A generator is a core component to many people's emergency preparedness plans. (Maybe you have a cool charcoal powered or a multi-fuel generator.) However many fail to think through how exactly they will power the items they want to run when the grid is down.

In June of 2012 my family experienced a 10 day power outage. It was eye opening. It was 100 degrees during the day with periods of heavy rain. I had to run a sump pump to keep my basement dry, a refrigerator, freezer for food preservation, a portable AC unit in the living room to protect my infant, we charged phones, and ran the wifi router. I had power cords everywhere. It was a pain. I decided then and there I would find a better way.

A generator transfer switch is the legal and proper way to power your home with an emergency generator. There are three main types: automatic, manual transfer sub panel and a breaker interlock. Each has varying degrees of complexity, benefits and expense.

Automatic transfer switches will sense a power loss, start your standby generator and automatically move your load to the generator. These are awesome - but very expensive and require a full time dedicated standby generator.

Manual transfer sub panel switches are good option. They are less expensive than the automatic transfer switches (Starting around $300) and can be used with a portable generator. They typically only cover a few breakers which was problematic for me.

Breaker Interlock is the option I chose. It is National Electric Code compliant and is in my opinion the least expensive and most flexible option. My setup cost was just under $150. In this setup you use a breaker to energize your existing breaker box. Switching it on is easy and safe. My wife did an unassisted dry run in under 5 min - which included getting the generator out of the building.

The breaker interlock system has come in very handy for us. We can turn on overhead lights, wash clothes and keep our food cold, charge our phones, run the internet and much more....all while keeping our doors and windows closed and no tripping on extension cords!

I am not an electrician. After much consulting and over sight from a licensed 25 year Master Electrician I believe these instructions to be correct and accurate for my jurisdiction. Electrical codes vary from place to place. In my place of residence home owners are allowed to do their own electrical work if it is up to code. You are responsible for any code violations, permits or awesome good stuff that comes from doing a project like this.


I've listened to and have even seen people using a double male plug to energize their house during a power outage. This is dangerous.

  • It is an electrical code violation.
  • It is illegal in most places.
  • It is a fire hazard. The power created by your generator is generally greater than the rating for the receptacle, wire and breaker.
  • If you don't disconnect your main breaker it can shock the power company linemen - and you will get sued.
  • You can easily get shocked because the male plug prongs are exposed.

Step 2: Determine Your Generator Plug Type and Amperage

First you have to figure out what type of amperage and plug type we are working with. You only want to do this on a generator with a big round plug. This will provide 220V (in the US) and power both sides of your breaker box. You will see the amperage written near the plug. Mine is a 30 Amp L-14-30.

For your convenience these are the most common sizes:

Nema L14-20 - 20 amp
Nema L14-30 - 30 amp
Nema CS6365 - 50 amp

Step 3: Supplies

Gather your supplies.

For the sake of this build we are going to assume you have a 30 amp plug on your generator - like the one shown. If your have one different please adjust your supplies.

Breaker interlock kit. Buy a UL rated device that fits your specific breaker box. These have been tested and validated to work. Many insurance companies and jurisdictions require the UL rating.

30 Amp 2 pole (double) breaker. Again you will need to buy one that fits your breaker box. All breakers are not the same.

Wire. I bought 10 feet of 10 gauge wire in black, red, green and white.

30 Amp power Inlet box.

Schedule 40 electrical conduit and fittings

Conduit body

Conduit glue

Flexible Non-Metallic Conduit and fittings (optional)

30 Amp generator extension cord. (Search Amazon for (your plug type) extension cord.)

Notice how all the amperage match. If you are using a 50 output on your generator you will need a 50 amp breaker, 50 amp power inlet box, a 50 amp extension cable and 8 gauge wire.

Step 4: Drill (or Find) Access Hole

Measure 5 times drill once.

My house had an conduit old hole in the foundation. Most people will need to drill one. A hammer drill is extremely helpful for making one. Try to get the conduit hole as close to the panel as you can.

Step 5: Mount Power Inlet Box

Remove the front cover from the power inlet box.

Remove a knock out and attach the PVC fitting. You can see here I opted for the water tight connector. Glue works just find too.

