Disconnect switches rapidly disconnect from power supplies in the event of an emergency. They may be categorized as fusible, non-fusible, enclosed fusible, and enclosed non-fusible switches. Fusible switches support the installation of fuses and provide a greater degree of protection. Non-fusible switches do not. Some disconnect switches are suitable for AC systems. Others are designed for DC systems. Products for single-phase and three-phase power are also available.
Disconnect switches can function in conjunction with circuit breakers, devices which interrupt the flow of electricity along a circuit when the current exceeds the circuit’s capacity. For example, a battery disconnect switch is a knife switch that prevents unwanted drain from a vehicle battery when the vehicle isn’t in use or is in storage. The battery-disconnect switch installs over either the positive or negative terminals on the battery. Another type of battery disconnect switch comes with a removable knob to protect a vehicle from being stolen when it is parked in a public garage for long periods.
Electrical disconnect switches are often used on electric motors, such as industrial forklifts, agricultural vehicles, and aircraft tow tractors. Electrical disconnect switches are also used on a variety of electrical appliances, such as heaters and air conditioners, to ensure that contractors working on these appliances are protected from the incoming power. Electrical disconnect switches can adhere to international standards developed by the International Electrotechnical Commission (IEC) or to U.S. standard developed the National Electrical Manufacturers Association (NEMA). Both regulating bodies work together to provide quality standards for electrical products manufacturers.
Selecting disconnect switches requires an analysis of performance specifications. Parameters include current rating, operating voltage, horsepower rating, short-circuit interrupt capacity, and number poles. With fusible disconnect switches, fuse type is also an important consideration. Choices include Class CC, Class H, Class J, Class L, Class T, and Class K. For both fusible disconnect switches and non-fusible disconnect switches, there are many choices for mounting style. These include DIN rail, panel mount, wall or box-mount, base mount, and flange mount.
Disconnect switches are important safety features on generators and electrical motors. Rural electricity providers or cooperatives often require customers to provide a generator disconnect switch if an auxiliary generator is operating on their system. The generator disconnect switch ensures that a lineman working on the system is in no danger of electrocution. A generator disconnect switch is also called a transfer or isolation switch.
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