Let’s say you have an older house. Maybe the laundry room used to be in the basement but got moved to the main floor later. Then someone added a bunch of can lights in the kitchen and family room. Over time, various owners enclosed the porch, converted two bedrooms to a primary suite, and made a bunch of smaller changes, too. For a house with a few decades of such changes, the electrical system can become a mess. If you have an older house, are the breakers in your electrical panel all labeled completely and accurately?

I basically just described my house. Built in 1961, it’s gone through a lot of changes over the years. I can see the remnants of these changes in the different kinds of electrical cable used, the open junction boxes in the basement and attic, and the mess that is my electrical system. The photo below shows at least three different kinds of cable entering this junction box.

An electrician who looked at my house early on told me the whole thing needed to be rewired. Yikes! That sounds expensive . . . because it is! So, my plan is to redo the basement wiring when I remodel. I’ll do what I can with the rest later.

My first step has been to figure out which breakers control which loads.

Electrical safety

Messing with the 110 or 220 volt electricity in your house can be dangerous. You shouldn’t need to open any junction boxes or take the cover off the electrical panel just to map out your circuits. But if for some reason you do find yourself face-to-face with bare copper, don’t trust the breaker. It’s a good practice always to test and make sure the electricity really is off before you start touching the conductors.

These days, you can find many different devices that can tell you whether your wiring is hot (energized). The photo above shows the simplest type and is one I got from my grandfather. It’s just two leads you use touch to the wires. If the tip lights up, as it is in the photo, the wires are hot. Always test. And then test again to be sure. Above all, call a pro when you need to.

Step-by-step process

Last summer I spent a whole weekend mapping out all of the circuits in my house. I did it myself and made a whole lot of steps going from the electrical panel to every part of the house, flipping breakers and switches.

So, where should you start if you want to do this in your house? That’s easy. First look at the panel to assess what you’re starting with. If it’s labeled, you may have a head start. But don’t automatically trust what’s written there. Use the labels only as a guide.

Second, identify the two kinds of breakers in the panel. Some are big double breakers, two separate breakers that switch—and trip—together. Others are single breakers, usually 15 or 20 amps. In the photo of my panel below, there are four double breakers. On the top left is a double 15 amp breaker (two 15 amp breakers ). Right below that is a single 20 amp breaker, then a double 40 amp breaker. The left-side breakers, top to bottom, are for a Mitsubishi ductless heat pump in the sunroom, the now-removed whole-house fan replaced by my attic exhaust fan, and the larger Mitsubishi heat pump that heats and cools most of the main floor.

On the right side is a double 30 amp breaker at the top, another double 30 amp breaker in the middle, and then a single 20 amp breaker at the bottom. They protect the heat pump water heater, the electric cooktop in the basement, and lights and outlets on the back side of the house.

When you start mapping out the circuits, begin with the big, double breakers. They are the ones most likely to be labeled correctly to begin with. The big ones usually protect:

• Air conditioners or heat pumps
• Water heater
• Range and oven
• Clothes dryer
• Electric vehicle charger

There could be other big loads, and you may not have all of the ones above. If you use gas for heating water, cooking, and drying clothes, you won’t have double breakers for those.

The harder ones to map out are the many small electrical loads: lights, outlets, fans, dishwasher, built-in radio (above), garbage disposal, and anything else hard-wired into the house.

Matching loads to breakers

The easy version of the old-fashioned way to do it would be to have two people talking to each other from different parts of the house. One will stay at the panel, turning breakers on and off. The other person will go to each room in the house as well as looking at exterior lights as the panel person switches breakers.

If you’re doing it alone, you can save some steps when testing outlets by plugging in a radio turned up loud enough to hear at the panel. (Hat tip to Jeffrey Chalmers of Ontario for posting that idea on LinkedIn.) For lights and other loads, you’re going to get a lot of steps doing it the old-fashioned way by yourself.

If that’s old-fashioned, you ask, then what’s the new-fashioned way? There are tools available now that can help. The Klein Tools ET310 is one that I tried on my house. Unfortunately, I kept getting false positives. The receiver would light up indicating I had the right breaker, but then it would light up on another breaker as well. But the transmitter (plug-in part) is useful for other things, too, like confirming that a lot of my outlets aren’t grounded. Other people I know have had good luck with these kinds of tools, though, so it may be worth a try.

Another tool that can help is the Emporia Vue whole-house electricity monitor. You can turn loads on or off in the circuits you’ve set up for monitoring and see if they affect the result. It helped me identify a mystery load, which turned out to be the cooktop in our basement.

Whichever way you map the circuits, it’s essential to keep good notes and make sure you’ve got the correct breaker number written down for each electrical load. And then go back and check everything again. The bigger the house and the more complicated the electrical system, the longer it will take to get the electrical circuits all mapped out.

Organizing the results

Once you’ve got everything mapped out, your life will be easier. But don’t stop yet. Organize the data you’ve collected. First, of course, you want a numerical list of the circuits and what each breaker controls. That’s the norm, but most panels don’t give you space to list every load on each circuit. This is especially true for older houses. My busiest circuit, for example, has a dozen different loads in the basement, the main floor, the attic, and even one outdoor light.

I entered all my circuit information into a spreadsheet on three different tabs. The first tab is the by-circuit information I just described. It’s got four columns: circuit number, level of the house, room, and description of the load. You can see a screenshot of the top of it below.

The second tab is the by-load data. This one makes it easy to find the breaker number for any load in any room of the house. It’s actually more useful than the first tab because we usually start with a particular load we need to shut off. Again, I’ve organized my list with the same four categories as the first tab. They’re just in a different order.

The third tab (not shown here) is basically the same info and organization as the first tab, but I’ve put it into two side-by-side sets to match what I see in the panel.

You can take this even further, too. Jonathan Porter, an engineer in Minnesota, made a full schematic design of every circuit in his house. It shows every load, cable, junction box, and breaker. Joe Smith, a contractor in California, labeled not only his breakers in the panel but also the switches and receptacles in the house. Dennis Heidner, an engineer in Seattle, drew a schematic layout of his system and labeled the cables, too. How OCD will you be with your circuit mapping?

A step in the electrification process

If you, like me and many others, are going all-electric, mapping out your circuits is an essential task. In my case, it has helped future work I’ll be doing. My panel currently has a breaker in every available slot. To add circuits, I’d need to get a bigger panel or a sub-panel.

Or I could find circuits I don’t need anymore, and that’s exactly what my circuit mapping efforts helped me with. For example, we have a kitchenette in the basement with an electric cooktop. That uses two slots in the panel for a double 30 amp breaker. We also have a big whirlpool tub we’ll probably ditch and a few circuits with almost no load that we can combine.

In the end, labeling the panel and measuring your electrical use with something like the Emporia Vue makes the electrification process easier in many ways. Have you mapped your circuits yet?

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Allison A. Bailes III, PhD is a speaker, writer, building science consultant, and the founder of Energy Vanguard in Decatur, Georgia. He has a doctorate in physics and is the author of a popular book on building science. He also writes the Energy Vanguard Blog. You can follow him on Twitter at @EnergyVanguard. Photos courtesy of author.