mains wiring tester

40 A. Scragg mains wiring tester Here we have yet snother simple cir- cuit, consisting of two neon lamps (with built in series resistors) a push- button and an optional 100 k re- sistor. Can this circuit really be con- sidered as a piece of "test equip- ment"? Of course it can. In fact simpte ideas are the ones that are push to test used over and over again until they become indispensable. Consider how simple a phase tester is! However, those devices can on!y show whether the "live" mains connection is good or not, which leaves the user guessing about the negative and earth lines .. . But not any more! The mains wiring tester shown here will enable all three lines to be checked by simply pressing a button. When the circuit is connected to the mains both neons will light dimly. If the push button is now pressed one lamp will go out completely and the other will light properly. This in fact tells us three things: there is a phase present, the "live" line is the one with the lit neon...