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Electrical question about 3-wire and 4-wire receptacles

Post in 'DIY and General non-hearth advice' started by wahoowad, Feb 17, 2008.

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  1. wahoowad

    wahoowad Minister of Fire

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    I have a 4000W portable generator I want to use to backfeed my house during power outages. It supports both 120 and 240 output. I know this is a smallish generator so I will turn off all breakers, including the main to the street power, and selectively turn on only the minimum circuits I want to power. I'm familiar with the loads my appliances pull and can manage generator load by selectively powering on different circuits.

    I wired my detached garage for 240V. I will plug my 240 output into my 240 receptable and let this backfeed to my main house circuit breaker panel. My understanding is this will energize both 120 volt legs of my house breaker panel. Here is my delimma: My generator's 240 output is a NEMA L14-30 receptable which is a 3-pole 4 wire receptacle. My 240 circuit in my garage was wired to operate a 240V electric heater and has a NEMA 6-30 receptacle, which is 2-pole 3 wire. I could make this work by only wiring up the 2 hot les and the neutral between the generator and my 240 wall outlet, except I lose the ability to have a ground fault on the generator trip the breaker. Right? If this is a bad idea then how come it is OK to plug my electric heater into this?

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  2. sedanman

    sedanman New Member

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    My understanding is that you NEED a transfer switch to do this properly. You are not completely disconnecting your house from the drop by pulling the main breaker. You can still harm a lineman by backfeeding without a transfer switch. You would not want that on your conscience now would you? Call an electrician.
  3. wahoowad

    wahoowad Minister of Fire

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    A transfer switch makes it easier, and often automatic, but it isn't required.
  4. Sandor

    Sandor Minister of Fire

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    Sadenman - your wrong.

    Wahoo,

    I did the same thing with a Generac 4000XL. My only concern was to be able to run the well pump, and the 4k watts is plenty.

    The electricians call them suicide plugs, because you can have a live male plug with the generator running. I made a double male cord that I plug into the 3 prong 240volt receptacle I use for an air compressor.

    On a 3 wire 240v plug the ground wire goes back to neutral on the breaker panel. A 4 wire to 3 wire conversion plug jumps ground and neutral.

    If your paranoid, you can ground the generator. The easiest way I can think of is to make a false cord to plug into another receptacle with only the ground wire.

    Edit: Remember that this is ILLEGAL and potentially DANGEROUS. If you don't understand A/C electric, do NOT EVEN ATTEMPT.
  5. wahoowad

    wahoowad Minister of Fire

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    Has anybody purchased a low cost, basic transfer switch?
  6. Highbeam

    Highbeam Minister of Fire

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    I just did something similar in a legal manner which was approved by my state's inspector just recently. I replaced my entire electrical panel with a UL approved generator transfer panel. The transfer panel has a mechanical interlock device that acts to prevent one double pole breaker in the branch circuit stack from being turned on unless the main breaker is turned off. A little piece of sheet metal does this which can be bought seperately and added to your existing panel. My old panel needed to be replaced anyway so I did it with the generator panel.

    So this one double pole breaker is the "generator" breaker which can be of any amperage. Mine is 30 amps and the 10 gauge, 4 conductor wire leads to a generator plug on the outside of my house. This generator plug is a male plug that matches the typical 30 amp twistlock plug on a portable generator. I bought it at home depot. Now 30 amps of 220 is more than 6000 watts but I use a 3500 watt genset to legally backfeed my house. All legal and inspected. I needed to have a 4 conductor wire to pass inspection.

    The mechanical interlock method is the cheapest and easiest way to do a whole house transfer legally.
  7. Gooserider

    Gooserider Mod Emeritus

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    Note that per codes it is 100% ILLEGAL to back feed a house UNLESS there is a transfer switch or equivalent that will not allow the generator to be connected UNLESS the mains are disconnected.

    This is a serious safety issue as you are putting peoples lives at risk if you backfeed onto the mains by accident.

