All About Transfer Switches

Traffic control for home generators

Transfer switches provide a critical link between home power generators and their useful applications in emergency situations. When bad weather or other conditions interrupt power service, homeowners often find themselves without the electricity to produce basic human necessities such as light, heat, and refrigeration. While stopgap safety items like flashlights, glow sticks, and fireplaces can fill some of these functions, most appliances can’t operate until full power returns.

The situation can become life threatening after a prolonged period, particularly if electric pumps, refrigerators, or climate control are compromised. Emergency backup systems currently available on the market make it possible for homeowners to have continued access to electrical service during power outages. These systems consist either of gas-powered generators or battery-based storage systems.

Transfer switches allow switching from a primary power source to a secondary or tertiary power source and form a critical element of a home’s backup power plan. Most often transfer switches can be seen where emergency power generators are used to back up power from the utility source. The transfer switch allows switching from utility power to emergency generator power.

Switches come in three varieties: manual, automatic, or combination. During a power outage, a transfer switch isolates the emergency circuits from the utility line. This allows for efficient operation of the generator without backfeeding. Like a traffic cop, the transfer switch makes sure the home system runs off either generator power or mains power, but never both.

Varieties of transfer switches

Break Before Make Transfer Switch: Breaks contact with one source of power before it makes contact with another. It prevents backfeeding from an emergency generator back into the utility line.

Closed Transition Transfer Switch (CTTS): Provides seamless transfer switching in less than half a cycle.

Soft-loading Transfer Switch (SLS): Uses CTTS technology but actively changes the amount of load accepted by the generator.

Depending upon the amount of energy needed in the event of loss of power from the grid, whether cutover is manual or automatic, and many other factors, the cost of these systems varies wildly, but the transfer switch itself is inexpensive. While pre-engineered systems are certified to comply with most local standards, a licensed electrician or technician may be required for installation. Consult local authorities for any code requirements.

More information on transfer switches