Yes. A light switch may be used as a disconnecting means if it fits the standards for a disconnecting means outlined in the National Electrical Code (NEC), NFPA 70-2005. As a result, for the purposes of Subpart S, a light switch can often serve as a disconnecting mechanism.
However, the NEC requires that all disconnects be listed as part of the circuit's wiring system. This includes any switches located within the electrical box they are attached to. Light switches do not qualify as separate disconnects because they cannot be tested easily or by sight. If a light switch were to fail prematurely, you would have no way of knowing unless you opened up the wall paneling or some other part of the house.
The best way to ensure a safe disconnect is through the use of a dedicated disconnect. These devices can either be built into an outlet or include only a lever or button that must be pressed to break the connection.
Disconnecting circuits at the source reduces the risk of electric shock. It also helps prevent unnecessary power consumption when one branch of a three-way circuit is not being used.
A disconnector, disconnect switch, or isolator switch is used in electrical engineering to guarantee that an electrical circuit is totally de-energized for servicing or maintenance. Disconnect switches are usually designed with two positions: "on" or "off." When the switch is in the "on" position, all power flows through it from source to load; when the switch is in the "off" position, no power flows through it from source to load.
Disconnectors can be found in many different products, from small household appliances to large industrial machinery. They are also used by electricians when repairing wiring systems to prevent any electricity from flowing through the repaired section of cable. The absence of voltage across the disconnected wire prevents any damage to connected equipment due to electricity flowing even when not needed. Disconnecting wires are always black or red with white tape to indicate which circuit they are part of. Other colors may be used as well depending on the application. A green disconnect indicates a hot conductor is present while a yellow one means the line is live and should not be touched.
In general practice, a disconnect switch must be able to handle at least 15 amperes of current and have a thermal rating equal to or greater than the expected maximum current through it during its normal life span (usually between 10,000 and 20,000 hours).
Doing the switch is fine as long as whomever wired it places the switch on the circuit's hot leg. A switch will work properly to turn on and off a light from the other leg, which some people refer to as the common, neutral, or white wire. The black cable should carry power or heat. If it doesn't, there's a problem that needs to be fixed by a qualified electrician.
If you're sure you know what you're doing and have the required tools, then by all means give it a try. Just make sure you don't leave the room or touch anything else in the house while you're working on the wiring.
The best way to check if you've got the correct wiring at a location other than where the switch resides is to use a voltage tester. These devices check each conductor for voltage to determine whether it is hot, neutral, or ground. Without going into too much detail, voltages are measured between two points separated by either conductor; one point is attached to a terminal of the meter while the other is connected to the opposite terminal. If no voltage is present, then both wires are likely hot; if voltage is present but not enough to turn on any lights, then at least one of the wires is likely neutral or ground. A third possibility is that one wire is hot while the other is dead, in which case it should be removed from service before changing out the switch.