120v Generator to power a home

Discussion in 'Electrical Forum discussion & Blog' started by crabjoe, Apr 21, 2020.

  1. crabjoe

    crabjoe New Member

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    I hope someone can answer some questions for, in regards to using a generator that's normally used to power RVs.

    RVs are setup for 120v, usually 30 amps. They usually use TT-30.

    Let's say the house has a L14-30 for the connection. Because of this, an adapter (TT-30p to L14-30r) will be needed and the two hots on the L14-30r will be bridged. It'll be connected to the home using an interlock, so both legs of the service panel will be hot.

    Questions:
    1. if no breakers are turned off, what might happen to anything that's on a 240 breaker? Remember, both legs of the panel will be hot, but they will NOT be 180 from each other.
    2. If one were to leave a 240 electric water heater on, will it still heat, just slower?
    3. Outside of possible issues with 240, might there be any other issue?
    4. What happens to motors, such as a well pump, that are 120/240, when it sees both hots are in phase?

    Thanks!
     
  2. LLigetfa

    LLigetfa DIYer, not in the trades

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    Nothing 240V will work. Any split outlets sharing a common return run the risk of catching fire.
     
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  4. crabjoe

    crabjoe New Member

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    Ok.. does that also mean that it won't go boom or possibly break my 240 appliances like the HVAC or hot water heater?

    Is a split outlet what is also known as a multiwire branch circuit? The ones on double pole breakers as if they were 240 circuits?

    I wonder how many people are feeding their homes with with a 120 generator, using an adapter with a transfer switch of some type doing this? I'm very likely to do this but I'm a bit afraid if I'm not home and someone else does it, they might not know to turn off the 240 circuits.

    Pertaining to water heaters.. Wouldn't something like that still partially work, since it's not a motor but an element that's getting hot from the electric?

    Thanks!
     
  5. Stuff

    Stuff Well-Known Member

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    Most 240vac devices won't even power up. Water heaters get power from hot to hot so won't work at all. Motors designed for residential use same thing. Even if marked 120/240 usually you wire them for one or the other.

    Some dryers and ranges will randomly have the controls work as that part is on one 120v leg but the heating elements will be dead.

    Correct about the split outlets/multi-wire branch circuits. Issue is the neutral wire gets current from both legs so can overheat.
     
  6. crabjoe

    crabjoe New Member

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    Thank you.
     
  7. DonL

    DonL Jack of all trades Master of one

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    Sounds like a formula to produce smoke. :eek:
     
  8. crabjoe

    crabjoe New Member

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    I think it'll be good since MWBC's should be on a double pole, the plan is to switch them off. And even if a MEBC wasn't turned off, unless someone was using both receptacles of a duplex, the neutral should still be fine. The problem with the MWBC would only happen, say if a disposal and dishware were on the same outlet and someone used both at the same time.

    My worry isn't me, it's that someone else in the house might not know what they're doing.. and most of that seems to be a none issue since both legs would be on the same phase... which should make the appliances on the 240v circuits not even power up because they're going to see zero or close to zero volts. At least that's my current understanding.
     
  9. Stuff

    Stuff Well-Known Member

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    The NEC and other codes have a lot in them to handle "it's that someone else in the house might not know what they're doing." This means when a fire does start it is usually not from one thing, but multiple failures/code violations. Remember that anything you do needs to be safe once you walk away.
     
  10. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    I know this is late to the party, but...

    The power company essentially supplies 240vac to the home. The 120vac you tend to use in the USA is sort of an artifact...it's not actually being supplied directly, it's essentially tapped off as half of the 240vac out of the transformer. So, anything you do to a 240vac supply with trying to feed 120vac into it has lots of pitfalls. The phase from one side of the 240vac to the other is opposite, which is why current flows. Applying the same thing to both sides of a 240vac device means there's no voltage difference from one side to the other...if you were to put a meter on it, it would read zero (but 120vac to ground). Phasing in power can be confusing, but if you think of voltage as pressure...applying the same voltage to both sides of a circuit means there's no 'pressure' between the two points, so no power or work can be accomplished. On a shared neutral circuit, pushing the same phase into both 'hots' would mean that they don't cancel in the neutral, so it would carry double what it was designed for...a recipe for failure.
     
