AC (+) and (-) finder circuit


Joined Dec 20, 2007
Hi Eplanet,
Mains power is Alternating Current. It does not have + and - because its polarity keeps alternating. Direct Current (like from a battery) has + and -.


Joined Apr 20, 2004
In a modern system with a ground wire run separately, a voltmeter can find the AC hot, as it will be the one wire that is: Inside black or red insulation, and is the only wire to show line voltage to both AC common and ground.

Thread Starter


Joined Oct 25, 2007
i see somewhere that not exist any standard colors for wire but i use standard ways and occurs very bad event i don't want to use DMM. i need very simple circuit.
i know there is no + and - for AC i mean phase and ground. i need electronic circuit for indicating phase and ground for exp with LED or buzzer. this is tool for repairing electrical device.



Joined Jan 11, 2009
connect a ne22 neon tube ( think that is the number ) with a high reisitance 5 meg ( series ). ground one end, the tub will light when the other end is connected to the hot wire. you may need to run ohm's law to get the value of the resistor right. these testers come all made up, buy one? ( the neon tube is a very low current device ) for higher current use a lamp in a socket with pig tails, also a very standard item.


Joined Apr 20, 2004
As long as everything is insulated, that will find the AC line. The "usual" resistor for a NE2 is 270K - 470K. 2M will be very dim.