DIY AC 3-Pin Socket Tester

Introduction: DIY AC 3-Pin Socket Tester

About: Electrical, electronics, IoT, programming and wireless stuff is what I love the most.

AC 3-Pin Socket Testers are very simple electrical circuit testing tools. Just plug-in the tester and turn on the switch of the socket, the LEDs will detect any probable simple faults that the circuit might have.

Materials Required:-

  1. A 10 A 3-pin socket - 1 piece.
  2. 47K, 1 or 2 W (preferably 2 W) resistors - 3 pieces.
  3. 1N4007 diode - 3 pieces.
  4. 5mm LEDs ( Red, Green & Blue) - 1 piece each colour.
  5. Insulated connecting wires (if required).
  6. Soldering iron.
  7. Solder.
  8. PVC box (optional) [ You can also drill holes into the socket and make everything inside it]

Step 1: Faults to Be Detected



ON OFF OFF Missing Earth

OFF ON ON Live-Earth Reversed

ON OFF ON Live-Neutral Reversed

OFF ON OFF Missing Neutral

OFF OFF OFF Missing Live/ Missing Neutral & Earth

Step 2: Schematic

Due to the high heat generated, a 2W resistor is preferred. If the LED glows dim, change the resistor value to a lower value or vice versa.

Step 3: PCB Designing

My PCB is designed using .

Make changes according to your needs.

Step 4: Developing PCB

Develop PCBs at

The PCBs will be provided if you need (contact for buying), but you can develop yours too.

You can omit PCB by directly soldering inside the socket, or use a veroboard.

Contact me on: Gmail:


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    3 months ago

    Getting ready to use this schematic - thanks for taking the time and sharing it. Actually I am using 2 of them for checking if it is safe to tie two AC circuits together to power a portable brazing unit. the other check is that both outlets are on the same leg of the breaker box, I'll just measure for 0v between the hots.


    Reply 3 months ago

    I am really glad that this is still inspiring some to come up with these amazing ideas. I think I should document some of my other projects too..and probably revisit this with better design soon, since I was just an undergrad student when I wrote this. But I really appreciate your kind words. It means a lot to me..

    By the way, that is an interesting application of yours. Have you thought about floating neutral condition? Properly regulated AC doesn't have issues with neutral, but I have seen some conditions where the return path did have some voltage mismatch, which creates problems when being connected together, though mostly happening in DC circuits. What do you think ?


    Reply 3 months ago

    So I'm assuming that using this circuit on both, then checking that they are on the same leg of the breaker box would get me pretty close. Once all three H,N, G are connected together, if at least one has a N, we would be good to go. But if your tester told me open N, then I wouldn't use that outlet anyway. I will have a 15A breaker on each, along with the 15a that is already on the outlet also. All tests must pass before I merge them. I am by no means an expert though, so I may possibly learn something new. I don't dare detail this project on any of the electrician sites though, they will all scream about fires and such. I work all day with electricity and gas, still alive! (for now) lol
    One question I had though, I can use momentary switches on your circuit if I need to, do you think they are OK to operate for a 1/2 hour or so?
    Also if one outlet has slightly less resistance to AC amps, could one outlet try to pass 20 amps and the other try to pass 5? I wonder. Of course that would hit the breaker(s), so we are protected, but this would render my project useless.


    10 months ago

    I noticed that the schematic and the PCB layout design is different.
    1. In the schematic the EARTH is connected R2 and R3 but in the PCB layout EARTH is connected to R1 and R2
    2. In the schematic the LIVE is connected R1 and D2 but in the PCB layout LIVE is connected to R3 and D2
    3. NEUTRAL is OK


    Question 10 months ago

    I'm just wondering if this can be made for use with a European socket as there seems to be no regulation for electricians to connect the live and neutral cables in the sockets when they install the sockets. Ie. The live and neutral maybe reversed. The live maybe on the left and neutral on the right...or vise versa. See picture attached.


    Answer 10 months ago

    Thank you Mr. Mark for your interest in my project. Firstly, I should be very honest about this, that I was just an engineering student when I wrote this, and I hadn't thought of every real life scenario that might arise. I might redo this project in my spare time, if people do think this is useful.
    Now, coming back to your question, electricians do connect live and neutral to any of the two pins, and as long as we have a voltage gradient between the two, our appliances do run perfectly fine, but still, it is good to have the live conductor on the right and the neutral on the left, which is how many of the appliances are designed with a fuse connected in series with the conductor that is supposed to go into the right socket-hole.
    But, in this given schematic, if the live is connected on the left conductor, (assuming we have a working ground/earth conductor too), the circuit will detect that there is a potential gradient between the earth and left conductor, but nearly no gradient between the earth and the right conductor. This establishes the fact that we do have the live and neutral wires in the wrong positions, and the LED indicators light up accordingly.

    Now, in your image, it looks like a 2-pin plug, so, there is no provision to check voltages using ground as the reference. Here, a quick and easy way to test if the live and neutral wires are wired the right way would be something like this....
    1. We take two paths from the two nodes : L-A-N and L-B-N
    2. Half-wave/Full-wave rectify A and B.
    3. Add a diode after rectification, one on each path, but in opposing direction.
    4. This would essentially mean, on one path, we get very high resistance, on another, very low.
    5. Now we can use a load+lamp assembly to detect which path has current flow, thus ascertaining the direction of Live and Neutral conductors.

    There are various other ways we can do the same thing, but the basic idea stays the same. But, I must say, I have no idea about the EU norms. If we do this in India, no one will say anything, but most certainly EU has the most stringent laws concerning electricity, so, I won't recommend anyone doing these, unless he/she is safe to do so by means of knowledge of electricity and local laws.


    Reply 4 years ago

    Thank You :-) Do share if you like, and comment about anything that you'd like me to make an instructable on.