The installation requirements for a shallow electrical box 2-gang include ensuring it is securely mounted to a stud or other support, providing enough space for the wires and devices to fit comfortably, and following all local electrical codes and regulations.
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All of these types of devices have different applications and usually are of different physical sizes. If you are talking about poles and confusing it with gangs then; A 2 pole is a double pole single throw switch. A 3 pole switch is usually used as a manual transfer switch for three phase applications. A 4 pole, never heard of one. A 1 way or single pole switch is the same type of switch used in home circuits to turn the lights on and off. The term gang in the electrical trade refers to electrical junction boxes (usually for switches) that are joined together to make an installation compact by keeping all of the switches in a common place. A single "hot" circuit is brought in from the distribution panel and pigtailed to each individual switch. The bottom of the switch then connects to the individual lighting loads.