A split electrical outlet is an ordinary outlet that has the brass connection tab removed between the two hot terminals. This allows the outlet to have two distinct feeds, one for the top plug-in receptacle and one for the bottom.
Purpose of a Split Electrical Outlet
There are several reasons this might be done. For example, it could allow you to have one-half of the outlet remain "hot" at all times for plugging in appliances, while the other half could be controlled by a wall switch—for controlling a desk lamp or some other light fixture. Code requires that all rooms have switchable lighting, and in a room where there is no ceiling fixture, a split receptacle offers a way to meet code requirements.
Applications for Split Outlets
Another application for split receptacles is to wire them so that they are fed by different electrical circuits—as is sometimes done in kitchen wiring, where one small appliance circuit controls the top receptacle in each outlet, while another small appliance circuit controls the bottom receptacle in each outlet. This leads to one of the cautions. This is seen less and less often due to the requirement that all countertop outlets must be GFCI protected and the shared neutral causes an issue in this case.
Precautions to Take
All outlets in your home are fed via circuits controlled by a circuit breaker in a circuit breaker panel. Normally, both halves of any outlet are on the same circuit and are fed from one circuit breaker, but that may not always be the case. This is the biggest danger when dealing with split outlets: you think you have turned off both receptacles when one is fed by a different circuit. The safety measure here is to always check to make sure the power is shut off to both halves of an electrical outlet before working on it.
The National Electrical Code now requires that the two hot wires in a split receptacle must be connected to a double-pole circuit breaker, so that when the breaker is shut off, the action will automatically disconnect both receptacles. That way, the outlet will be safe to work on. Keep this in mind whenever you are planning the installation of a new circuit with split receptacles.
If a split receptacle is wired with two individual circuit breakers, there is the chance that one breaker might be left on, creating a dangerous hazard to anyone working on the outlet. As with all code requirements, the double-pole circuit breaker is designed to save lives.