Another is that the box is on a circuit three way switch loop. Or it could be the red wire is the wire going to the fixture and the black wires are the live wires.
3 Way Switch Wiring Electrical 101
What is the red wire for. In most cases you see a red wire in an outlet box only in special circumstances. One is that the outlet is a 240 volt one which requires an extra hot wire. In standard 120 volt wiring the hot wire is black but it can also be red. A live black wire a green or copper ground wire and a neutral white wire. Red electrical wire indicates the secondary live wires in a 220 volt circuit used in some types of switch legs and in the interconnection between smoke detectors that are hard wired into the power system. It could be there is or once was a three way switch in play.
If the wire still is hot the wire is a hot wire that delivers electrical power to the branch circuit. Well cover the easier scenario first. The red wire is for the light switch. How to replace an electrical outlet 0000. This configuration sometimes called a half hot or split tab outlet is becoming increasingly popular so its good to know how to wire it. In most cases a red wire present in an electrical outlet means that a switch can operate the outlet.
Generally electrical socket boxes come with three wires each of them colored differently. When you see a red wire in a 120 volt duplex outlet box its usually because one of the outlets is operated by a wall switch while the other is always on. You can connect a red wire to another red wire or to a black wire. When you see a red wire in a light switch box it can mean two things. If turning the switch off turns the wire off the red wire delivers power from the light. A red wire in an electrical outlet often indicates a second positive live wire.