Using tapcons mount the power inlet box to the wall.

Step 6: Test Fit and Glue Conduit

Use a hack saw and cut the conduit to length.

Don't glue it until you know it fits. Once you are good glue it down.

Step 7: Wire the Generator Inlet Plug

Once the glue is dry we can start to work on the wiring.

Remove the cover on the conduit body. Pull the wires through one at a time attaching them to the plug as you go along. Remove about 3/4 of an inch of the insulation. Use a large flat screwdriver or a nut driver to tighten the terminals.

Green - Ground to the power inlet box.
White - Common, W terminal
Black and Red - Load - either X or Y terminal.

Step 8: Push Wiring Inside

Push the wires through the conduit into the house one at a time.

Replace the conduit body cover, checking proper fit of the gasket.

Fill any gaps between your conduit and the house with silicone or expanding foam.

Step 9: Prep Breaker Box for Wires

Turn off all the branch breakers and the main power breaker.

Remove the front panel of the breaker box by taking out the four screws.

Remove one knockout and screw in conduit adapter or in my case a blue non metallic conduit adapter.

Pull wires through conduit and into the box.

Step 10: Create Open Breaker Space

The breaker interlock method requires the to most upper and right breaker space to be free.

Generally you will need to move a breaker or two down. Most boxes will have enough spare wire to move things around a bit. If you do not have enough room and your breaker is 30 amps or less you can use a short piece of insulated wire and a wire nut.

DO NOT wire nut copper and aluminum wire together. They will corrode over time. You will need to pick up a wire splice at your local home store.

Step 11: Install Generator Breaker and Wires

Install your new breaker in the freed up space in the upper right of your breaker box.

The red wire goes to one terminal on the breaker and the black goes to the other.

The white wire goes to the common bond rail in the box.

The green wire goes to the ground rail.

Note: In a 2 wire home like mine - meaning no 3rd ground wire in the outlet box or the outlets in the home. It is acceptable in my jurisdiction to put the green ground wire to an open common terminal. It is not appropriate to use the ground wire for the common at the outlet.

Step 12: Install Breaker Retainer

Now it is time to lock down that breaker from moving. Install the retaining bracket. My retaining bolt was located between the main breakers and the 30 amp breaker.

Step 13: Install Inter Lock on Panel Cover

Flip the cover over and use the provided template.

Pre-drill the holes and then finish them out withe the bit size noted in your instructions.

Turn the panel back over and install the sliding interlock bolts.

Reinstall the panel with all the breakers in the off position. With the main in the off position turn the generator breaker to the on position. Ensure the interlock allows for the on position. You may have to shift the position of the panel cover.

Turn the generator breaker to the off position and drop the slide so it can not be turned on. Ensure the Main can be turned to the on position. Adjust panel cover if it will not.

If it does turn the breakers on one a at a time - with a 5 second delay between breakers. This will distribute the start up load.

Attach decals included in your kit to your breaker box and the outside service box.

Step 14: Operation

Time to load test! Write down these instructions and put them in your breaker box.

  1. Confirm power outage
  2. Place generator 15 feet from your home - with the exhaust pointing away from open windows and doors
  3. Start generator and ensure normal operating speed
  4. Attach generator extension cord to the generator with an inward push and gentle clockwise turn
  5. Attach extension cord to the home power inlet box with an inward push and a gentle clockwise turn
  6. At the breaker box turn off all the breakers
  7. Turn the main breaker off
  8. slide interlock up exposing the on position of the generator breaker - turn generator breaker on
  9. Turn on selected breakers with a 5 second delay in between each - ensuring the generator takes the load.

Avoid turning on HVAC, standard hot water heater and the stove unless your generator can handle it. As long as you can get past the initial start up load you can run a lot off of 30 amps.

Power off sequence:

  1. Turn off all branch breakers
  2. Turn off generator breaker
  3. Slide down generator interlock exposing the on position of the main breaker - turn main breaker on
  4. Turn on branch breakers one at a time with a 5 second delay between each one until they are all back on
  5. Power off generator and allow to cool
  6. Remove generator extension cord.

