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  1. #1
    Arapaima Dan F's Avatar
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    Q's about Back-feeding Electricity from Generator

    We're going on hour 6 of a power outage and it sounds like it may be a while.

    I have two generators, a 5000W generator on wheels plus a 6000W Onan unit in our RV. In the past I have run messes of cords through the house. This is a real pain, plus I have to leave the door to the garage cracked open..

    A friend told me about back-feeding the service through a plug, so I thought I would give it a try.

    Before starting I shut off the service disconnect.

    I made up a male-male adapter. I attached this to a 100' 12 gauge extension cord. I plugged the male end of the extension cord into an outlet and the female into my adapter (a plug off a power tool with a male adapter on it). It is very important to plug into the generator last, a live male end is a dangerous thing!

    I tried going through an outdoor plug first. That only energized the circuit I plugged it into. The culprit turned out to be a GFCI that would pop as soon as I tried back-feeding.

    Next I plugged it into a dedicated freezer plug (freezer not in use). This worked, but only with half of the circuits...

    My thinking is that I only energized half the circuit board because of the 120V breakers.

    The generator has a 240V outlet, but it is a twist-lock connection, which I do not have. When the hardware store opens I'm going to get the parts, then I can hook it up 240V. This will also get me twice the wattage out of my 12G cord.

    Does anyone know if this will solve the problem?

    If other people have different methods of hooking up their home service to a generator, please reply, as I think others may be encountering similar problems.

    Please, no "Call a licensed electrician" replies, this is the DIY section.
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  2. #2
    Redtailed Catfish Jgray152's Avatar
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    First, don't use extension cords. They are rated from 10-15 amps and a 5000watt gen is about 41 amps.

    You never want to back feed the panel through an outlet. First, the outlets can only hold up to 15 amps of power. Also, some outlets may only be wired with 14 gauge wire, not enough to fed a panel.

    Tell ya what, go to the store, buy your self atleast 25' of 12/3 wire. 10/3 is better but 12/3 will work if you can't find 10/3.

    12/3 means you have 3 wires (not including ground) which are 12 Gauge. Same goes for 10/3. The lower the number, the thicker the wire.

    The 4 prong connector on your generator is for 240 volts. Watch out though, there are two different 240 v connectors. They look EXACTLY the same but one has a small tab on one of the pins facing out of the circle of prongs and the other has the tab facing into the circle.

    To figure out which you need,
    L14-20: 20 Amp 240v plug. Tab facing out of circle.
    L14-30: 30 Amp 240v plug. Tab facing in the circle.

    If you look on the 240v recepticle, it will say what type of plug it is. It will either say L14-20 or L14-30. The brand name will probubly be NEMA.

    12/3 wire has 4 wires.
    1 Red (HOT)
    1 Black (HOT)
    1 White (Neutral)
    1 Copper (Ground)

    On the back of the plug you will see some letters. GWXY. These are very important.

    G - Ground
    W - Neutral
    Y - HOT
    w - HOT

    It doesn't matter which HOT wire goes to which letter but make sure you have the Neutral and Ground wires correct.

    After you wire up the plug, you will then need to wire the panel.

    TURN MAIN OFF!!!!!! Also Turn off all other breakers as well.

    With the main off you are safe. Even if you don't have power, you don't knowif the power company is just about to hook you back up, or if someone is backfeeding the pole wires with their generator. All are bad news for you.

    Find a 240 Breaker. They are one of the double breakers. Usually people, like me, will back feed into a dryer breaker, obveously the dryer will be disconnected.

    Remove the Circuit Panel cover. Find one of those 240 breakers and disconnect the wires from it, wrap up those disconnect wires and push them to the side. You don't have to remember the order of the wires on the breaker.

    See if you can run your 12/3 wire through an open port in the panel on its side. If not, its not a big deal, you just won't be able to put the panel cover back on correctly.

    Now, strip back the outside insulation about 12-18". Strip the ends of the White, Red and Black Wires.

    Connect the White and Copper (Ground) wire to the ground strip inside the panel. You will find white and copper wires connecting to it. Neutral and Ground are the same.

    Connect your Red and Black wires to that 240v double breaker which in my case was the dryer breaker. Again, it doesn't matter what order you connect the red and black wires to the breaker in.

    Make sure all your connections are solid and there there are no bare wires that could cause issues.

    Start up the generator atleast 10' or so away from the house with the exhaust pointing away from the building. I would reccomend not putting it in the garage. It will not hurt the gen to have snow fall on it. TRUST ME. For your own safty!!!

    After the Gen has warmed up for about 5 minutes. Plug in the 12/3 wire to the Gen into the 240v recepticle. Make sure the breaker you are using for the GEN is OFF.

    After noticing there are no sparks flying. hehe. Go inside the panel and turn on the GEN breaker. Then turn on each breaker one by one. The best one to start would be the breaker for the basement or where the panel is so you can have light.

    Hope this helps.
    Last edited by Jgray152; 12-21-2008 at 12:07 PM.
    RIP Jack - 10" Jack Dempsey (2006 - Sep 26 2012)



  3. #3
    Cobra Snakehead
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    The good way to do it is install a sub panel with a manual throw switch. The manual throw disconnects the primary service and switches it to the generator. This is pretty much code.
    Your power is 240 single phase. One service lead provides power to the left side of your breaker box, the other lead provides power to the right side. If you want, you can redo your breakers so you only need to provide power to one side of the box to power your necessary items.

