How transfer switches work and why they must be used?

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Working principle of automatic generator and transfer switch system


Fully automatic transfer switches monitor input voltages from utility lines 24/7. When the mains fails, the automatic transfer switch will immediately sense the problem and instruct the generator to start. Once the generator is operating at the appropriate speed, the automatic transfer switch will safely shut down the utility line and open the generator power cord from the generator. Within seconds, your generator system is powering critical emergency circuits in your home or business. The transfer switch continues to monitor utility line conditions.


When the automatic transfer switch detects that the utility line voltage has returned to a steady state, it switches the power load back to the utility line and restarts monitoring for subsequent utility losses. The generators will continue to run for a few minutes for the engine cooling period while the entire system prepares for the next outage.


There are other reasons to use transfer switches. If you install a generator without a transfer switch, your fire or homeowner's insurance may fail because these switches are required by building code electrical codes in most areas. The following information explains why additional information about the transfer switch is needed. Never connect a generator through a dryer plug or socket in a building. You could start a fire or electrocute someone!


It must be installed by a qualified electrician or knowledgeable person and must comply with all applicable laws and electrical codes.


Use transfer switches When connecting to a building's electrical system.


Transmission switches protect line personnel


Utility line voltages are usually "stepped down" through transformers before entering the building. A transformer can work in reverse when the voltage passes through it in the opposite direction and "boosts" the voltage. This increased voltage, fed back through the utility line, may electrocute workers in contact with the utility line.

A properly installed transfer switch can protect the linesman


Changeover switches protect the home


An incorrect connection may short-circuit the current from the generator with the utility line current when power is restored. This could cause the electrical system to catch fire. Properly installed transfer switches can protect your home or business


The transfer switch protects the generator when power is restored, an incorrect connection can cause the current from the generator to short circuit the current from the utility line. This can cause the generator to explode or burn.




Protective electric generator


Properly installed transfer switches can protect your generator.

The generator can use many types of transfer switches. We sell portable and small generator transfer switches as well as large/industrial generator transfer switches.

Portable generators for applications where only some homes or businesses have emergency power available; We provide small transfer switches as described below. These switches have a power limit of 21,000 watts (21 kW) and are usually switched manually.


The following information gives specifications and some advice on matching the conversion switch to the generator. All the transfer switches we carry are certified. We have detailed descriptions and tables for each type of switch. If you don't find what you need, please ask us. Please go to the Small Transfer Switch page for details and the many models we offer.


For small and portable generators


The transfer switch isolates the selected circuit from the home by an "open" and then "close" switch. Each switch has 3 positions; LINE, OFF and GEN (generator). At the LINE location, the mains supply power to the selected circuit. At the GEN location, the generator supplies power to the selected circuits. To switch from LINE to GEN, the switch passes through the OFF position. This allows a positive interrupt to occur, thereby preventing sparks, arcing, or short circuits that may arise when the positive interrupt is not part of the system.

A separate circuit protector protects each selected circuit from overload. This allows the larger generator to be connected to the transfer switch without the transfer switch being overloaded.


For large/industrial generator change-over switches


Suitable for large or industrial generators and applications where emergency power is available to all homes or businesses; We supply large/industrial transfer switches. These switches can handle a variety of voltages and are usually available in unlimited sizes. These switches are usually automatically converted and have a wide range of features, including automatic excision, variable start and stop delay times, variable cooling times, and other features.

Transfer switches are available with fuses and circuit breakers. Special switches can be used to allow multiple generators to be used at once, switching between multiple generators and other situations.




Residential, commercial, industrial


30 amps to 3000 amps, open, closed, automatic and manual


Critical and distributed power sources


30 amps to 4000 amps, enclosed, automatic and manual


Soft loading


150 amps to 4000 amps


We offer many types and sizes


Indoor, 3 amps to 4,000 amps


Outdoor, 25 to 6300 amp parallel panels automatic and manual


For large industrial household and commercial generator transfer switches isolate the entire electrical service panel. Most state electrical codes require building service and transfer switches to be the same size. If the building has 200 amp service, the transfer switch must also be 200 amp. This is true even if the generator has less amperage than the building service.


Most electrical codes also require that the total load of the building cannot exceed the total load that the generator can support. This means that if the generator is "online," you may have to install equipment that prevents certain circuits from being used.


For all these cases, you should use the services of a qualified electrician. Improper device wiring may result in fire, explosion, serious injury, or death.


Large industrial change-over switches have an automatic mode that switches the change-over switch and starts the generator during a power outage, then stops the generator and switches the change-over switch again when power is restored. They also have an "off" mode, so the generator does not start automatically.


Each switch type and brand has its own features and options. We produce only top brand switches, quality comparable to ASCO, Generac, Kohler, Onan and Zenith. Our products are of high quality and proven to be reliable on the spot.


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