Transfer Switches

Transfer switches transfer electrical power back and forth between two power systems or buses such as a utility power line and a backup motor-generator power supply. They are used in applications that require switching between two power sources. Some transfer switches allow switching from a primary to a secondary, or even a tertiary power source. Others are used to switch from a regular power source to a temporary generator. There are two basic types of products: manual transfer switches and automatic transfer switches. A combination transfer switch can function as either a manual transfer switch or automatic transfer switch, depending on the mode of operation. Generator transfer switches and bus transfer switches are also commonly available.

Transfer switches such as a generator transfer switch include a sensor that monitors current levels from a utility line. If current levels decrease unexpectedly, the sensor sends a signal to a backup generator to switch power sources automatically. This stops the power flow from the utility line and draws power from the generator. Bus transfer switches are often with dual-bus power systems. A bus transfer switch is used to monitor equipment attached to a utility line and switch the power source automatically if the primary source of current fails. In this way, transfer switches are an important part of continuous operations.

Selecting transfer switches requires an analysis of product specifications, applications, and certifications and approvals. Product specifications for transfer switches include number of poles, current rating (amps), voltage rating (VAC), return-to-utility time (sec), dimensions (in), and weight (lbs). Applications include manufacturing, material handling, and power generation. Transfer switch manufacturers are located across the United States and around the world. They conform to a variety of regulatory requirements and quality standards. Some products feature outdoor-rated enclosures that meet requirements from the National Electrical Manufacturers Association (NEMA). Others meet published safety standards from Underwriters Laboratories (UL).

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Part Numbers for Transfer Switches