Enjoy your set up. It has come in very handy for us. We can turn on overhead lights, wash clothes and keep our foo

<p>To More Cowbell, (love the name btw) As a veteran Master Electrician I just want to say &quot;Well done&quot;. I just hope folks won't get lazy and put off the MOST important step in your article and that is the install of the &quot;INTERLOCK&quot;. So easy to put that off because it will work without it but THAT is the killer if not done.</p>
<p>My main breaker is not in the breaker panel but is mounted on the opposite side of the house. How would you recommend I compensate for this?</p>
<p>you could mount a heavy duty 3 phase on off on toggle switch between the fuses of the main and the generator to the house fusebox you can do that near the housebox</p><p>http://www.bundupower.co.za/mcs.php</p><p>you can use it as the mainswitch between main and generator basicly it will switch between one , then off , then the other , never together / combined </p>
<p>The only problem with this is that the toggle switch would have to be listed and labeled for the application. I'm not sure you'll be able to find one.</p>
<p>the one i showed actually WAS for exactly that setup and was labeled gen and main </p>
<p>You can put a sub panel next to your breaker panel. In between the two, you can wire a transfer switch. Wire from a 2 pole breaker (sized according to your generator) to the transfer switch (like this one: <a> http://www.homedepot.com/p/Reliance-Controls-60-A...</a> Wire the generator to the other line input. Wire the sub panel to the load output side. Then<strong> move </strong>only the circuits that you want to be backed up by the generator from your original panel, to the new sub panel.</p><p>Follow all local codes and the NEC for securing, bonding, etc. and you should have no problems.</p>
<p>Thanks Jim!</p>
<p>Breaker interlock is the same system we run and it's great! We did a test run of refrigerator, sump pumps and a/c going all at the same time and our generator barely hiccuped. </p>
<p>Does the power inlet box have male terminals?</p>
<p>Yes - but they are not energized until the generator plug is attached.</p>
<p>Ahh, ok. I was wondering about that too! :-)</p><p>Great instructable. </p>
<p>I generally shudder when I hear or see people try to set up a generator for all the reasons you point out. You did an excellent job and I like how you insure your generator is never tied into the grid. @ radiat1 I have used a similar system for about 5 years now my hots go through a transfer switch and my commons (white) are solid to the sub panel since the common and ground are tied together at your main panel if you were to send power to the common it would trip you generator breaker. I have had no problems and my number one concern is not killing a lineman. </p>
<p>Great Job pointing out the suicide plug. Male to Male extension cords will kill you and burn down your house</p>
<p>I put my own generator power system in my home, it is separate from my homes regular power system. I plug my generator into the system from out side with one heavy cord that is male on one end and female on the other. It feeds power to just a few outlets in the house to run important things but not my whole house. I have never had any problems with anything heating up or tripping the generators breakers. You say that if someone uses that double ended cord, which is stupid, that it is also a fire hazard because the generator puts out too much power for that outlet that you plugged the cord into to handle. I don't know what kind of a generator you use but every generator I have ever had anything to do with including my own that I use now has one or two 110 v outlets on it with a breaker. How is that breaker going to let the generator put too much power out and burn your house down? And if it was going to put too much power out why wouldn't it burn the breaker and outlets on the generator out first? I could see where it would be a big problem if the generator didn't have a breaker and you were running the whole house through that one outlet that you plugged the cord into. It would heat both the generator and house outlets up and also the cord</p>
<p>I have a RV plug outside where I plug that into the generator when no power! The other end of that cord ends up in my basement near the furnace with a four outlet box that is grounded! The furnace and an extension cord goes to my downstairs Satellite and TV. Another extension cord goes to my down stairs microwave on the other side of the wall where the outlets are! No connection with the homes electrical system means the circuit breaker at the generator is the protection! If the power failure takes more than a day I will connect my down stairs frig that is next to the microwave! We live in Lake Tahoe Basin and have several power failures and with the rest of the home electrical separate, I like this better that when the power comes on. the lights come on! It takes 15 minutes to put everything back to normal! </p>
