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Is there a safe way to power my house using a portable generator? The power rating for the generator is 6kW, and I want to run my electric water heater (4.5kW) and my refrigerator (0.5kW) and possibly a few lights.

The water heater is the main priority, but it's wired directly to the house so I can't just unplug an outlet and plug it into the generator.

The method I've heard used most often is to backfeed into the dryer outlet after turning off the main breaker. I'm aware that if I don't turn off the main breaker, I could shock a worker or destroy the generator when the power comes pack on. I also know enough that I have to use a power line rated for the Amperage I'll be drawing. Are there any other dangers I need to look out for?

I had a friend suggest that I deactivate one of the heating elements and thereby reduce the amount of power that the water heater will draw. I'm guessing I'd still need 240V rather than 120, but I'm not sure. It would be awesome if I could just use a 12 or 14 gauge extension cord instead of a really expensive 10 gauge, but I don't want to do anything that will catch my house on fire.

Also, can anyone give me a detailed explanation of steps I need to take for this whole process?

(Any advice would be greatly appreciated. It's been eight days since we've been without power, and possibly 3-4 more until it's restored.)

  • 7
    Here's a really good list of the dangers of doing this: qsl.net/kc5qhh/backfeeddangers.pdf – gregmac May 5 '11 at 21:33
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    WHERE ARE THE DIRE WARNINGS in the answers here against doing this? NEC requires you use a transfer kit/interlock to abolutely ensure you can't feed power back onto the grid (amplified to 17,000 volts or so by going backwards through your transformer, by the way). This seems to be a much better answer. – Craig Nov 28 '14 at 20:47
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    I second that. No one answered the part of his question about what other dangers there are. Everyone keeps talking about backfeeding power, but with the main breaker off this is NOT the biggest danger. There are many dangers, but the biggest one is that the guage of wire isn't sufficient from the drier plug to the panel and that wire will slowly heat up and eventually catch the house on fire. – pilavdzice Oct 6 '17 at 18:26
  • It’s possible, but immoral: the linesman’s life shouldn’t depend on you remembering to properly disconnect the generator. – user1512321 Feb 26 at 4:44
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What you are suggesting with a back-feed cord is possible, but not recommend for a bunch of reasons, including the ones you mentioned.

The first thing that comes to mind in terms of simplicity is replacing the power wire on the water heater with a cord made for a dryer and plug it in to the generator. When your power crisis is over, you can either wire the hot water heater back, or install an outlet.

The next best thing to do i to buy a transfer switch sub-panel, install it, and move the circuits you want to keep using to that sub-panel.

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You know what, I'm going to repeat the answer found here to the same question. Here's that answer, short and sweet and to the point:

ABSOLUTELY NOT!! This is NEVER an option.

You MUST use some form of transfer switch or
interlock, along with the proper male inlet.
Also, a male-to-male cord is called a
"suicide cord" for a reason.

A transfer switch/interlock wired into your service panel is the ONLY LEGAL WAY to do this, and the only safe way.

Look, transfer switches.

Just a few expanded reasons not to do this include:

  • Check out this story, where backfeeding a generator like this started a fire that burned the generator, the neighbor's house, the neighbor's motorhome, the neighbor's race car hauler, a boat, and an SUV. Fun times, huh?

  • Check out this post, where a retired lineman talks about how many times he's seen broken main breakers that still let current through even when they were OFF. Yikes.

  • Backfeeding your generator into your dryer outlet is ILLEGAL, possibly criminally so, or at least totally open to civil prosecution. Tell me that an injury caused by you turning on your generator and feeding power back onto a damaged electrical grid where people are working to repair the lines, and into your neighbor's homes during a crisis won't be actionable? The NEC requires a transfer switch (and not for trivial or capricious reasons). That's good enough for me.

  • the "suicide cord":

    • Seriously, do you actually WANT a #10 extension cord energized with 240V/30A strung across your floor with energized metal prongs sticking out the end of it? What if it accidentally gets kicked out of the wall socket or something? A million things could go wrong. HORRIBLE idea.
  • You'll dump power (stepped up to at least 7,200 Volts by the transformer outside, so it'll go for miles and miles) on the power grid and electrocute a lineman doing repairs.

    • You, or more likely a spouse, visiting relative, or one of your kids, will forget to throw the main breaker before powering on the generator. Or one of your kids' rambunctious friends will fire up your generator when you're not looking, on some sunny July afternoon.

    • Guaranteed, especially since the generator will be needed seldom enough that nobody will remember the entire power-up checklist when the time comes.

    • The whole point of the transfer switch being an interlock is that it only physically permits a connection to one power source at a time.

  • You'll fry your generator and/or anything with electronics in your home:

    • When you've inevitably forgotten to throw the main breaker before powering up the generator, and you've been lucky enough not to have electrocuted a lineman, when the main power comes back on there's a good possibility it will backfeed into your equipment and cook it in one way or another (the timing of the 60Hz wave will be different, possibly amplifying the power to much higher levels, etc., other interesting possibilities).

