There are several things to consider when you want to be able to use a generator at your house for emergency power backup. We have been getting more calls for this type of work over the past several years due to wildfires, ice storms, power outages, and natural disasters. Below we lay out the points you want to think about before buying a generator or getting wiring installed at your house.


Manual versus automatic

First of all, when you call and tell us that you want to hook up a generator at your house, we need to understand the type of system you are wanting to use at your house. There are two main types: automatic and manual. The automatic style is also sometimes called a standby generator.

Installing an automatic standby generator at your house is an expensive project and the generator requires consistent maintenance throughout the year (oil, fuel, battery, air filter, valve adjustment and testing of the system, etc.). These generators run on either natural gas or propane and can require a large amount of fuel to run. If you do not have natural gas at your house and you want to use propane, you will need to install a very large propane tank at your house, which needs to be buried to keep from freezing, to run the standby generator. This option is not commonly used in our area thus we do not install automatic generators or automatic transfer switches for generators.

Generator blog three elements you need are generator, mechanical interlock, and outdoor power inlet box

What we do install for our customers is the more common in our area mechanical interlock and wiring for their manual generators. Manual generators are the portable generators you see for sale at your local hardware store or big box store that are often used at construction jobsites or for temporary power.

In order to use a manual portable generator at your house with your electrical panel, we will need to install a power inlet box outside and a 30 Amp or a 50 Amp breaker in your panel along with a mechanical interlock (see below section for a discussion about which generator breaker size might be right for you). A mechanical interlock is a device installed in your panel so that you can turn off the main breaker and then turn on the breaker for your generator (examples are shown in the pictures above). The mechanical interlock prevents you from being able to have both breakers turned on at the same time. If you did have them turned on at the same time, then your panel would be receiving power from two sources and there would be an explosion. This is why they need to be separated so they cannot be on at the same time.

DuroMax generator dual fuel model XP1300HX


Selecting your generator size/model/fuel source

It can be overwhelming when shopping for a generator to know which features you will need and want. Here are the main considerations for you to think about.

  • This is mostly a personal preference. Some people prefer to buy specific brands and we don’t advocate for one brand over another. When we are considering a generator, we look more closely at the other features discussed next.
  • Fuel source. You can buy a generator that runs only on gasoline or one that is dual fuel (can run on gasoline, propane, or natural gas). We generally recommend getting a dual fuel generator because most gasoline has a percentage of ethanol in it. When ethanol is stored for short periods of time, it produces water. If you pour gasoline into your generator and it sits for six months, a portion of the fuel will be water and your generator won’t run. Then you will need to drain the gas tank and clean the carburetor to make it run again. You could add fuel stabilizer when you pour the gasoline in originally, but that is just another step in the process that you might forget about or not want to worry about.
  • Generators installed with 30 Amp versus 50 Amp outlets (30 Amps x 240 volts = 7,200 watts and 50 Amps x 240 volts = 12,000 watts). This is the most important feature you need to be looking for when you buy a generator. If you buy a smaller generator that only has a maximum of 30 Amps, then you will possibly not be getting enough power to support your needs during an emergency. This is especially important for people who live just out of town and rely on a well for their water. Well pumps typically run on a 30 amp circuit, so if your generator is only good for 30 Amps and you need to run your well pump, you will not have enough power to use any other circuits in the house. We always recommend our customers spend the extra money to buy a generator that will support 50 Amps so there is less concern about having enough power to run their essential items when the power is out.
  • Peak watts and running watts. You might notice in the picture above that there is a slight difference between the peak watts and running watts when you are using gasoline versus propane. Running watts is the usable power while the generator is running at regular idle. Peak watts is the power that can be generated in short bursts when appliances need a quick power surge when they come on. For instance, some appliances require a burst of power right when they start up to get the motors and components running. Then the furnace switches to a lower steady power usage while it is running. In our opinion, the difference of wattage between gasoline and propane is not great enough to impact your power usage. We still recommend getting a dual fuel generator and using propane/natural gas over gasoline.


How much power will I be using?

Most houses have a 200 Amp electrical panel, but you might also have a 150 Amp or 100 Amp panel running your house. No matter what the size of your electrical panel is, your generator will be limited to 30 Amps or 50 Amps. This means you will need to figure out which circuits you want to use during an emergency and how much power each of those circuits will use. You may end up needing to cycle from one circuit to another so you can use one appliance and then switch to a different one. If you end up using too much power at one time, your generator will simply shut off. Then you will need to turn off some of the circuits and restart the generator so you are not trying to use as much power all at once.

In order to figure out which circuits you will want to use during a power outage, one of the first steps you need to take is to make sure your electrical panel is labeled correctly so you know what each breaker is controlling. You can read our blog here about how to properly label your electrical panel so your circuits can be easily identified.

Calculating Amps from Watts and Volts for microwave, space heater, and water heater

In order to figure out how much power your appliances use, you will need to do a little research and math. In the examples above, we have chosen a few items that you might want to use when the power is out: a microwave, a space heater, and a water heater. Your appliances list their power usage in watts, but your electrical panel lists everything in Amps. This is where you will need to do some math.

In our example above, the microwave is 1,000 watts and runs on 120 volts, so you will need to divide 1,000 by 120 to get the Amps used. That come out to 8.33 Amps.   The space heater is 1,500 watts and runs on 120 volts, so you will need to divide 1,500 by 120. That comes out to 12.5 Amps. The water heater is 4,500 watts and runs on 240 volts, so you will need to divide 4,500 by 240. That comes out to 18.75 Amps. So, if you total all three together, then you will be using 39.58 Amps if all three are on and running. A generator that goes up to 50 Amps would be able to handle this load without an issue.

Keep one thing in mind when you are making these calculations: you might not always have each appliance running all the time. Using our examples above, the microwave will only use 8.33 Amps while you have it running to heat things up. When it isn’t running, there is no power usage. That is why there might be times when you want to run the microwave, so you will have to turn off another circuit. Then turn on the microwave circuit, run it to heat whatever you need, then you turn it back off again to use a different circuit.

Hopefully your power won’t be out more than a day or two so you will be able to manage cycling between circuits without too much trouble.


Is there room in my electrical panel?

As discussed above, you will need space in your electrical panel for a new 30 Amp or 50 Amp breaker, depending on the generator you choose. You may not have enough room in your electrical panel to add a new circuit and breaker for this. Every panel is different, so the best thing for you to do is call us and have us take a look at your system. After we look at it, we can advise you on your options and give you an estimate of what it will cost to get your new generator wired for future use.

why should i hire a master electrician