> how I might fix the circuit breaker in my house.
Don't be so disappointed, here's my tip for you. In electrical installations, every subcircuit should have its own RCD/GFCI circuit breakers installed, rather than relying a RCI/GFCI breaker on the higher hierarchy. Otherwise the circuit breakers are misconfigurated - failing to do so would make troubleshooting leakage current (read "tripping breakers") extremely difficult.
But when it happens, there's a solution. I once fixed one at my home that always trips spontaneously, the secret is using a leakage current clamp meter. A RCD/GFCI circuit breaker trips when the leakage current is greater than its threshold to protect equipment and people. With a leakage clamp meter, it allows you to monitor the leakage current in real-time rather than hopelessly trying in the dark. You just clamp the meter across BOTH the live and neutral wire on the main breaker (if both wires carry the same current in the opposite directions, i.e. no leakage, net magnetic flux inside the sensor will be zero, so the meter reads 0 mA, and vice versa), turn off every subcircuit, and starts switching on different subcircuits one-by-one. If you see the leakage current substantially increases after you switched on a specific subcircuit, repeat the process by disconnecting all appliances from that subcircuit and connecting them one-by-one while observing the meter. Finally you'll find the smoking gun (if there's still significant leakage when nothing is connected, it means the wiring is at fault), mine was a light fixture with damaged insulation.
A leakage current clamp costs $200-$300, Fluke's meter will cost you $600. However, you can get a good enough, low-accuracy leakage clamp from China on AliExpress for $50-$100, just make sure the product description mentions "leakage" (the laws of physics are the same for all current clamp meters, but most are not designed to sense sub-10 mA leakage current).
In my experience, only a handful of electricians working with home wirings are aware of this diagnostic technique. I learned it from an application note of an industrial system.
