A load break switch is a disconnect switch that has been designed to provide making or breaking of specified currents. This is accomplished by addition of equipment that increases the operating speed of the disconnect switch blade and the addition of some type of equipment to alter the arcing phenomena and allow the safe interruption of the arc resulting when switching load currents.
Disconnect switches can be supplied with equipment to provide a limited load switching capability.
Arcing horns, whips, and spring actuators are typical at lower voltages. These switches are used to de-energize or energize a circuit that possesses some limited amount of magnetic or capacitive current, such as transformer exciting current or line charging currents.
An air switch can be modified to include a series interrupter (typically vacuum or SF6) for higher voltage and current interrupting levels. These interrupters increase the load break capability of the disconnect switch and can be applied for switching load or fault currents of the associated equipment.
In industrial applications, a medium voltage fused load interrupter switch is most frequently used as the primary disconnect for a load center substation transformer. A load interrupter switch is well suited to this application, as load currents are low, switching is infrequent, and remote control is not ordinarily needed.
The table below shows the major characteristics of medium voltage load interrupter switches that influence the application. Of course, the table entries are generalized, and the information varies by the voltage and current ratings of the equipment. This is particularly true for interrupter switches, where the endurance capabilities vary greatly according to the ratings. However, the table is valid for an overall understanding.