    I used 6AWG, 3 conductor with a ground. I used female - female to female cable. I provide two 30 AMP legs to my sub panel. I have the fridge, TV (with antenna), microwave, some lights, all of the fish stuff, and a couple convenience outlets.


    Pushing power back into your house over a standard wall outlet isn't the best method, but it can work in a pinch. You just need to wire in a breaker at the maximum rating of your cable, that feeds back into your house. If you are running it through a 14 AWG then put a 15 amp breaker between the generator and plug. 12 AWG gets you 20 AMP. You need to remember that constant load should only be 70 percent of the breakers rated capacity. If you have a 15 amp breaker then you shouldn't put a continuous demand of more than 12 amps on it.

    You also have to make sure that you have a failsafe method to disconnect the service, otherwise you can kill a lineman who is standing at a pole down the road. At the least you can get a hefty fine.
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  4. #4
    Redtailed Catfish Jgray152's Avatar
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    BTW, if you wire through an outlet, you will not be able to run high loads such as a well pump, furnace (sometimes high loads), Electric heat of any kind, etc.

    Like the poster above said, installing a sub panel would be better more permanent way of doing it. In a quick pinch though, running without installing a sub panel will be fine. After you get power back, I would get someone in to have the panel installed for you.

    This is the real right way to do it.
    http://www.gen-tran.com/
    RIP Jack - 10" Jack Dempsey (2006 - Sep 26 2012)



  5. #5
    Smallmouth Bass Buckdog's Avatar
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    That was excellent. I'm printing out this thread and keeping it. I didnt know Grainger carried transfer switches like that but I'm definitely going to look into them now.
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  6. #6
    Arapaima Dan F's Avatar
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    Thanks Jgray!

    I wrote that thread and then went to town to get the male plug. It's a good thing I took a picture of it to take with, there really are a lot of different configurations!

    When I got back, I had no idea what wires to hook where- I was hoping to back-feed through a 240V plug that is only two flat prongs and a round ground.

    Your response was very helpful! I had a 40' piece of 8/3 wire in my barn and it is powering everything but the heat and the well without a problem. From the looks of things this may be a very outage (at least by our standards), at least 24 hours, maybe more...
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  7. #7
    Great Barracuda crisper's Avatar
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    Yes a transfer switch is required by code. This way only the generator or the utility power can be feeding your panel at one time. Two seperate sources of power can not be feeding one load at the same time. This will create a dead short across your mains.



  8. #8
    Bullshark Knowdafish's Avatar
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    Quote Originally Posted by crisper;2560872;
    Yes a transfer switch is required by code. This way only the generator or the utility power can be feeding your panel at one time. Two seperate sources of power can not be feeding one load at the same time. This will create a dead short across your mains.
    Yup! That's what they use in a R.V. to switch between outside power and the generator. A 50A transfer switch would be the hot ticket! You can also get an automatic start for the generator too (as long as your generator isn't rope start!!) which cranks up the generator when your main power goes out. That way you don't even have to be home and the whole thing is automatic!!! Be sure and use a minimum of 8 gauge wire. If you're using 6 Ga. even better! Make sure the generator is grounded to your breaker panel, any sub-panels, and the transfer switch if you decide to use one. Be careful and think everything out before firing it up! Screw up bad enough and this is a very good way to burn a house down!! Good luck!
    Originally Posted by knifegill Well, that settles it. I'm moving to the Philippines.
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  9. #9
    Cobra Snakehead
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    Or if you have the cash get one of these guys Standby Generator



  10. #10
    Redtailed Catfish Jgray152's Avatar
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    I wrote that thread and then went to town to get the male plug. It's a good thing I took a picture of it to take with, there really are a lot of different configurations!

    When I got back, I had no idea what wires to hook where- I was hoping to back-feed through a 240V plug that is only two flat prongs and a round ground.

    Your response was very helpful! I had a 40' piece of 8/3 wire in my barn and it is powering everything but the heat and the well without a problem. From the looks of things this may be a very outage (at least by our standards), at least 24 hours, maybe more...
    Yup you have the 20 amp recepticle.

    You should be able to run your heat and your well. Especially with 8/3. If you were going to run either of those, especially the well pump, just make sure you have minimal things powered. The surge from the well pump can be 3 times as much as its rated continuous power.

    I was looking over a house with a 5200 watt generator head powered by a 10hp motor. Their well pump would strain the gen after some time. It seems after the Gen head got warmed up this would happen. Otherwise the gen would handle the load fine.

    When a generator head heats up, its efficiency goes down. Heat aids in resistance to power.

    A 5200 watt gen head, according to math, needs a 8.22hp engine. That is if the gen head is operating at 100% efficiency which no gen or alt head can do when converating mechanical energy to electrical energy. Lets say the Gen head is 80% efficient. That means the engine would need to have enough power to spin a 6240 watt gen head which means you would need 9.80 hp. That is without the heat resistance

    A 10 hp engine may just work with small loads but it doesn't have enough over head power to compensate for the added mechanical resistance when the gen head heats up.

    11-12 hp would have been better on the Generator that I was baby sitting for. O well.

    That may have been some usless talk right there but it got me thinking....out loud... lol. I suppose it may help when picking out an efficient generator with the correct gen head / motor combination.

    to find out how much HP you would roughly need for a specific wattage.

    Wattage / 745.7 * 1.18 = Engine HP

    An equation I used during the past few years telling people how much HP is lost or gained with an electric fan for the cooling system.
    Last edited by Jgray152; 12-21-2008 at 11:37 PM.
    RIP Jack - 10" Jack Dempsey (2006 - Sep 26 2012)



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