    Gooserider
  8. SlyFerret

    SlyFerret Minister of Fire

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    Sounds like another Vonage commercial! I can hear the music already!

    -SF
  9. Mr.M2

    Mr.M2 Member

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    A solution I'm working on is to install dedicated outlets in key areas totally separate from the housing electrical system.
    My generator will plug into a a 240 outlet on the outside of my house and power up it's own set of outlets throughout the house.
    Unplug the fridge from the white outlet which is hooked to the panel and simply plug it into the brown outlet next to it which is fed by the generator.
    I only need power for a couple of items and I've done plenty of electrical work to make it a pretty simple task.
    When the power comes back on there is no worry about switching anything. I can take my time and switch things back.

    I've known people who turn off their main breaker, plug the generator into a exterior wall outlet and then try to back feed power to their entire house.
    Most outlets are only 10 or 15 amps and the wire gauge is not sufficient to power the whole house.
  10. sparke

    sparke Minister of Fire

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    Gooderider is correct. Not sure about other states but is illegal in Maine per utility provider. It is also a NEC code violation to backfeed a panel hooked up to a utility without approved safety switch. Several ways to do this. What size is your service? 100 amp or 200 amp? My suggestion may change based on that info. I am a licensed Master Electrician...
  11. Yardbird

    Yardbird Member

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    I found a couple smaller, older battery backups for computers at a used appliance store. I picked them up, and have one behind the couch with a lamp plugged into it, and another in the basement with a lamp. That way, if the power goes out in bad weather, we have about 45 minutes of light. Total cost was 50 bucks.

    Just a thought. Obviously, these aren't enough to run any appliance, but for lights, they work well. It keeps the kids calm.
  12. Gooserider

    Gooserider Mod Emeritus

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    Not a bad idea, but there are a few "gotchas" that you might want to watch out for, and test to make sure you aren't going to have trouble with them...

    1. Many units will NOT start up if they don't have AC power being drawn from them at some minimum level when the power goes out - IOW, if the light isn't on when the power fails with the light not on, it won't work when you turn the light on... Or if you turn the light out after the power fails (say to extend the time), it won't restart. The fix is to have some minimum constant load on the unit at all time, like a night light or a low power "phantom load" appliance like a VCR. How much load is needed varies, you'll need to experiment.

    2. The main reason these units end up in 2nd hand shops is that the batteries in them tend to get tired after a while, and won't deliver their rated capacity - resulting in shorter than expected run-times. The batteries ARE replaceable fairly easily if you are reasonably clueful about working on the insides of appliances and such - just be wary of the large capacitors you will also see in the units, they can pack a wallop even when disconnected. The batteries are sealed lead acid "gel-cells" which come in standard sizes, however what size and how many vary from unit to unit - it's a case of open it up and see what's inside.

    3. I haven't personally experienced this, but I've heard that some UPS outputs don't mix well with Compact Flourescent light bulbs, or other low energy lighting - test before your moment of need...

    The other key factor in determining run-time is the amount of power draw - use the smallest bulb you can get by with - a 25 watt appliance bulb will supply enough light to see by, and run 2-3 times longer than a 100watt bulb (the run-time <> Power draw relationship isn't linear)

    Gooserider
  13. Highbeam

    Highbeam Minister of Fire

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    "I’ve known people who turn off their main breaker, plug the generator into a exterior wall outlet and then try to back feed power to their entire house.
    Most outlets are only 10 or 15 amps and the wire gauge is not sufficient to power the whole house."

    This is fine. The breaker on the branch circuit protects the wire from passing excessive current. Only half of his circuits will be backfed this way since you are only backfeeding one side of the panel.
  14. Gooserider

    Gooserider Mod Emeritus

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    Technically it is fine, it is also ILLEGAL in most states - backfeeding is not legal if it is POSSIBLE to have the backfed current reach the street - which could easily happen if one forgets to disconnect the mains breaker... Reason being the potential hazard to the line workers attempting to restore power.

