Guide to Generator Transfer Switches

What is a generator transfer switch?

Both portable and standby generators can keep you and your family comfortable and safe during a power outage or emergency. Without a generator transfer switch, however, generators are difficult and often dangerous to use. A generator transfer switch allows you to automatically or manually transfer your home’s power source from the electrical grid to the generator when the power cuts off.

Stationary backup generators are installed with an automatic transfer switch, but portable generators require a separate manual transfer switch. Each has advantages and disadvantages. Though an automatic transfer switch is more expensive, it is more convenient for the homeowner because it works automatically and is installed by the electrician along with the generator itself. A manual transfer switch is cheaper, but it must be installed separately and may be a hassle to switch on and off during an outage.

Whether you purchase an automatic or manual generator transfer switch, there are a number of factors to consider before you make your purchase, from the type of generator you own to the sizing of the transfer switch. Before you buy a generator or a transfer switch, you’ll also need to understand the electrical needs of your home. At AlltimePower, we’ve created a generator sizing tool to help you do just that. We’ll also be able to match you with generator dealers based on your power needs and budget.

Automatic transfer switches

Stationary backup generators are connected directly to the home’s circuits when installed by a qualified electrician. Stationary backup generators have the advantage of providing a more consistent and long-lasting energy supply to the home. Additionally, they come with a built-in generator transfer switch that automatically transfers the home’s power source from the electrical grid to the generator. You won’t have to worry about installing the transfer switch or turning it on manually during every outage. For many homeowners, this convenience and peace of mind is worth the extra cost.

An automatic standby generator transfer switch continually monitors the incoming electricity flow from the electrical grid. When it senses that the electrical flow has been interrupted, it immediately signals the generator to start. Once the generator is ready to supply power, the transfer switch cuts off the home from the electrical grid and connects the generator to your home’s electrical circuits. This whole process takes only a few seconds.

When the transfer switch detects that the electrical current has returned to its normal voltage, it transfers the electrical load back to the utility line, cutting off the power from the generator. The generator continues to run at a slower pace for a few minutes to cool off the engine. As soon as the next outage strikes, the transfer switch will be ready to switch power back to the generator. This process ensures the home maintains a continual power supply, regardless of what is going on outside the home.

Portable transfer switches

Manual generator transfer switches get the same result as automatic ones but require the homeowner to manually switch the power supply from the electrical grid to the generator. Most often, portable generators, which are not directly connected to the home’s electrical circuits, have a manual power switch. Though manually switching the power requires an extra step, it should take no more than a minute or two if the transfer switch is properly installed.

Manual power switches can either be installed inside or outside depending on their NEMA rating. During an outage, you will need to plug the generator into the inlet box, turn on the manual transfer switch, and then turn on the portable generator. After a few seconds, the generator should supply the home with power. After the outage, you’ll need to turn the switch off again, unplug the generator from the inlet box, and turn off the generator.

Depending on the electrical capacity of your portable generator and transfer switch, you may not be able to power all of the devices in your home. The generator’s power output determines the number of circuits you can power. Most 5,000 watt generators can power 6 circuits, while larger generators may be able to power 10 or more circuits. To conserve energy, consider using only more important appliances, such as water heating and air conditioning, while waiting to run the dish washer or dryer until the power outage is over. Attempting to power too many circuits risks overloading the transfer switch and damaging the generator.

The importance of a generator transfer switch for portable generators

Though it is possible to run electrical devices using a portable generator without installing a manual transfer switch, a switch is much safer and more convenient. Running without a switch requires connecting each electrical appliance you want to run to the portable generator with an extension cord. Not only is this inconvenient and time-consuming, but it may require you to leave open windows or doors, posing a security risk to the home.

To top it off, the National Electric Code requires portable generator owners to have a properly-installed transfer switch before using the portable generator. This is because connecting portable generators directly to appliances increases a homeowner’s risk of accidents. If you connect the generator to your home’s electrical devices with extension cords, the power from the generator will not automatically switch off. Instead, the power will go back down the line to the generator. This may damage the generator and the appliances connected to it and could even cause a fire or electrocution. It’s better to plan ahead and buy a transfer switch along with the portable generator.

Sizing a generator transfer switch

Before you buy and install a transfer switch, you’ll need to determine the size or amperage you’ll need. The amperage refers to how much electrical current the transfer switch can safely or accurately handle. When you start to shop for a transfer switch, you’ll probably see different amp ratings. This shows how many amps the transfer switch can handle. For example, if the transfer switch can handle a maximum of 50 amps, its size will be listed as 50 amps.

The best way to determine the ideal size of your transfer switch is to match it to your generator’s load. To do this, you should match the largest outlet on your generator. For instance, if your generator’s largest outlet is 30 amps, you should buy a 30-amp transfer switch to get the full power load. If you are unsure how much electrical output you need from your generator, you may want to consult our generator sizing calculator. This will get you on the right track to buying the ideal generator and transfer switch.

Even if you properly match the size of the transfer switch to that of the generator, you should be careful not to overload the system by supplying too much power at once. Some power meters include built-in wattage meters that keep track of what is being powered. This helps you prevent overloading the system and accidentally damaging the generator and appliances.

Choosing the right generator transfer switch

Even after determining whether you need a manual or automatic transfer switch and finding the right size, there are a number of other factors to consider. For example, transfer switches can be single-circuit, dual-circuit, or multi-circuit. A larger generator and higher home power usage mean you may need multiple circuits, while a smaller generator and lower home power usage mean you may only need a single- or double-circuit transfer switch.

Additionally, most transfer switches are designed to be installed either inside or outside the home. Outdoor transfer switches come with a NEMA 3R designation, which means they are able to withstand various weather conditions without sustaining damage. You can also choose to buy a pre-wired transfer switch, which is more expensive but easier to install, or a switch that does not come pre-wired.

Installing and using a transfer switch

An automatic generator transfer switch should only be installed by a qualified professional electrician. A manual transfer switch can be installed by a well-informed homeowner, but we recommend consulting your owner’s manual. We can only provide a general guide to installing the transfer switch. For a more comprehensive explanation, check out Electrical Engineering Portal’s installation guide. If you choose to install it yourself, be sure to follow the necessary safety precautions and code regulations for your home.

When installing a manual transfer switch, you’ll want to securely mount it to the wall near the main electrical panel box. This box is usually located in the basement or garage. Next, turn off the home’s power and properly connect the transfer switch wires to the breakers in the panel box you want to control. Run an electrical cable from a receptacle in the panel box to the transfer switch.

To test your work, leave the power in the home off. Plug the generator into an electrical receptacle on the transfer switch. Flip the transfer switch from “line” to “generator.” Then, turn on the portable generator. If the connected circuits are receiving enough power from the generator, the power in your home should come on. If everything works, turn the switch back to “line,” unplug the generator, and turn the generator back off. Congratulations! You are ready for the next outage.

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