We are replacing some older outlets in our home with newer, more modern outlets. In one room, we found that two of the old outlets have two hots: a black and a red wire. The tab has been removed on the hot side to make these "split-tab" outlets.
I'm used to seeing this configuration to make a "half-hot" outlet, where one half is switched with a light switch, etc. But in this case we can't find a switch that controls the red wire.
The red hot wire loses current when we cut power to the breaker that the black wire is on, so I believe this means they are on the same breaker. However opening the breaker box is a bit beyond my comfort zone.
What else would an hot red wire be for in a split-tab outlet? If we're not using any switch for these outlets, should we just cap the red hot wire off, or should we replace with the same configuration even though we can't verify the source of the red wire?
This is 120v, in the USA.
Best Answer
Fundamentally, the color codes are
That is it. That is the whole of NEC color coding.
Therefore, black and red are functionally equivalent. Both are hots, and can be anything.
Sometimes it is are precisely nothing - just another hot. It might be always-hot while black is being used for switched-hot for instance (ugly, but legal).
It might be a former switched-hot that has been deprecated.
It might be a switched-hot actively in use. Red is a preferred wire color for switched-hot.
It could be half a multi-wire branch circuit, as discusse in another answer.
In practice, in cable it will tend to be either an MWBC or a switched hot.