In my first two posts on “Keeping the lights on” I talked about sizing and selecting a generator. Now that you (and I) have a running generator, let’s talk for a moment about how to use it for powering your home. For the purposes of this discussion, we need to keep a couple things in mind (yes this is my disclaimer).
– First of all, you’re dealing with electricity here. If you don’t feel comfortable working with electricity, DON’T! If you’re uncomfortable working on this type of project you’re probably better deferring to someone who is a trained electrician and has the tools, knowledge and experience necessary to do this type of project safely.
– Secondly, even if you are comfortable working with electricity, BE CAREFUL. Every year more people are killed and injured by 120 volt power than any other type of electricity. I attribute this to both a lack of working knowledge, and to carelessness.
– Third, please, Please PLEASE, DO NOT run you generator in the house. Evey year I hear a stories about someone doing this or leaving it running in their garage with the door closed resulting in them and their family dying from carbon monoxide poisoning. Doing this is tantamount to sitting in your car in the garage with the engine running, windows down, and the garage door closed. It can kill you, and you will never see it coming. You will go to sleep and never awaken. Keep your generator outside, or in an outbuilding and ensure that you have plenty of ventilation.
– And finally, I am not a certified electrician, and while I will share with you how I have my system set up, I am neither advising or encouraging you to do likewise. Be careful people. The last thing you need is to turn an “emergency” situation into a tragedy by carelessness or neglect.
Alright now that the legal disclaimers are taken care of, let’s get the power back on. There are several different approaches to providing power to your home in the case of an emergency. These range from the very simple and automatic (ATS and a fully automated home backup generator system) to the crude but effective, albeit less convenient, approach of simply running a cord from the generator into your house.
Obviously the most simple approach to take is to power up the generator, plug in an extension cord or two and then stretch the cord into the house, plug in whatever, and go. The problem with this is that your overhead lights, well pump if you are on a well, hot water tank, etc won’t work. The solution to this inconvenience it so use a method called “back feeding”. What this entails is essentially disconnecting your home from street power and then replacing that with power from your generator. This sounds like a complicated solution, but chances are pretty good that you already have most of the necessary pieces of equipment in place.
To back feed your home with emergency power you need to have a basic understanding of how your home’s electrical system works. Power comes into your home from the street either overhead or underground, then passes through the electric company’s meter. After leaving the meter, the power comes into your home’s electrical system. Most homes these days have a circuit breaker box (not a fuse box) so that is the design we will discuss.
Image via Wikipedia
After passing through the meter the electrical power for your home enters your breaker box and goes to your Main Breaker or Service Disconnect. This is typically a large breaker at the very top or bottom of your panel and it always has the largest amperage rating of any of the circuit breakers in your panel. This Main Breaker or Service Disconnect serves as the master overload protection for your home, as well as your main means of disconnecting your home from street power. Turning off “the Main”, will shut down (disconnect from street power) the whole house. Under typical operation, the power leaves the main breaker and flows through the panel through a system of metallic conductors called bus bars, then into your individual circuit breakers and out into your branch circuit wiring to the lights and devices in your home. Incoming power into your home is made up of 2 separate 120 volt feeds (often referred to as “legs”), a “Neutral” conductor that serves as a return path for voltage from a device and a “Ground” conductor for added safety against shock. The 2 separate legs of power alternate their positions in your breaker box so that every other breaker on either side of the box is on a different leg. Panels are typically labeled with numbers, odd numbers on the left, even numbers on the right. This being the case, as you look at the breakers in the breaker box, circuits 1 and 3 are on different “legs” but 1 and 5 would be on the same leg. Also, the breakers directly across from each other (1 and 2 for instance) are typically on the same power “leg”. Understanding this design is important so you know how your system is working when you connect your system to emergency power especially if your generator is a 120 volt output only and does not supply a 240 volt output with two “legs” or circuits of power. Even if your generator only produces one hot “leg (120V) you can power the essentials by having the breakers for your essential appliances moved to the same “leg” of power in the panel. This can be done by moving the breakers around in the box if necessary. To back feed your home’s system, you simply turn off the main breaker (Service Disconnect), connect your generator to one of your home’s electrical outlets and let the power flow through your existing wiring. Simple enough right?!
Let’s take a closer look. The first thing to decide is where you will be connecting your generator to your home’s electrical wiring. Depending on the output of your generator (in terms of voltage and amperage) you may be limited to the number of places where you can make this connection safely. An electric dryer outlet, an electric range (stove) connection, or a connection for a Welder or other large 240V appliance is a great place to back feed your system. In my case my generator has a 30 amp, 240 volt receptacle on the side of the generator, so I need to match that to a minimum of another 30A 240V receptacle in my house. Now understand that the actual plugs themselves are not likely to match physically, but as long as the voltage and amperage ratings match you are in good shape. The exception to this rule is that if you would happen not to have a 30 amp outlet in your HOME but you had a 40 or 50 amp outlet that would be an acceptable alternative. You can safely feed your generator’s 30 amps of power into a 40 or 50 amp circuit in your home, but do not go the other direction. DO NOT attempt to feed your generator into a circuit with a LOWER voltage or amperage rating than the rated output of the generator. In my case, here are a couple pictures of the receptacles on my generator and my home (actually my shop) wiring. In my case I decided to feed the power back to my house from the welder receptacle in my shop. This would allow me to store the generator in the shop and use it there without having to move the genset to the house. This would also allow me to run the genset in the shop in case of inclement weather without running the risk of carbon monoxide poisoning.
