Electrical Switches



Switch Types

There are several switch types, which may be used in high pressure cleaning equipment.
These include:

· SPST – (Single Pole Single Throw). This is the most common toggle switch is like an ordinary light switch. A single pole single throw switch has one pole on each end and the switch moves between the poles in a single motion. It is a designation for the switch contact arrangement that has just two terminals. As the switch is thrown, these two terminals will be either open or closed depending on the position of the handle.
· DPST – (Double Pole Single Throw). The single throw switch type has two connection points at each end of the switch and allows for two separate circuits to be operated by a single switch. Single throw means that each switch can make or break a circuit; it can connect the input wire to the output, or not. It can’t connect to one or other of two output wires, switching between them.
· SPDT – (Single Pole Double Throw). Double throw switches have a wiring connection in the center between the two end poles. The switch may be wired with connections to the center and either end. Double throw switches are also available in a center "off" configuration.
· DPDT – (Double Pole Double Throw). These allow for operation of two circuits with the double throw switch. It is used for a disconnecting a 240 volt supply from a 240 volt load.

Rotary Switch



A rotary switch is a multi-position switch, which allows control of power to the pump and boiler using the same switch. It is operated by rotation and the switch action is progressive. (These are often chosen when more than 2 positions are needed, such as a three-speed fan or a CB radio with multiple frequencies of reception or "channels"). Turned to the first position, the switch leaves the circuit to the pump motor completed and completes the circuit to the boiler. The boiler fires and equipment is operating in hot water mode. This is the most widely used switch type in the industry. Rotary switches used in the industry are generally high amperage full amp draw. A magnetic contractor is not required with a high amperage switch.

A rotary switch consists of a spindle or "rotor" that has a contact arm or "spoke" which projects from its surface like a cam. It has an array of terminals, arranged in a circle around the rotor, each of which serves as a contact for the "spoke" through which any one of a number of different electrical circuits can be connected to the rotor. The switch is layered to allow the use of multiple poles; each layer is equivalent to one pole. Usually such a switch has a detent mechanism so it "clicks" from one active position to another rather than stalls in an intermediate position. Thus a rotary switch provides greater pole and throw capabilities than simpler switches do.

Modern rotary switches utilize a "star wheel" mechanism to provide the switching positions 30, 45, 60 or 90 degrees. Nylon cams are then mounted behind this mechanism and spring-loaded electrical contacts slide around these cams. The cams are notched or cut where the contact should close in order to make an electrical circuit.

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