Indexing a panel is not hard, but it is easy to do loosely — and a loose index helps no one, least of all a future owner. The discipline is this: know everything that can draw power, decide a single method for finding which breaker feeds what, and label in terms that outlive the current occupants.

First you need — for your own sanity — to list each and every electric item in or around your home. You are not going to find that each circuit corresponds exactly with a nameable room. So you need to think in terms of each receptacle, each light, and each built-in appliance. And don't forget things like wired smoke alarms, a security system, the doorbell, a furnace, electric heaters and water heaters, pumps, lights under the house or in an attic, outdoor and garden lights and receptacles, and things controlled automatically (by thermostats, photocells, motion sensors, and timers).

Second, you will need ways to determine whether each of the things listed is receiving power or not. Using a portable lamp or nightlight makes sense for receptacles, and switching most permanent lights on or leaving their switches on makes sense (if your light bulbs are all functional). But other items may take more doing; think ahead about this.

Choosing a method

A common reasonable procedure for determining which things a given circuit consists of is to turn off a single breaker and then go check for what is dead. This will work if you are sure to check everything in the house for deadness. Another way is to turn everything in the panel off and then turn on just the circuit to be described. This method forces you to see signs of life in a thing before listing it, and, you still need to check everything in the house. In both cases, after you have listed everything in the first circuit or two, the number of remaining things to keep checking gets smaller. Decide which one method you will use and stick to it.

Uncommon results

You might encounter some uncommon results. If there are items which will not turn off for any one breaker (or which turn on for more than one), some kind of miswiring has occurred and needs correcting. Another thing to look for would be if one of the large "double" breakers turns off (or on) quite a few lights and receptacles (one-third of the house or more). This may indicate either:

1. that this breaker is a "submain" (and needs that label) and simply sends its power to most of the single breakers in the panel; or
2. that it is feeding a "subpanel" (which has a number of circuits of its own) elsewhere in the house, which you should locate and should label as well; in this case, the double breaker at the main panel should only be labeled "Subpanel", also telling its location.

Labeling that lasts