<p>I just have the generator RV outlet set on 115 volt because I don't plan on ever hooking up a 220 volt system. The other outlet not used I have used to charge my 4 D heavy duty battery if it was used that powers my 3,500 watt inverter that runs the furnace, and frig at night separate from the generator with it off during the night! I have also had the Sat/TV connected for a few hours before we went to bed and when I woke up in the morning! Of course I also have a nice wood fire in the stove downstairs as well! </p>
<p>I only would recommend using a sub panel method with the interlock breakers in the sub panel with necessary circuits brought over to your sub panel. It's a lot more work but still cheap and safer. Also, don't start the generator until you plug in your cord to the generator and inlet box. It is not safe to start generator then start plugging everything in as recommended in this tutorial.</p>
<p>Question. If the interlock plate is required and a very important step in this project, why is this small piece of metal plate so expensive? At around $69, this will discourage you average diy'er from following this step..... Logic would dictate this would be very affordable so as to not discourage folks from skipping this important safety step!</p>
<p>My generator on has two 120v outlet.</p><p>Can both of the outlet use some kind of Y harness to combine them together to give 240v 2 poles with a round plug at the end?</p><p>Use the female plug end to plug in to a outlet box that is wired up to a sub breaker panel with a interlock breaker?</p>
<p>?,I ve never seen the Generator breaker Interlock kit even on the shelves here in Alberta Canada.I guess they are not allowed to be installed here.But I can't see why not.They seem to be safe for standby setup.And if someone knew where to get on let me know if we are allowed to install this here. </p>
<p>What can be done if your main box doesn't have a central main breaker?</p>
<p>Just one thing in England you would and should not get away with the this sort of wiring Just to dangerous sorry.Again a Vet Master Tec Electrician</p>
<p>Roger. </p><p>The typical know it all that tries to belittle others trying to make himself look smart. </p><p>You clearly didn't read the article as you're complaining about a image that he specifically used as an example of something BAD to do..</p>
<p>Roger I curious. Why would this not be expectable to do in England? </p>
We Electricians In England have a Book called the electricians Bible It is brought out by the Institute Of electrical Engineering. This book gives rules For domestic wiring to industrial wiring on how to install circuits safely. You ask why just look at the first photo into the project,it shows a cable with two plug ends, exposed conductors at both ends. say you had these connected in a garden situation, one in a generator the other in a socket to the house out side wall. two children running plying near the wall socket,one trips and pulls the plug of of the socket the other fulls on the opened ended brass contact. Bang One dead child. I would not like to see that would you. I do not think so. In any wiring to do with house holds must come up to IEE regulations. Safety come first in my book<br>The big question is what protection is in place if the mains power is switch back on
<p>Hi Roger. </p><p>I'm just curious how the *code book* is going to prevent this?? Almost all countries have some sort of electrical code. The NEC here in the US, is pretty robust, as well. However, some people are going to do stupid things! These people live in the UK as much as they live in the US.</p><p>In some states in the US, people are aloud to work on their own electrical, however, an inspection by a qualified, municipality appointed inspector is required. The inspector ensures the work meets code requirements. </p><p>I'm sure this is not new to you, and I don't know the UK's position on this. But, if anyone does the work on their own and doesn't have this work inspected, well, there you have it... Dead child...</p><p>Back to my question, how does the UK seem to overcome this issue?</p><p>I truly am curious..</p><p>Thanks,</p><p>Chip</p>
I recommend that you read through the instructible and not just look at the pictures.
<p>Roger, he showed the double-male &quot;suicide cord&quot; as an example of what *NOT* to do.</p><p>Otherwise, the rest of the hookup with the interlock plate is foolproof and NEC-approved.</p><p>When the mains come back, that breaker is open, and can only be closed after the genny breaker is opened.</p><p>You may be a wire twister Par Excellence, but I don't think much of your reading comprehension.</p>
<p>You must remember if you are as good as you say you are jack of most trades that there are people that will try any thing that is cheap and will do the trick they do not know you have to be NEC registered, to work on other people houses but one thing I have learnt over the year you do not show what could be, as some one will do the quick and easy way of doing it. I am aware of the way to install this type of equipment. using the Book of Regulations that apply to England. I have found in England not every body knows about t he IEE regulations , But I tried to explain the reasons In a simplified way using children. which people pay attention to. To under stand one thing, what looks good in America is not always allowed in England. So I say this to anyone always check the regulations of the country you are going to use the equipment in. But if you must make a comment Please read Gregfranks of three months ago. If you do not Know you should not be touching it .Safety First</p>
