I am starting this page with ideas of some homemade electrical testers for special troubleshooting purposes. I’ll let one of you guys patent and market these.
Power-restored buzzer. To know if power has returned to dead outlets in one room when you are testing outlets or purposely disturbing connections in another, I have found a 120-volt buzzer out of an older smoke alarm can be heard across much of a house. Rig it to a short cord-and-plug and plug it in.
Short-gone buzzer. As you disturb or disconnect one thing after another to narrow down where a short is happening on a tripped circuit, it is a nuisance to have to keep doing a resistance check or to keep retrying the breaker. So I rigged a 9-volt-powered buzzer that alarms when its two leads lose continuity to each other (through the shorted wires you attach them to). It uses a little relay. Of course, if you are after a line-to-neutral short, it won’t alarm when it should if there are loads (below a certain resistance) still connected on that part of the circuit.
Power-lost buzzer. This is for an intermittent open that is not now open. As you disturb connections here and there, it will let you know immediately (from the next room) that power is gone again. It uses a cord-and-plug and a different relay.
Tripped-GFI indicator. This is for an open-hot standard receptacle when you wonder if it is dead from a tripped GFI receptacle upstream. People do sometimes protect strings of outlets that aren’t required to be protected. For this, I rigged a very short cord-and-plug out the back of a single-AA flashlight, with the ground and neutral wires making continuity through the flashlight bulb and battery (I cut off the prong for the hot). It’s just a special continuity tester to see if there is continuity between ground and neutral (back at the panel), which would normally be the case. Most GFI receptacles (though not most GFI breakers) disconnect the neutral as well as the hot. Of course the test won’t be conclusive, because it depends on a good ground and because there are other conditions that can make both hot and neutral discontinuous from their sources.
Fancy outlet tester. I still use 3-prong testers for outlets, but I have encountered enough strange readings that I have designed a more sophisticated model. It uses power brought by an extension cord from a good outlet to positively tell me whether each of the three receivers of the outlet I am testing is hot, grounded, or just plain dead (open). It uses seven neon lights.
If there are other troubleshooting topics you’d like to see addressed here, let me know. I’m not interested in starting a forum, but we could provide a little something for tradespeople here. If you call or email me identifying yourself as an electrician, I will waive any charges, unless you are wanting to pick my brain for a problem you are working on. See How to Contact Detective Larry.