If you do this, and none of the bad things happen to you, that's what we call blind dumb luck and you really shouldn't tempt fate like that more than once. :-)

Don't do this. It's illegal and just a terrible idea--"Redneck" in the most uncomplimentary way.

  • 1
    His problem happened back in 2011. Hopefully he's got normal power restored by now, and maybe even got a proper transfer switch installed. Chances of finding a transfer switch in the middle of a regional, long-term blackout are more-or-less zero, so saying "don't" isn't always an option. – paul Nov 29 '14 at 4:47
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    His problem occurred in 2011, but the next person looking for sound advice here might be having their crisis tonight, or tomorrow. I don't really agree that "don't" isn't always an option. You can absolutely run extension cords from the generator to the furnace and fridge, maybe the range, maybe the Internet router or chargers for your smart phones, and that'll get you through, then you know to do it correctly when things clear up so that your life can be convenient during the next crisis or simple outage. – Craig Nov 29 '14 at 5:33
  • Honestly, it has got to be easier to pull together a few regular extension cords than to get a #10 suicide cord put together with the correct 240V male ends to backfeed through your dryer outlet. – Craig Nov 29 '14 at 5:35
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    @paul - Daying "Don't" is always an option. If he'd asked if he could temporarily light a fire in the middle of his basement to heat the house, the only answer would be "don't do that because the smoke and carbon monoxide will kill him and his family". When something is so dangerous that it's outright illegal in many localities, besides being a clear code violation, the right answer is "don't do it". The worst time to try out some risky procedure is during a disaster since rescue services may be delayed. If you want to power your house from a generator, do it the right way. – Johnny Nov 29 '14 at 20:06
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You've got the big one covered, turning off the main breaker. Without that, the voltage from the generator goes back out the power lines, into the transformer, where instead of getting stepped down to your house voltage will get stepped up to the line voltage, plus make previously dead wires, live.

Given the options, using a dryer style plug for 220v is the way I would do it in your situation. Back feeding 110v power will only send current down half of the breakers, and it would be easy to swap the neutral and the hot in this situation (with 220v you have two hots, and ground and neutral are effectively the same wire). That said, the proper way is with a transfer switch that would prevent power from back feeding into the power mains and also a plug that doesn't allow for live exposed prongs. These can be installed, but the time to do so isn't when you've been out of power for days. Just realize that using the dryer plug is almost certainly out of code compliance in your state.

Words of caution include checking the amperage of your wiring (the breaker on the dryer will have the number going to the plug) and then avoid overloading the generator. I wouldn't open up more breakers to major appliances than you have amperage to cover (e.g. if the breaker to the hot water say 20 and the dryer breaker says the same, then run that device by itself unless you have a good understanding of how many amps it actually pulls). You can use the breakers to power one device at a time, fridge for a few hours, then the hot water, etc. And when the water is hot and fridge is cold, shutoff the generator to save gas and leave the fridge closed to keep it cool.

Only other piece of advice I can think of is to make sure the exhaust is properly vented. Far too many people don't think and run these indoors, giving themselves carbon monoxide poisoning.

  • 4
    Don't forget that refrigerators can pull a lot of power when they're starting, IIRC something like 2 kW instantaneous. – Niall C. May 5 '11 at 20:06
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    Transfer switch is the way to go. – Tester101 May 5 '11 at 21:00
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    @Tester101: Absolutely, but when you're dealing with a natural disaster, getting a transfer switch installed may take longer than desired. – BMitch May 5 '11 at 21:53
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    @B Mitch: true enough. In that case I would say do what you have to to get through, then have a transfer switch installed so you are ready the next time. But watch out for the angry mobs and looters when you are the only house on the block with power, make sure you lock down that generator so it doesn't walk away. – Tester101 May 6 '11 at 12:09
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    I actually decided against backfeeding since it's a borrowed generator, and we have friends with power 10 minutes away who have graciously allowed us to shower at their house. Good answer though, and thanks! – Doresoom May 6 '11 at 13:41
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A transfer switch is the only way to go, it's only a few hundred bucks, the fee for an attorney for one hour. If you kill someone while back feeding your generator, the cost of a transfer switch is a drop in a bucket.

