Otherwise known as "know the electrical wiring in your house."
A few days ago, I was working on the back patio, and needed to use my shop-vac. I plugged it into the outlet on the patio, hit the power switch, and stared dumbfounded as nothing happened. The outlet had worked just fine the previous weekend!!! My first thought was "Oh great, the motor's blown." My first step at diagnosis was to detach the motor assembly from the shop-vac and put it into blower mode. Nope, no joy, so it wasn't any sort of interlock switch or something.
Next, I tried the other plug on that same outlet, just in case one blew or failed, even though there was no visual sign of melting or damage. That didn't work either, so I grabbed my multimeter to check the receptacle. When neither plug showed power, I headed to the breaker panel. I couldn't find a single breaker tripped, and even tried tripping and resetting a few likely ones (I wasn't sure exactly what circuit that receptacle was on).
When that didn't work, my next thought was that it had to be a GFI tripped somewhere. After all, this is an outdoor circuit, with wet environment exposure, so by code it must be on a GFI-protected circuit. None of the GFI plugs that I knew about on the ground floor were tripped. At this point, I just plugged my shop-vac into an inside outlet and took care of business. I figured I'd troubleshoot the circuit later.
Fast forward to yesterday, and I decided I REALLY wanted to get this receptacle fixed. At this point, I was honestly thinking that I'd somehow broken/damaged the receptacle the last time I used it. Just to be sure, though, I went back through the basic troubleshooting steps. Using my multimeter, I checked that receptacle (dead), the receptacle on the inside wall right next to it (good), and every other receptacle in the two downstairs areas next to the rear wall (all good). Even though all those circuits were good, I double-checked all of the GFI plugs, even tripping and resetting them. Throughout all of this, that outside plug remained stubbornly dead.
Finally, I decide to pull the receptacle. Once I had it out, I checked for power directly on the lines, and there was none. I then pulled the inside receptacle, and noticed that the jacket on that wire was a different color than the outside wire. Up to this point, I'd been working on the assumption those two plugs were on the same circuit. With that bit of information, I finally had an epiphany.
I went to the front porch, and sure enough, the receptacle there was dead too. AHA!!! Obviously, the front porch and rear patio are on the same circuit. I connected my multimeter to the front porch, asked my wife to watch it, and then went into the garage to start resetting breakers. 5 minutes later, and I still had a dead plug.
At this point, I was very confused. Everything I'd done so far should have found the fault, and I was mentally preparing myself to admit failure and schedule an electrician. Fortunately, my subconscious threw me a lifeline, and I remembered there was one general electrical outlet in the basement. I headed downstairs and sure enough, it's a GFI plug, and the little red light was glowing. I reset the plug and et voila!!! We have power.
I get everything put back together and buttoned back up, and all is at least somewhat right with my world again.
The number lesson in all of this is, as best as you can, understand all of the electrical circuits in your house. Know what zones and plugs are controlled by what breakers in your breaker box. Further, know where all of your GFI plugs are located, and what other plugs are on that same circuit. If a GFI plug trips, it disables the ENTIRE circuit, even though the breaker's not tripped at the box. It can be a rude awakening when a tripped GFI plug two rooms over disables the plug you are trying to use.
The other lesson is, if you're going to try and troubleshoot your wiring, have the proper tools and respect. Without a multimeter or other electrical tester, I would have had no safe and easy way to check all of my plugs to determine which ones were hot and which weren't. It also helps to have at least a basic understanding of how circuits work. You don't have to be an electrical engineer, but you should know what breakers and fuses do, and how to diagnose a faulty circuit. You should generally know the difference between hot, neutral and ground wires, and how to properly test a circuit using your testing tool.
The best part of all this, besides having a functioning circuit again? There's a wonderful sense of accomplishment in successfully "fixing" something that was "broken". There's a gratification in knowing you didn't have to spend money on the electrician. And there's the sense of relief that you didn't get embarrassed when the electrician points to the little glowing red light 2 minutes into his visit, saying "There's your problem."
Oh, and now I need to have a conversation with the kids and remind them not to play with the push-buttons on the receptacles, even if that little glowing light is kinda cool.