Why would one leg of my main breaker be running hotter than the other?

The short answer is that a thermal reading without an actual temperature scale or an amp load measurement is basically useless. Thermal cameras automatically adjust thier color palette based on the hottest and coldest points in the frame. If one leg is 85 degrees and the other is 80, the camera will make the 85-degree wire look like it's glowing red hot even though both are well within safe operating limits. Wires generate heat whenever current flows thru them, so seeing some warmth is completly normal, especially if you had the AC or other heavy appliances running. An unbalanced load is the most likely culprit if the heat is legitimate. Most houses have 120V circuits distributed across two phases. If your AC, hair dryers, or kitchen appliances are mostly pulling from one side of the bus bar during the inspection, that main feeder will naturally be warmer than the other. It doesn't mean anything is broken; it just means that leg is doing more work at that specific moment. Unless the inspector can show that the wire is exceeding its temperature rating—usally 60°C or 75°C depending on the insulation type—there isn't acutally a deficiency to report. If you want to get ahead of the buyers, have an electrician come out to do a quick **load calculation** and check the torque on the lugs. Sometimes a set screw can vibrate loose over twenty years, creating a high-resistance connection that generates excess heat. A simple turn of a torque wrench can often solve the problem in five minutes. If the connections are tight and the amp draw is roughly balanced across the phases, then the inspector was just blowing smoke without providing the data to back it up. Don't let them scare you into a panel replacement or a massive credit yet. Ask for the specific temperature readings from the report. If they can't provide a number, they're just guessing based on a pretty colors. A **clamp-on ammeter** reading is the only way to know if that heat is proportional to the load or if you actually have a high-resistance connection that needs attention.

Seen this a hundred times. These greenhorn inspectors love their fancy thermal gadgets but don't know how to use 'em. Back in the day, we'd just use a clamp-on or even a quick touch of the back of the hand—if you're brave—to see if somethig was actually cooking. If your AC is a 240v unit, it shouldn't be skewing one leg that much anyway unless the internal windings are going. Most likely, you've got a bunch of 120v kitchen loads on one side. I'd pull the dead front and check for any discoloration on the insulation. If the copper ain't turning colors and the lug is tight, tell 'em to pound sand.

Wow, I'm just starting to learn about how panels work and this is so cool to read about! I had no idea the cameras coud be that misleading just based on the color settings. Since everyone is talking about load balancing, it makes me wonder—if you have a ton of smart home gadgets and LED strips plugged into one side of the house, does that tiny 'phantom' power draw acutally add up enought to show up on a thermal scan? Or is it realy only the big stuff like the AC that matters for those readings?

Check the lugs for signs of 'cold flow' or oxidation, especally if you’re running aluminum feeders. If it’s an older Square D QO or a Homeline, those main breaker connections need to be hit with a torque wrench to about 45-50 lb-in depending on the wire gauge. Also, take a look at the neutral. If you have a loose neutral at the weatherhead or the meter base, it can force current back thru paths it shouldn't, causing one leg to cook while the other stays cool. I’d grab a Fluke 323 and check the amperage on both legs while the AC is cranking. If the delta is more than 20%, you might just need to move a few 15A breakers around.

Quick update — I had an electrician come out today and you guys were spot on about the thermal camera being misleading. He used a clamp-on meter and found the load was just slightly unbalanced becasue of the window units. He torqued down the lugs just to be safe, but there was no actual damage or overheating. What a relief!