly be overloaded since there isn't any canceling current happening. 3000 watts at 120V is 25 amps, theoretically enough to overload either a 15 amp or 20 amp MWBC. I will check his panel for split circuits.

 

[retirede]

Okay I miss read the part where you're tying the two 120s together. It should work as long as the 240 volt breakers in the house panel are off.

Why do they need to be off? If you measure the voltage on the load side pole to pole, it will be zero. On or off.

 

[jjhoward]

Yes sir. No potential between leg A-B. They are tied together. However, I am sure some 240V appliances may pull current through 1 leg for control etc. So those parts of 240V appliances will work (if they are there).

 

[jjhoward]

Have you put your meter on it to see if you're getting 240 from both hots.?

No 240V anywhere. There is only 120V coming in at the TT-30P 3 wire connector (Hot, neutral & grnd). In the 4-wire cable both hots are tied together & are connected to the 120V hot at the TT-30P connector. The neutral from the 3 wire connetor is conneceted to the neutral of the 4 wire grnd is connected to grnd.

 

[Little Bill]

I just did one just like this a month ago. I instructed the customer and even put instructions on the panel to never turn on the 30A generator breaker with the cover off and Utility power on. It has an interlock but wouldn't do any good with the cover off. I don't think the customer would ever have the cover off but I warned him and put up the instruction sheet for anyone else that might not know. Also told them to call me or another electrician if they ever sell the house so that it can be disconnected.

 

[kwired]

Yes sir. No potential between leg A-B. They are tied together. However, I am sure some 240V appliances may pull current through 1 leg for control etc. So those parts of 240V appliances will work (if they are there).

Many electric clothes dryers would power any controls and the 120 volt motor, but no potential across the 240 volt heating element means it will not heat.

Electric water heater- no potential across 240 volt element= no heat.

Worse yet is to only power one bus in the panel and leave 240 volt breakers on while doing so. Any 240 volt load that is "on" will let current through from your energized pole and put that load in series with everything connected to the other panel bus. Water heater cool enough to call for heat does it every time even if no other 240 volt appliances are "ON".

 

[tag58]

Similar setup -- I understand what has been written in questions/replies above, but my 120vac (only) inverter generator output is 60vac between either pole and ground (receptacle grounds and generator frame are bonded). Generator single line diagram (all that's available from Ryobi, and only after asking) shows outlet grounds only tied to generator frame, not back to the inverter. Is 60vac what I should expect from a floating ground on a 120v inverter generator (if so I will bond the (normally considered) neutral side of the 120v output to ground at my home's panel), or is this indicating that Ryobi has an internal common reference point (60v) to the power transistors of the inverter tied to the receptacle grounds?

If Ryobi has connected the output receptacle grounds of this generator back to the inverter, then I don't want to risk shorting one side of the output to ground (by bonding at my panel). But since Ryobi is not able to provide an output wiring schematic, and I have no experience with a 120v only inverter generator, then maybe I just don't understand how the output of these inverter generators are normally wired up?

 

[ptonsparky]

Similar setup -- I understand what has been written in questions/replies above, but my 120vac (only) inverter generator output is 60vac between either pole and ground (receptacle grounds and generator frame are bonded). Generator single line diagram (all that's available from Ryobi, and only after asking) shows outlet grounds only tied to generator frame, not back to the inverter. Is 60vac what I should expect from a floating ground on a 120v inverter generator (if so I will bond the (normally considered) neutral side of the 120v output to ground at my home's panel), or is this indicating that Ryobi has an internal common reference point (60v) to the power transistors of the inverter tied to the receptacle grounds?

If Ryobi has connected the output receptacle grounds of this generator back to the inverter, then I don't want to risk shorting one side of the output to ground (by bonding at my panel). But since Ryobi is not able to provide an output wiring schematic, and I have no experience with a 120v only inverter generator, then maybe I just don't understand how the output of these inverter generators are normally wired up?

My inverter generators are the same way. Even my old generator was 60v to ground at generator.
Neutral (not the right term), white wire and EG, green wire, bond at the the transfer switch.

 

[rnatalie]

Some of the little generators (Honda specifically) have an option to gang two of them together to make 120/240 power.

 

[ptonsparky]

Some of the little generators (Honda specifically) have an option to gang two of them together to make 120/240 power.

Mine don't make 120/240. They just give me increased power at 120.

 

[Little Bill]

Mine don't make 120/240. They just give me increased power at 120.

Same with two that I just installed an inlet for.