Generator Receptacle (this is of the “twist lock” variety):
Welder receptacle in my shop:
Now that we have the design portion of the solution out of the way, let’s get the tools out and get our hands dirty. After determining the type of cord ends required for the installation, the next step in back feeding you wiring is to make the cord. In most cases, you will need 2 male cord ends, one for the receptacle on your generator and one for the receptacle in your home wiring system. In my case one end needed to be a 30A 120/250V 4 prong twist lock male cord end, and the other needed to be a 3 prong 30A 12/240V angled prong male cord end. I debated for a while about what to use for the cord, but I discovered a used heavy duty extension cord that I had forgotten I had. It was slated for disposal on a job site I was on due to having a nick in the insulation and a couple of bad cord ends. It was, to my surprise a 10ga 3 conductor cord, which was heavy enough to carry the load I was applying. A note here about wire gauge is to be sure that you are using a large enough cord to carry the loads you are intending to support. Click Here for a link to a handy calculator to aid in the selection of the proper size cord. The cord should be sized for the full output capacity of your generator. Be sure to account for the length of the cord, since it can drastically impact the size of the wire required. For my application, the calculator says that I am fine to use my #10 wire for a 30 amp load at 240 volts over a distance of 75 feet. You may wonder what I did for the 4th prong of the plug on the generator. This was intended to be the ground plug, but since my outlet in the wall did not have a ground, it would not have done anything anyway. Ideally, if I were to install a dedicated receptacle for the use of this generator, which I may do at some point, it would have all 4 conductors (2 hot legs, 1 neutral and the ground). The reality of it is that the generator is not “generating” a ground anyway, so in my mind, grounding the generator to the earth using a ground wire and rod, or similar system is a sufficient safety measure to prevent electrical shock.
The finished cord ended up looking something like this:
Now that the cord has been constructed it is time to try it out. This is where it important to ensure that you understand the electrical design we went over above. Failure to understand the design and take the proper approach in testing and using this system can be a dangerous proposition. Let me outline the steps that I used to test my system.
1- Because I didn’t want to fumble around in the dark any more than necessary, I started the generator with the shop lights on with street power.
2- Turn off the street power (in this case the power being fed to the shop from the house) by turning off the Main Breaker (Service Disconnect) in the breaker box.
3- Turn off the branch circuit for the plug that you are connecting to
4-Plug the cord into the receptacle in the wall (in my case the welder receptacle)
5-Plug the cord into the receptacle in the generator (note I didn’t do this first because if I did the exposed prongs on the other end of the cord could be “hot” with live electricity).
6- Switch on the 240V output of the generator.
7- Switch on the breaker for the receptacle you’re plugged into (again, in my case the welder circuit).
8- Bask in the glow of your off grid lighting and enjoy the satisfaction of knowing that you can generate your own electricity.
At this point you may notice that your lights are not as bright or even, especially if you are using fluorescent lighting like I am. This is mostly due to the fact that your inexpensive power generation system does not produce as “clean” a power as the multi-billion dollar system that the power company has designed and installed. This is to be expected and is nothing that you have done wrong.
Now while enjoying the comfort of your home brewed electrical energy, you may wonder, “How will I know if the street power comes back on?”, and this is a legitimate question. One way would be to watch for the lights to once again come on at the neighbors houses, or for the street lights to come back on. But if you live in a rural area like I do, and or your neighbors have their own generators, this won’t work. One way would be to have a qualified electrician install a small light onto the incoming power BEFORE your service disconnect. This is a little iffy by the electrical code since the circuit is unprotected, but you could install an inline fuse if you’re really concerned about it. Explain to the nice electrician what you’re trying to accomplish and they are likely to understand and help you to do this safely. One thing is for sure though, you don’t want your Main Breaker (Service Disconnect) turned on and your generator running when the power comes back on. The sparks will fly and you will let the smoke out of your generator. Putting the smoke back in the generator is an expensive proposition.
Once the commercial power comes back on, to transition back to street power you would use the following methods (essentially the reverse order of the process above):
1- Switch off the circuit breaker for the receptacle the generator is plugged into.
2- Switch off the generator’s electrical output (it’s not a bad idea to allow the generator to continue to run to cool itself down during the remainder of this process).
3- Unplug the the electrical cord from the generator’s receptacle.
4- Unplug the cord from the receptacle in the wall.
5- Turn the circuit breaker for the receptacle in the wall back on.
6- Turn on the Main Breaker or Service Disconnect in your panel.
7- Shut down the generator now that it has had a few moments to sufficiently cool itself.
This has been a bit of a lengthy post, but hopefully you can see from this that it is doable to use your home’s electrical system to distribute the power from your home generator in the event of an emergency.
Again, I am all about the DIY mentality, but if you are uncomfortable tackling an electrical project of this scale, it is best to consult the advice and expertise of a professional. When safety is on the line, it pays to have some qualified help.
Happy Generating ’til next time.