<p>Roger please READ what is written in step one and then remove your comments! </p>
<p>Roger, your comments tend to indicate that you did not actually read the article...?</p>
<p>Hello,</p><p>Thank you for posting this instructable. I have been looking for DIY instructions on how to add a backup generator to a house and thankfully found your instructions. I have a quick question. In the home I currently live in the previous owner had a water pump installed in the back yard. She had the pump added on it's own circuit breaker (120 volts). Could I use that same wiring to add my back up generator? The pump is 120 volts. Cheers!!</p>
<p>NIce Job. Only thing else for the install could be installing to the power </p><p>inlet box right over the hole going into the basement. Just a thought</p>
<p>Yes...but it would have been behind my gas grill so I moved mine down a bit.</p>
<p>I may have missed it in a previous question/comment, but will this power both sides of the circuit panel assuming it is being fed with 220v? Thanks!</p>
<p>Yes - absolutely. You need to make sure the breaker you use to feed from the generator to the panel is a double breaker (used for 220V applications).</p>
<p>I would suggest that before anyone do this &quot;DYI&quot; they check with their local code enforcement. Some areas do not permit this type of DYI work. I for one get irrritated with it because I know I'm better QUALIFIED, than many CERTIFIED people doing the work.</p>
Thank you for your inquiry and for thinking this man has some think to say. I first must make it very clear that the project I spoke about has many good things going for it. But let me ask you a question. Have you ever been to a caravan site were some one has a small generator hooked up to the caravan? Have you really looked around that sited caravan. Not many people do. There it stands up on three rubber tires and the generator a few feet away sitting on the ground making electricity(240 Volt) in the UK. But is it truly safe. I think not. But if a bit of understanding by the owner of said caravan it could be, there is no proper earthing arrangements made, a 1mt earthing copper rod driven into the ground and connected to the metal chassi and then to the electrical earthing of the circuits in the caravan. Would be in order. But not every body has that electrical knowledge.<br>To go into this situation about rules and regulations and the different country's would take forever and a day but I will keep it short as possible. I can not speak for the US. I have traveled a lot in the US, and being a electrician I view what I see and compare to the UK installations, As I mentioned before we have very strict rules, which split up to cover different area's of installation:- Industrial, light industrial, Farming, Domestic, and all outside work from high way lighting to gardens sockets and lighting. Lets take a garden shed installation, One 13 amp switched socket and a light with switch. Before any work is undertaken under the current regulations(We shall call them reg's) you must test the main and earthing arrangements at the meter head this is called a Earth Loop Test. And check the sizes of the meter tail and earthing cable is up to standard required sizes by the Reg's. this is before any cable fittings has been installed. you have to bring this part of the installation up to spec, I have not started on the consumer unit (Fuse Box) yet. You have to decide whether the customer wants to pay for a complete test and check on circuits in the existing consumer unit. The law is last man working in this area has to take responsibility for it, so you have to test them out or a new consumer unit (Fuse box) just for that circuit you are going to install. You will only be responsible for that circuit any new circuit into existing fuse box or new.In any way you do the installation a Rcd must be used for out side use. I could go on but it would get very boring. From the fuse board we do a three wire feed system Earth, Phase and Neutral. The main thing is the earthing of out side work. If you run a generator, they that is the ruling electrical body like to see a 1mt earthing copper rod driven into the ground adjacent and connected to the generator and not to assume that the circuit the generator is supplying is already earthed. that earthing circuit has to be tested also. In my book and in what you mentioned the last man working on the circuits can be held responsible in law. So you cover your AH as we say over here. And if you are not a electrician, really the only thing you can do is change sockets and light fitting only, like for like, but not