A manual transfer switch requires you to start the generator and move the switch by hand to shift selected circuits to generator power. An automatic transfer switch senses when utility power fails, signals a compatible generator to start and switches the circuits over on its own.
Both keep generator power separated from the utility lines. The difference is how much you have to do during an outage.
How a Manual Transfer Switch Works
With a manual setup, you go outside during an outage, start the generator and connect it, often through a power inlet. Then you move the switch, or a set of switches for each circuit, to the generator position.
When utility power returns, you switch back to utility power and shut down the generator.
Manual transfer switches are common with portable generators. They usually cost less and involve simpler equipment, but someone needs to be home and able to operate the generator safely.
How an Automatic Transfer Switch Works
An automatic transfer switch monitors utility power. When it senses an outage, it signals the generator to start. Once the generator is running properly, the switch transfers the selected circuits, or the whole home, to generator power.
When utility power returns and stabilizes, the switch transfers back and the generator shuts down after a cool-down period.
Automatic transfer switches are typically paired with permanently installed standby generators that can start on their own. They are useful for homes where backup power must start without someone present, such as for sump pumps or medical equipment.
Generator Compatibility Matters
Not every generator works with every type of switch. Automatic switches need a generator with automatic start capability and controls that can communicate with the switch. Most portable generators are not designed for automatic transfer.
The switch must also be sized for the generator and the circuits it will serve. Some automatic systems include load management to prevent large appliances from overloading the generator.
A listed panel interlock is another manual option for some panels. It mechanically prevents the main breaker and the generator breaker from being on at the same time.
Choosing Between Them
The choice depends on your generator, your budget, which circuits you need to back up and whether backup power must start automatically.
A manual switch may suit a homeowner with a portable generator who wants to power a few important circuits during occasional outages. An automatic system may suit homes with frequent or longer outages, or where someone depends on uninterrupted power.
Both types involve the main panel, generally require a permit and inspection in Denver and should be installed by a qualified electrician.
If you are deciding on transfer equipment, our transfer switch installation page explains the options. Contact us with your generator details and the circuits you want to back up, and we can help you compare the setups.