Can it be done with 120v

Hi
I was having a discussion with a friend. Hes telling me that you can use a portable generator that has only a 120v 30a output (TT-30-R) to feed both phases of a single phase breaker panel and that all 2pole equipment fed from that panel will work. AC that uses a 2pole 20amp receptacle and/or a hot water heater that is wired for 2pole 30amp. I said NO. He says YES.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Uh no. How does a piece of equipment that needs 240 volts to run run on only 120 volts? Also the voltage between the two 240 volt conductor will be zero volts so even if it could run on 120 volts it won't run.
 

FionaZuppa

Senior Member
Location
AZ
A "2pole" recept? Doesnt that suggest a MWBC or just two BC's, of which you can get 240v by connecting device L-L line to each L of each recept? Not sure how you could get 30A though unless it was a dual recept rated for 30A, etc.
 

480sparky

Senior Member
Location
Iowegia
If feeding a 120v - to - ground circuit to a 240v load will work if you run the 120 volts through both poles of a 2-pole breaker, then hooking the 120v conductor to both terminals of the 240 load will work the same. Then you'd only need a 1-pole breaker. :cool:
 

480sparky

Senior Member
Location
Iowegia
The claim is you can run a 240 load off a 120v source by applying the 120 to the two lugs of a panel, then installing a 2-pole breaker.

If that works, it doesn't matter where you connect the 120v source to the 240 load... panel or load. Electrically, it's the same result. Nothing will work as you have 0 volts at the load.
 

FionaZuppa

Senior Member
Location
AZ
The claim is you can run a 240 load off a 120v source by applying the 120 to the two lugs of a panel, then installing a 2-pole breaker.

If that works, it doesn't matter where you connect the 120v source to the 240 load... panel or load. Electrically, it's the same result. Nothing will work as you have 0 volts at the load.
I believe everyone here knows this already....... and not directed at anyone.......
If the supply/source is only 120v, then that's all there can be.
240v CT has two ends, many call them "poles" that are "phase shifted" w/ ref to center (which of course they are not, it's all one/same phase), but if you take -120v from one side and connect that to a ckt where the other side is +120v, the diff is 240v, not zero. |-120 - 120|=240
It is not |120 - 120| pole-to-pole, etc.

Or, I perhaps am not understanding the general question.
 

tortuga

Senior Member
Location
(44.057116, -123.103394)
Occupation
field supervisor
Hi
I was having a discussion with a friend. Hes telling me that you can use a portable generator that has only a 120v 30a output (TT-30-R) to feed both phases of a single phase breaker panel and that all 2pole equipment fed from that panel will work. AC that uses a 2pole 20amp receptacle and/or a hot water heater that is wired for 2pole 30amp. I said NO. He says YES.
My old co-worker does this and we had a similar discussion one time its a great reminder of ohms law. He has a huge 120V generator, I have no idea why but it is 120 only.
A standard 50 gallon resistance electric water heater typically has a 4500 watt element. Thats 12.8 Ohms. At 240 V it pulls 18.75 amps and produces the 4.5kW of heat.
When he has a power outage he wires it to a 15A 120V breaker 120V/12.8Ohms = 9.4 Amps or 1125W. It takes a lot longer to heat up but his wife eventually gets a warm shower.
There is no way this would work for a motor obviously.
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
My old co-worker does this and we had a similar discussion one time its a great reminder of ohms law. He has a huge 120V generator, I have no idea why but it is 120 only.
A standard 50 gallon resistance electric water heater typically has a 4500 watt element. Thats 12.8 Ohms. At 240 V it pulls 18.75 amps and produces the 4.5kW of heat.
When he has a power outage he wires it to a 15A 120V breaker 120V/12.8Ohms = 9.4 Amps or 1125W. It takes a lot longer to heat up but his wife eventually gets a warm shower.
There is no way this would work for a motor obviously.
That would only work if he has a power outage on only one side of the split phase, that rarely happens.
 

GoldDigger

Moderator
Staff member
My old co-worker does this and we had a similar discussion one time its a great reminder of ohms law. He has a huge 120V generator, I have no idea why but it is 120 only.
A standard 50 gallon resistance electric water heater typically has a 4500 watt element. Thats 12.8 Ohms. At 240 V it pulls 18.75 amps and produces the 4.5kW of heat.
When he has a power outage he wires it to a 15A 120V breaker 120V/12.8Ohms = 9.4 Amps or 1125W. It takes a lot longer to heat up but his wife eventually gets a warm shower.
There is no way this would work for a motor obviously.
"Wires it to a single 120V breaker." meaning he connects the other pole to the neutral, I assume?
 
Top