in the kitchen, bathroom or the garden areas you have to call for a electrician in to work in these areas.. Can you say that the Do It Yourself persons would have the test gear to test that generator circuit out to a professional Standard. No. The two countries have very different rules and standard, one is the voltage in our domestic house supply is 230-240volts at 60 cycles AC. Get a belt from that and you will know all about it. I think the US think the UK have the same rules in some ways yes but in others no our rules are a lot tougher than yours. But all I can say is this if you want to check our rules and Reg's look on the Webb for Institute of Electrical Engineering current regulation, I think the 17 edition. I am not out to bash the American ways but to inform the UK numskulls over here to be careful and to be aware that Safety come first and to be safe is to know the rules. <br>
<p>I made a power transfer cord to connect the 220 generator output to the 220 dryer output in the garage and simply dropped the main breaker at the meter so as not to back fry the power company crew. <br></p><p>That allowed the generator to power every outlet in my house. No extension cords. I simply powered what I wanted, when I wanted, keeping in mind the total output ability of my generator. </p>
<p>Excellent write-up! One question: why did you choose to run PVC conduit on the outside when the Reliance inlet plug could have been mounted right on top of the access hole? </p>
Very observant! I only used conduit so the outlet would be in a place that was convenient to reach. This would also be useful if you had a specific location you wanted the generator to sit.
<p>Could you please identify the &quot;plug&quot; in step seven....is it a male or female? I wish you had shown a photo of the &quot;plug&quot; from the other side. I assume it is a male plug to fit the female end of the generator extension cord? What is the name of it, like a model number of the particular one YOU used?</p>Step 7: Wire the generator inlet plug
Great question. <br>It is called a &quot;Power Inlet Box&quot;. It has male terminals. You can find them at any big box home store or online suppliers like Amazon. I used this one from Lowe's.<br><br>http://www.lowes.com/pd/Reliance-30-Amp-Generator-Power-Inlet-Box/3133095<br>
<p>My house has the old fused breaker box. In the event of a power failure there is nothing for me to do but to manually pull the main fused disconnect then pull the fuses at all the various 20 and 30 amp stations in my box before turning on the breaker for the generator outside. Am I correct that circuit breaker for the generator can be installed in a fused box? </p>
<p>My house has the old fused breaker box. In the event of a power failure there is nothing for me to do but to manually pull the main fused disconnect then pull the fuses at all the various 20 and 30 amp stations in my box before turning on the breaker for the generator outside. Am I correct that circuit breaker for the generator can be installed in a fused box? </p>
<p>This is an interesting concept that may not be available in all areas; http://www.generlink.com/about_generlink.cfm</p>
<p>Please excuse the newbee post...from my study of physics some 30 years ago Ohm's law gives the relation between voltage and amps ( V = IR). The laws relating to transformers are Lenz's law and Faraday's law, and the equations </p><p><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/e97705d62656675e5b456224e3d96a00de08b828">.</p><p><em>p</em> is for primary winding and <em>s</em> for secondary</p><p>I think that Palombo50 may have been remembering that transformers will not pass DC voltage or current. Unless there is a change in the voltage there is no flux generated. Voltage is generated is related to the turns ratio of a transformer and the rate of change of the voltage. The best example of this is the automotive ignition coil, very high turns ratio and 12VDC to zero in milliseconds yielding tens of thousands of volts at low current. </p><p>whis is which is about lenses (optical)</p>
<p>Interestingly the old ignition coils were independent of turns ratio and input voltage. The coil core was saturated by the primary current and when the points opened the collapse of the magnetic field and the number of turns in the secondary resulted in the high voltage. The capacitor was to prevent the back emf on the primary side from arcing across the points.</p>
<p>I need help, please. I have done this exactly as stated and when I start up my generator and have main breaker disconnected and all breakers flipped off as soon as I plug in the 120/240V L147-30 into the box the generator breaker pops. What have I done wrong? I do have the interlock kit installed as well. </p>
<p>Is the genny breaker a ground fault interrupter? You could have a ground issue with an older 2-prong plugged appliance.</p>

About This Instructable




Bio: I'm a computer engineer - but please don't judge me by that. I heat with wood, fix broken things and love camping with my ... More »
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