    Gooserider
  15. colebrookman

    colebrookman Minister of Fire

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    Potential hazard not only to line workers but also to firemen and other first responders who are working around downed lines that they were told were de- energzed by the power co. Think lawyers, law suits, good by house and future income.
  16. wire_twister

    wire_twister New Member

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    Never good to run anything wiyhout a ground, especially during the time a higher voltage line could be brought down across the ones going to your house, with no ground the damage to your house will be tremendous.

    As far as why it is OK to run your heater on a NEMA6-30 plug it is because the heater is a purely 240 volt load(does not require a neutural to work) and therefore only needs 3 wires, 2 hot and a ground.

    The dedicated generator system will work, but a transfer switch will be much less trouble, as far as backfeeding DO NOT DO IT, it is better to sit in the dark and pay for new food if it spoils than to try to pay for a life you might take by accident.
  17. bruce

    bruce Member

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    dont be stupid , the cheap come out expensive, buy a transfer switch for 300 or less and be safe! dont mess around and try to con the insurance to pay for a fire that could have been avoided
    i used my switch saterday night in the wind, transformer blew , my lights back on in 7 min, power back on later fliped the switches back and on we go!
  18. seige101

    seige101 Minister of Fire

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    I must echo what everyone else has said, backfeeding a house from a generator without a transfer switch is highly illegal, against electrical code and unsafe. Besides all the issues stated before, if the utility power gets turned on while the generator is backfeeding you will have your own private fireworks show with the generator and the wiring in your house.

    Spend the 300 bucks go to home depot, they sell a kit for about 300 bucks with everything needed to safely wire a generator into a house panel.
  19. Ken45

    Ken45 Minister of Fire

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    The other cheap and safe alternative is just to run a heavy line from the generator to the inside of the house and have enough heavy duty extension cords to reach what you really need. That's less costly than a transfer switch. How many items do you really need to power during an outage? In our case, it's maybe the refrigerator and a couple of lights. Maybe the blower on the stove. Last time we had a power outage, I didn't even bother with the generator.

    I'm not against the proper transfer switches. I'm just pointing out a cheap, safe alternative to those who don't want to pay for a transfer switch and installation.

    Ken
  20. d.n.f.

    d.n.f. New Member

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    I just run the generator with extension cords going to my deep freezer/fridge and maybe to the tv.
  21. wahoowad

    wahoowad Minister of Fire

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    Thanks for all the advice about code! Now, back to the original question...
  22. Gooserider

    Gooserider Mod Emeritus

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    Agreed in theory, but you might want to find out what an electrician will charge to install the kit, or if they will install your kit rather than supplying their own -

    Bear in mind that this is NOT a job to be tackled lightly as it is an inherently high-risk job - you will be messing with the HOT side of your electrical panel, with NO breaker between you and the street - IOW, high voltage, high current potential wiring, with no easy disconnect, unless possibly you are able to pull the meter, something the utilities will frown on in many places....

    I do a fair bit of electrical work, about as much as a non-licensed person can do quasi-legally, and I would hesitate to tackle this kind of job... I would put installing a transfer switch in the same general category as dropping a tree that is overhanging and leaning towards your house - NOT something to be tackled w/o having the right equipment and knowing EXACTLY how to use it...

    Gooserider
  23. seige101

    seige101 Minister of Fire

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    Any decent electrician should be able to install customer supplied parts, unless they just want to sell you their kit or method so they can make the markup on materials.

    You are correct this is not the job for the average homeowner, but is able to be tackled by someone who is a competent handy man type person.

    I understand your concerns with being able to completely turn off the panel. This kit is not a true transfer switch, you simple take the existing wires off the breakers splice them into a pre-made wiring harness that goes to this individual transfer switch and then from there back to the original breaker. This kit essentially is a dual selector switch for your individual circuits you want to be able to have backup power, you manually switch the circuits over with a switch from utility power to to generator power. At the same time preventing backfeeding issues.

    However maybe i am biased because i am about to obtain my electrical license in the near future.
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