Buyers Guide to Transfer Switches

Transfer Switches Work With Standby Generators To Supply Electricity When You Need It Most

Residential Automatic Transfer Switches make a permanent connection between your home and the standby generator. Protecting your home, generator, neighbors, and utility line workers. Transfer switches work with standby generators to supply electricity when you need it most. Within 30 seconds or less, your critical circuits will power on as if nothing ever happened.

Midwest Electric & Generator provides the correct transfer switch required for your generator installation. There are many configurations possible and making a selection is not always straightforward. The expert generator technicians at Midwest Electric & Generator make this part simple and easy to understand.

Most Common Generator Transfer Switch Types: 

Whole-Home Transfer Switch 

This transfer switch supplies the entire main breaker panel with electrical power during an outage.

Generator Sub-Panel Transfer Switch

A generator sub-panel transfer switch supplies a sub panel with a limited number of circuits during a power outage.

The sub-panel and transfer switch are usually combined into a single unit.

Service Rated Load Center Automatic Transfer Switch

This transfer switch takes the place of the main panel and incorporates the main disconnect.

Whole-Home Transfer Switches

The Whole-Home transfer switch installs between the utility meter and the main service panel. When a power outage occurs, the automatic transfer switch disconnects the incoming utility service, then connects the standby generator. The switch makes an intelligent choice about which electric supply to use. The utility is the preferred choice. When utility power is unavailable or unacceptably low, the whole-home transfer switch automatically chooses standby generator power after the generator starts and is ready to accept the load. In less than 30 seconds after the outage occurs you can expect power to be restored!

The main service panel the automatic transfer switch supplies will determine the transfer switch’s rating. A main panel with a 200-amp main breaker requires a 200AMP whole-home transfer switch. A 100-amp main breaker requires a 100AMP automatic transfer switch.

Service Entrance Rated

A whole-home transfer switch with a Service Entrance rating means that the automatic transfer switch may serve as the primary disconnect for the home’s utility service. The automatic transfer switch includes a circuit breaker that turns off the utility service to the home.

All homes are required to have a primary disconnect. Sometimes this is a fused switch located near the utility meter. In this configuration, the main panel might not have a main breaker, and turning off the power requires turning off the disconnect switch. Other homes have a main panel that includes a main circuit breaker as the primary disconnect.

A backup generator automatic transfer switch installed for use as a whole-home transfer switch requires a service entrance rating or a separate, primary disconnect located on the utility side of the switch.

Power Management

A GeneratorAutomatic Transfer Switch with Power Management allows a standby generator with less lower capacity to supply a home with a number of high-voltage loads such as air conditioners, water heaters, dryers, well pumps, electric ranges, and other 240-volt appliances.

Some appliances use large amounts of power and could overload a standby generator if too many are operating at the same time because a generator supplies a limited amount of power. For example, a 20-kilowatt standby generator can supply a maximum of 20,000 watts continuously. If another appliance added to the load exceeds 20,000 watts, the generator’s main breaker may trip and turn off power to the entire home.

Large appliances such as central air conditioners use large amounts of power. A 3-ton AC unit uses approximately 3500 watts which varies dependent on efficiency. In a home with two AC units to total power requirement is 7000 watts, plus the starting watts required to get them started. With both running at the same time, the generator may not have the power to supply everything else.

Power Management Options allow the transfer switch to manage the power. If one AC unit is running, the second may have to wait for the first one to finish before it starts. If the home is using very little power when both units start, power management may allow both to start and run at the same time. The benefits of using power management include a lower initial cost for the home generator with an automatic transfer switch and reduced fuel costs any time the generator operates.

An automatic transfer switch with power management may prioritize heavy loads. The AC and well pump might have first priority while an electric water heater and dryer have a lower priority. Lower priority loads wait for higher priority loads to finish or until additional power becomes available.

Some high-voltage loads operate via a low-voltage contactor such as a thermostat for a furnace and air conditioner. The thermostat turns the furnace and air conditioner on and off by opening and closing low-voltage relays that control the high-voltage current. Many whole-home switches with power management capability include the means to operate these loads.

