Once you have your backup generator, you need one more thing — the transfer switch. A transfer switch changes electrical power load from one source to another. In a backup generator setup, the transfer switch transfers electrical load from the main grid to the generator in case of a blackout. The reverse happens when the power comes back.

Is It Necessary?

Technically, you can connect your backup generator without a transfer switch. However, you need the transfer switch for three main reasons.

1. Safety

The absence of a transfer switch increases the risk of power back-feeding. Power back-feeding occurs if electrical power from the generator flows and mixes with electrical power from the main grid. Back-feeding can occur, for example, if you use an extension code to connect your generator to your use. Back-feeding can cause a power surge, increasing the risk of an electrical fire.

Also, extension codes are not suitable for long-term use or for powering heavy-duty appliances. For example, extension codes are not safe for heating and cooling equipment.

2. Convenience

A transfer switch is more convenient to use than other alternatives, such as extension codes. You don’t have to look for an extension code and connect it in the dark during a blackout. Just install the transfer switch and leave it in place for use after that.

3. Code Compliance

A transfer switch is legally necessary even if you disregard the danger and inconvenience of extension codes. The National Electric Code (NEC) requires an electrical code for generators. Code violation can attract legal and monetary repercussions. You might also struggle to sell a house with electrical code violations.

How Do You Select the Right One?

Now that you know why you need a transfer switch, you should know the selection criteria. Consider these factors when choosing a transfer switch.

Mode of Operation

Transfer switches have two basic modes of operations: automatic and manual.

As the name suggests, an automatic transfer switch automatically changes from the grid to the generator in a blackout. Thus, you don’t have to stumble in the dark looking for the switch if you install the automatic variety. Some automatic transfer switches are programmable — you can set them to prioritize some circuits over others.

With a manual transfer switch, you have to flip the switch to transfer power from the grid to the generator. Load management is also manual if you want to avoid power overload. Manual transfer switches are relatively cheaper than automatic transfer switches.

Power Rating

A transfer switch’s power rating is the maximum power it can safely handle. You must match the transfer switch capacity to your backup generator’s capacity. For a multi-outlet generator, the transfer switch should match the largest outlet in the generator. For example, if the generator’s largest outlet is 20-amps, get a transfer switch rated 20-amps.

Number of Circuits

Some transfer switches only handle single circuits, while others handle multiple circuits. Generators also vary in the number of circuits they have. Get a transfer switch with circuits that match the number of circuits in your generator.

Multiple circuits allow you to power multiple circuits independently. For example, you can power major appliances (such as heating appliances) and lighting systems independently. That way, a mishap in one circuit doesn’t affect other parts circuits.


Lastly, you should also get a transfer switch suitable for your installation environment. Some transfer switches are only suitable for indoor usage, while others are suitable for outdoor usage. Outdoor transfer switches can handle different weather elements, such as moisture and sunlight, without malfunctioning.

Sizing, designing, and installing backup generators require professional skills. Oak Electric has over four decades of experience in the electrical industry, including generator installation. Contact us for generator sizing and installation, and we will get back to you with an affordable quote.