How to Set Up a Portable Generator for Backup Power

Severe weather. Grid failures. Electric utility breakdowns.

Whatever the reason, when the power goes out, it’s not long before you remember just how crucial electricity is in meeting your basic needs and comfort.

More and more Texans are thinking ahead and planning for backup power during these failures. There are many ways to achieve backup power, and you should thoughtfully plan what’s best for your family and home.


Is a portable generator right for you?

There are two primary methods folks use for backup power: standby generators and portable generators.

Standby generators start up automatically during a power outage. They can supply power for most, if not all, of your home’s needs. The investment is greater, both in upfront costs and ongoing maintenance, but so are the benefits.

Portable generators are smaller, more versatile generators used in a variety of purposes. Camping, tailgating, and outdoor parties are just a few. While losing power to your home is no party, a portable generator that is properly connected to your home’s breaker box can temporarily power your essentials and some minor comforts until things are back to normal. 

The investment is still not cheap, but it’s far less than investing in a standby generator. Depending on the generator you choose, expect to invest about $2,500 for both your supplies and electrical installation.

Does a portable generator sound like the best option for you? Keep reading to decide which type will meet your needs.


A photo of a Portable Generator Inlet Box from Mister Sparky Electrician Houston.

Inlet Box for Generator Cord

How a portable generator is used for backup power to your home

To use a portable generator to power to your home’s electrical circuits in the case of an outage, you’ll need to have a qualified electrician install an inlet box that connects to your home’s electrical breaker box. Your generator cord will plug-in to the portable generator at one end, and into the inlet box at the other end.

The installation of a reliable interlock kit or transfer switch will keep your power from the utility (grid) OFF while your portable generator power is ON (and vice versa).


Interlock Kit versus Transfer Switch

There are two ways to switch your home’s power source from the electrical grid to your portable generator: an Interlock Kit or a Transfer Switch.

We generally recommend an Interlock Kit over a Transfer Switch. Why? A transfer switch setup is less flexible than an interlock kit setup. The transfer switch limits you to only select circuits, which are decided on during installation. On the other hand, an interlock kit allows you to run power from your portable generator to any circuit within the electrical panel.

There is a risk that you accidentally overload the generator because of this, but with preparation and education, you’ll be able to manage this easily and enjoy the flexibility this setup offers.


Which portable generator is right for my home?

While we do not endorse a particular brand, we do recommend you purchase a generator that can create enough power to meet your goals. In the world of generators, this is discussed in watts. We recommend you purchase a generator that can provide as many watts as possible to your home.

It’s also very important to consider the connections available on the generator. At a minimum, you need a 30amp 120V/240V outlet. Ideally, go for one with a larger 50 amp outlet. 


How many watts do I need for backup power to my home? 

Let’s start with the maximum size portable generator you can likely hook-up to your home’s breaker box, and work our way backwards. The largest inlet box and breaker for this project is 50 amps, which equates to 12,000 max watts. If you can purchase a generator this large, it will provide the most flexibility and ease while supplying backup power to your home. 

The other important consideration is how many watts you’ll need at a minimum from your portable generator at any given time. If you have too many things turned on at once, you can overload your generator and cause damage. 

Utilize a wattage worksheet to plan the total wattage of all the electrical devices that you’ll have connected at one time. Here are some you can use: 

Generac–a leader in generator manufacturing–offers the following guidance in a product owner’s manual

  • The rated wattage of lights can be taken from light bulbs. The rated wattage of tools, appliances, and motors can be found on a data label or decal affixed to the device.
  • If the appliance, tool, or motor does not give wattage, multiply volts times ampere rating to determine watts (volts x amps = watts).
  • Some electric motors, such as induction types, require approximately three times more watts of power for starting than for running. This surge of power lasts only a few seconds when starting such motors. Make sure to allow for high starting wattage when selecting electrical devices to connect to the generator: (1) Calculate the watts needed to start the largest motor. (2) Add to that figure the running watts of all other connected loads.

The wattage required varies by home and it’s important that anyone operating a portable generator takes responsibility for this calculation and the safe operation of the machine.


Running your A/C with portable generator power

Homeowners’ primary goal with backup power is to run their A/C. Of course, this is often the largest draw on the generator’s power. 

It’s important to know your A/C’s “BTU value” to estimate its starting wattage. Find the model number on your outdoor A/C unit nameplate. Search this model number on the internet to find its BTUs. 

The age and condition of your A/C will also impact how much power it needs to start-up. With this in mind, you will likely need to test starting up your A/C with your portable generator supplying power to your home.

If you have trouble starting up your A/C and it’s still fairly new and in good condition, consider adding a “compressor saver” or “soft start kit” which will reduce the power draw it requires to start-up. 


Requirements at your Electrical Breaker Box

At Mister Sparky, we look for the following features of a home’s breaker box in order to provide a safe and reliable setup:

  • Breaker box less than 15 years old – When the electrical equipment is older than 15 years, we don’t feel confident that it will be a reliable installation. Old breakers sometimes do not come back on when turned off (which you’ll do while operating your portable generator). And some of the parts we need – for instance, an interlock kit – are not manufactured for older panels. While it is possible to source a custom interlock kit, we prefer not to do this work on older panels or brands that have known hazard issues like Federal Pacific (FPE), Zinsco, or Challenger.
  • Main breaker is present – A main breaker is required in order for an interlock kit to be installed, which will keep the utility power to the home off while the generator power is turned on. (The video above explains the interlock kit and how the generator breaker is installed next to the main breaker). Most homes have a main breaker present, identified because it sits separately from the other breakers and is larger. It could also sit next to the other breakers and be labeled “Main.” The number on the main breaker handle typically reads 100, 125, 150, or 200, marking its amperage. If you don’t see a main breaker, you may have an outdoor disconnect, which is more common in new homes. In this case, an electrician would need to add a main breaker. 
  • Two extra spaces are available in the breaker box – The new breaker that will supply power from your generator to the home takes up two spaces. The breakers may need to be moved around, which is possible with spaces available. When the spaces in a breaker box are completely full, it can be possible to create space by combining breakers into a “tandem” type. An electrician would need to evaluate this for you. 


You’re Almost Done Planning Ahead… Now Get Ready!

Once the electrical installation is complete, the work is not quite done. As a proactive homeowner, you’re almost to the finish line (so don’t stop now)!

Using your pre-planned wattage worksheet, practice switching over to portable generator power and note which circuits need to be shut-off, and in what sequence you’ll keep things on or off. 

Read your owner’s manual thoroughly and become an expert on your generator’s operation. You should also consider learning about the maintenance your portable generator needs to be in top condition when you need it. You may want to use it for projects or camping to keep the components moving. After use–if you’re not using it for a while–keep it running until the gas is fully used and out of the motor. For safety reasons, we also recommend you simply stay prepared to purchase fuel when a severe weather event is on its way, rather than storing fuel at your home.