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    I can't believe your answer has gotten zero votes. Using a transfer switch/interlock is the only LEGAL way to do this. – Craig Nov 28 '14 at 20:48
  • A few hundred bucks? Where? I will buy it right away. Most transfer switches are in the $300+ range, something ridiculous considering that it is a metal box with some breakers inside. Now, I studied Electrical Engineering and I can build one myself for cheap. Wait! I'm not a licensed electrician and can't put one that doesn't have the UL certification. So, I am forced to spend $300+ in a stupid device, half the price of a generator!!! So, my question is, is it illegal to put a transfer switch MADE BY MYSELF? If not, shhhh... I'll do the cheap trick. – Jose Cifuentes Sep 18 '17 at 14:57
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On your water heater that uses 220V and has two elements, you will find that only one element is ever on at a time. When the top thermostat is satisfied, it will send power down to the lower thermostat. If you ever have a problem with the top thermostat or element you will have no hot water. If the lower thermostat or element has a problem you will find you don't have as much hot water as you should. So you are not saving power draw by disconnecting an element.

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    Good to know, but my main question was backfeeding a generator, which I ultimately decided against. – Doresoom Mar 9 '13 at 18:20
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Old question, but common problem.

There IS a sensible, safe, legal middle ground between backfeeding and a full-blown (and expensive) transfer switch: a circuit-breaker panel interlock switch.

An interlock is basically a special set of two pairs of linked circuit breakers that install into your existing circuit breaker panel:

  • Pair #1 connects or disconnects your panel to the power lines outside.

  • Pair #2 connects or disconnects your panel to generator power.

The breaker pairs are designed to physically prevent you from connecting the panel to the generator unless you've already flipped the other pair of breakers to disconnect it from utility power.

An interlock is a fantastic solution if you have a relatively new panel capable of supporting an interlock (most new ones can, though you might have to buy the actual components to do it online... Home Depot & Lowes sell compatible panels, but AFAIK, don't normally keep the interlock components in stock). If you have an older panel, or a more complicated setup (say, a maxed-out panel with one or more additional subpanels), you might have to consider other options... but for most people, an interlock is a great option.

There is one "gotcha" to keep in mind -- to power everything in your house "normally" from a generator, the generator has to be capable of outputting 240v (as split-leg 120v+120v). More importantly, your generator won't run efficiently unless both legs are reasonably well-balanced & drawing approximately equal amounts of power (ie, if you put two window air conditioners and the refrigerator on one leg, and use the other leg to run some lights and a TV, your generator is going to have to work almost twice as hard as it would if you had the big air conditioner on one leg, the small air conditioner and refrigerator on the other leg, and the remaining stuff somewhat well-distributed between the two). With an imbalanced load, the generator basically has to work hard enough to power the larger of the two legs, and just wastes the extra power not used by the other leg.

I think you could still use an interlock with a 120v generator, but none of your 240v appliances would work, and only half the circuits in the house (those connected to one leg) would be powered. You might have to shuffle around a few circuits from one leg to the other in order to make sure that all the outlets you care about would be powered up.

WARNING: before moving circuits from one leg to the other, MAKE SURE the circuit doesn't share a neutral wire with ANOTHER circuit (and that each circuit is connected to a different leg). This is COMMONPLACE, and was considered to be TOTALLY ACCEPTABLE until AFCIs forced a rule change (AFCIs need dedicated neutral wires to work). When two circuits connected to opposite legs share a neutral, their return loads partially cancel each other out, so the neutral wire ends up carrying LESS current. When two circuits connected to the SAME leg share a neutral, their return loads COMBINE (potentially exceeding the wire's rated limits).

The key thing to remember is that generators are NOT "plug and play", especially when temporarily integrated into your home's electrical system. You HAVE to be at least somewhat aware of your home's electrical topography and the amount of power being drawn at any given time from each leg.

  • A big whole-house diesel or natural gas generator (like those sold by Generac) and automatic transfer switch lets you (mostly) get away with ignoring those technical details by virtue of its sheer brute size, especially if you're wealthy enough to not care about fuel costs.

  • With a medium-sized portable generator (4800W-7500W), you HAVE to keep those details in mind, or it won't run efficiently.

  • With a small generator (2500W-4800W), you have to keep those details in mind, or you'll have constant problems with the generator stalling, overheating, and wearing out prematurely (or outright breaking down).

  • With a really small generator (<2500 watts), you have to be intimately aware of those details, and actively manage your power usage at all times. Personally, with a REALLY small generator, I'd stick to extension cords, if only to constantly remind you that you're dealing with a limited resource that can't be taken for granted and requires constant attention.

  • Interlocks can work, and are a much cheaper option. However, when it comes to safety and ease of use, a properly installed transfer switch is hard to beat. – Tester101 Sep 26 '17 at 17:36
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The transfer switch disconnects the neutral as well as both hots. This is why it is so vital. If you know how to disconnect both hots, the neutral AND even the ground from the power company, you can safely rewire your house to a generator. Since this will take a real electrician at LEAST AN HOUR TO UNHOOK (AND LONGER TO RECONNECT) save it for the apocalypse. IF YOU HAD TO ASK THIS QUESTION....GET THE LOCKOUT SWITCH !

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    It happened 4 years ago. No need to panic. – paul Jan 11 '15 at 23:48

protected by Steven Jan 12 '15 at 2:21

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