Switches are used throughout homes and businesses, and perhaps most people never give it a single thought as to how they operate. That is, of course, until they fail to function. It is that sinking feeling when you flip the light switch on or running the garbage disposal in the kitchen sink and nothing happens. That is when it is handy to know that a typical light switch is a single pole single throw switch and, chances are, the operation of a garbage disposal relies on a double pole single throw switch.
The classification of a pole when used for a switch, accounts for the number of separate power conductors that can be connected to the switch. A single pole switch has only one set of contacts within the plastic insulated enclosure. A double pole switch has two sets of separate contacts for controlling the electrical power. By flipping the lever, these two contacts are simultaneously moved to the open or closed position.
All switches, regardless of the type, can only perform two functions. They can either turn electrical power on or off or divert the flow. Single throw type switches, designate an on or off type operation. Double throw switches, can divert the flow of electricity from one set of screw terminals to another. These screw terminals are mounted on the side of the switch. A double pole single throw switch is used for turning electricity either on or off.
Switches are also rated by voltage and amperage. The common rating for most switches will be 120 volts alternating current (VAC) and 15 amperes of current. Special ratings for higher powered switches, depending on voltage, may be as high as 600 VAC and 30 amperes of current. These types of switches in general, will be the double pole single throw switch. A typical application for this switch could include the power controls for garbage disposals, water pumps and home furnaces.
Double pole single throw switches are generally constructed from a heavy duty insulated plastic. The metal frame that holds the switch body to the wall mounting box, runs the full length of the switch. Attached to the metal frame is a green grounding screw that attaches the electrical systems safety ground wire. This ground wire protects the occupants and equipment from any hazardous voltage that may go astray.
All double pole single throw switches can be identified by a stamping on the switch body. The letters, DBST, will be engraved some where on the switch. Colour-coding of the screw terminals themselves cannot be accurate, as a double pole double throw switch will have the same colour coded screws. Generally this colour is a dark metallic or copper colour.
An ohmmeter may have to be used for the proper identification as to the action of the switch. When using an ohmmeter, the power must be off to the electrical circuit and all wires removed from the switch. A double pole single throw switch will show an on or off state. A double pole double throw switch will show the terminals are switched from one side of the switch to the other.