Other high-voltage loads such as hot water heaters and dryers simply switch on and off. They require a different strategy for managing power use. A relay module, sometimes called a Power Management Module, is controlled by the automatic transfer switch to turn the power on and off to the appliance.

Backup Generator Sub-Panel Automatic Transfer Switches


A Sub-Panel Automatic Transfer Switch installs between the main service panel and the loads it controls. Under normal operating conditions, the automatic transfer switch is supplied with power from the main service panel through a circuit breaker located in the main panel. During a power outage, the generator sub-panel automatic transfer switch disconnects itself from the main panel and connects to the standby generator to supply its circuits with electrical power.

The circuit breakers for the circuits served by this type of automatic transfer switch are located in a generator sub-panel. The automatic transfer switch supplies the circuit breakers with power from either the main panel or from the generator depending on the current state of the utility power.


Indoor or Outdoor Rated


Residential automatic transfer switches are rated for inside only or outside and inside usage.

Automatic Transfer Switches with a NEMA 1 rating is for indoor use only. It is only suitable for use and installation in dry areas. They are protected against an accidental indirect splash, however. The enclosure is not watertight and will not keep the elements out. The primary function protects against accidental contact with electrical parts.

Automatic Transfer Switched with a NEMA 3 rating allows for either indoor or outdoor installation. This transfer switch is water-resistant and suitable for use in a location where it is exposed to rain, snow, and ice. Some indoor installations such as a laundry room require a NEMA 3 rating when exposed to condensation or splashing water is possible.


Automatic Transfer Switch Load Center

Instead of installing a separate sub-panel served by a backup generator automatic transfer switch, the Load-Center Automatic Transfer Switch incorporates both into the same electrical box which saves space and simplifies wiring.

A load center automatic transfer switch may have only a few circuits or many. 8, 10, 12, and 16-circuit configurations are common. An automatic transfer switch load center sold as a Pre-Wired Transfer Switch may come with the circuit breakers installed and will include the wiring necessary to connect it to the main panel and the standby generator. Purchasing a pre-wired transfer switch ensures using the correct wire gauge for each circuit and eliminates or reduces the need for purchasing spooled wire.

The number of circuits available refers to the number of single-pole (120-volt) circuit breakers it can accommodate. Double-pole (240-volt) circuit breakers require two spaces. Double-pole breakers look like a pair of single-pole breakers with the switch handles connected. An electric dryer (240-volts) will require two spaces for a double-pole, 30-amp circuit breaker. The kitchen refrigerator circuit (120-volts) will only require one space for a single-pole 15- or 20-amp circuit breaker.

Some circuits require special breakers. AFCI and GFCI breakers usually require a separate purchase and installation. Midwest Electric & Generator supplies all special breakers made by the correct manufacturer and of the correct type. Some breakers have special wiring requirements.

Service-Rated Load-Center ATS

A Service-Rated Load-Center Automatic Transfer Switch can replace your home’s main service panel. The main circuit breaker inside an automatic transfer switch load center acts as the service disconnect. The transfer switch mechanism connects to the utility meter and to the standby generator. Breakers serve the branch circuits in the same manner as the breakers in a regular main service panel.

This type of automatic transfer switch load center is a good choice for including a standby generator in the design of a new home. No additional wiring for a generator sub-panel or separate load center automatic transfer switch is necessary. It is already included in the installation and there are no electrical boxes to figure out where to locate.

Another possibility incorporates the Service Entrance-Rated Automatic Transfer Switch Load Center into a service upgrade. Older homes often have limited utility services. A new main service panel is required for an upgrade to meet newer building codes. Incorporating a standby generator installation in the upgrade is easy and reduces future costs because an electrician doesn’t have to take the current wiring apart to install a new transfer switch.

Ready To Book Your Free Estimate?

Now that you know a little more about how  Transfer Switches work with standby generators to supply electricity when you need it most work with the automatic standby generator, let’s book your FREE ESTIMATE! 

Whether you are looking for a portable gasoline generator, a home standby generator, or even a commercial or industrial generator, Midwest Electric & Generator makes the process simple!

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We at Midwest Electric and Generator, Inc are the leading Generator Experts, actually, generators are all we do. New to the whole generator thing? No worries, we are here for you, your family and business. 


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