I recently mapped every appliance, receptacle, light fixture, switch to their respective breaker in the master 200A electrical panel. When I was finished I ended up with 2 20A breakers that did not go to anything I could find. The breakers were on when we bought the house. I have since shut them off not knowing what they go to.
Is there any other way to trace them or should I just not worry about them and leave them shut off?
Short of buying and using a tracer, I'd check for:
Lastly, if you turned off just these circuits to see what stopped working, do the reverse. Turn everything else off except the one circuit. It's entirely possible that someone bridged two circuits together somewhere.
The location in the panel may give you a clue. Similar appliances are often grouped near each other, and additions tend to be added to empty spaces at the bottom.
It is always possible that the two extra breakers and circuits are spares that were wired in. Sometimes, particularly when some circuits are added after the initial building construction, it is cost effective to string extra wires from the electrical panel to a more centralized and easily accessible location.
The most obvious thing to find out where these two circuits connect is to suggest that you follow the two black wires from those circuit breakers to where they exit the breaker panel. Then continue to trace them to where they are routed through the framing of the building. This of course gets complicated fast when the wires are not visible and are covered over by wall and ceiling materials.
One clue that can be worth considering is if the two circuits are wired up with wiring that looks different from the rest of the installation. You may find for example that, if Romex was used, that the wire jacket is a different color or is stamped with a different label. You can then enter spaces such as attics, crawl spaces, unfinished garages or unfinished utility areas of the house to see if you can spot these particular wires being routed through that area.
Another thing to consider, especially if this house was built from a very standard plan, that it is possible that the extra circuits were installed at the time of original construction. They may have been to support some building option that ended up not being selected by the original owner. Some items like this could be wiring routed to near a fire place, wiring to lamp post locations out at the end of a driveway, wiring installed for a dishwasher when none was ever actually installed.
There are also circuit wiring tracer devices available that inject a signal into the wiring and than supposedly allow you to trace wires using a pickup probe that is near the wire. I have found that these do not work very well because the close proximity of all the wires in the main panel causes the signal to couple into many of the other wires as well. It is possible that a more expensive tracer may be more effective than the lower cost one that I have used.
I have not yet figured out what circuit my smoke detectors are on after 3 years in this house. I had mapped out the entire box early on, but only recently thought of those. They MUST be on a shared circuit, because every breaker has some function attached to it. However, yours may be dedicated to those detectors.