  11. kevin Crawford

    kevin Crawford EZ Generator Switch

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    If you want to power from your RV generator thats fine... there are no short cuts or magic that you can create. Your 120 volt RV generator should be tested to see if it is Floating or Bonded neutral first so we know how to make the correct connections. Next we need to take into consideration what load you are attempting to power. Give us that info and I can direct you as to what your options can be!
     
  12. DonL

    DonL Jack of all trades Master of one

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    Generators with 120 Volt outlets are for temporary use, And should be operated using a proper extension cord.

    Buy a whole house generator and do it right, If you feal the need to back feed 240 V.

    Silly ideas normally do not work out very well. :rolleyes: You could end up temporary. :eek:
     
  13. WorthFlorida

    WorthFlorida The wife is still training me.

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    What you are describing are shortcuts and do not want to spend much money? I have said it many times here, If you make a plumbing mistake you get water on your head, make a electrical mistake and you get electrocution and death. An RV generator is designed for the RV environment and all is hooked up to code and for safety. Trying to transfer that for a home is not a good idea. No one on this forum should recommend anything else. Too many die from generator electrocution and CO poisoning. A few here have describe how things work but not that anyone would endorse what you are trying to do. When people here post questions like these, I read that the person is not sure and should not be doing electrical work. FYI, the water heater will not work on 120v because of the thermostats.

    Living in Florida for 30 years it is amazing what people will do with a generator, especially after a hurricane. To do is safely you get a whole house generator such as Kohler (not a portable), an auto transfer switch, permitted and inspected. The only other way is a portable generator running at least 20 feet away from any window or garage and use the proper size extension cords and grounding.
     
    Last edited: May 14, 2020
    HudsonDIY likes this.
  14. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    If you were to put 120vac on one of hot leads in the panel, and the neutral on the neutral, and say that same 120vac on the other hot lead, that would put exactly zero volts into your water heater, as there is no neutral there. So none of the 240vac devices would work, and if there were any shared neutral devices, you'd overload the neutral since the phases will add, not subtract.

    It sounds like you really don't understand this stuff. That is a really good way to really damage things, potentially yourself and your property.
     
  15. Bannerman

    Bannerman Well-Known Member

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    There are small, manually operated transfer switches that would allow the generator to power only specific 120 volt circuits which you would choose at the time of installation.

    If the generator has only 30 amp capacity, that will be equivalent to a maximum of 2-15 amp 120 volt circuits which will likely be sufficient to run a gas or oil furnace and maybe 1 fridge and a few lights. Forget air conditioning, clothes dryer, electric WH and other 240volt appliances as a 120 volt generator cannot power 240 volt devices.

    A transfer switch will ensure no power can be mistakenly sent in reverse into the power grid which could result in disaster for hydro crews working on a distribution system they deemed to be dead. To ensure there can be no backfeed when a generator is temporarily feeding into the home's electrical system, the electrical system must be electrically isolated from the grid, including the neutral connection. A transfer switch will disconnect not only the hot feed(s) but also the neutral.

    In most standalone portable generators, the neutral feed will be 'floating' as there will be no bond to ground. When using a portable generator to temporarily supply power to home circuits, the neutral will typically bond to ground within the transfer switch, and the generator will also be grounded utilizing the same common ground connection point as the home's electrical system.
     
    Last edited: Jun 12, 2020
  16. WorthFlorida

    WorthFlorida The wife is still training me.

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    https://www.foxnews.com/us/family-of-five-dead-from-carbon-monoxide-poisoning-in-louisiana
     
  17. DonL

    DonL Jack of all trades Master of one

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  18. WorthFlorida

    WorthFlorida The wife is still training me.

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    True, and after Hurricane Frances in 2004, my neighbor (around midnight), noticed a truck going slow and occasional stopping listening for a running generator. The back of his truck had a load of generators. When this person saw my neighbor he boogie out in a hurry. But they'll steel them right out of your garage if given the opportunity.

    I have a long heavy duty cable six or eight feet long and a lock when I had to use mine, I loop the cable around a tree or a metal post, even a street light if there is one close enough.
     
    DonL likes this.
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