It’s not unusual for an old house to have an old doorbell lurking about somewhere that hasn’t worked in years. Fortunately, it’s likely a simple matter to get things back in working order. As illustrated in the above diagram, the parts of an old doorbell circuit include the bell, a button mounted at the door, and a battery somewhere in between the two.
Here 3-wire cable serves a split receptacle. The bottom half of the receptacle is controlled by a switch and the top half is always-hot.
The wiring in this diagram is for adding a new light fixture to a switched receptacle, i.e. one that is hot only when a switch is on. These are commonly used to turn a table or floor lamp on and off from a wall switch.
This circuit breaker wiring diagram illustrates installing a 50 amp circuit breaker for a 240 volt circuit. The 6 gauge cable for this circuit has 3 conductors and 1 ground. A 50 amp circuit like this is used for clothes dryers and new kitchen range installations.