As an electrician newbie I have a question..

Short question

My power plug is attached to the wall outlet and three wires are at the end of it.. the blue, the brown and the green/yellow oen.

How to determine which is the live, zero and ground wire WITHOUT depending on the colouring? I want to know this to always be able to check the wiring, if I don't trust it.

Also, I have these sub questions that follow from my situation:

  • Why does the test screwdriver lit up when connected to the apparant zero line?
  • How can I determine the live/zero line using a multimeter


My tools:

  • a test screw driver
  • a multimeter
  • the ANET A6 manual

In the manual it states that

  • brown is the live wire
  • blue is the zero wire
  • green/yellow is the ground wire

I know that in some countries this colour coding is the standard and can be trusted. I just want to be able to check it.

So, my first hypothesis would be.. if I put the test screw driver on the live (brown) wire, lay my thumb on the end, the internal bulb would glow. This did not happen. It did happen when I put it on the zero (blue) wire. So I am a bit confused by this.

My second trick was using the multimeter. Using the positive and negative probes to determine the polarity and therefore decide how the current was flowing. But there was no sign of polarity... duh.. because I was of course on AC, which is always Alternating.. hence no sign information from a multimeter. So, how CAN I use a multimeter to determine the live/zero line? Maybe measure the current from live/zero to ground? Is that a safe option?

PS: my first post on this forum.. so please correct me where needed

  • 2
    $\begingroup$ Wouldn't this be best asked at the EE.SE? $\endgroup$
    – 0scar
    Mar 11, 2019 at 7:50
  • $\begingroup$ @0scar I thought, since this has to do with the Anet A6 wiring that this could be a nice place for it. But you do have a good point, shall I move it to there? $\endgroup$
    – zwep
    Mar 11, 2019 at 8:00
  • 2
    $\begingroup$ Don't worry about moving, the community decides! :) $\endgroup$
    – 0scar
    Mar 11, 2019 at 8:19
  • $\begingroup$ @0scar - This question would be dead on arrival over on EE.SE. $\endgroup$ Mar 11, 2019 at 12:35

2 Answers 2


As it is alternating current, why are you interested to know which is which? (I'm referring to the blue and the brown wire, the green/yellow has an obvious purpose)

E.g. a CEE 7/4 plug can be flipped around in the CEE 7/3 socket. When you flip the plug (180°), the brown and the blue switch places, it is all depending on how the electrician in your home attached the brown and blue wires in the socket and depends on the socket and plug you use.

The only benefit would be that when you cut the power with a relay, you may want to have the power on the side of the relay, not the printer; but again, that does not matter when you flip the plug 180°. Note that some plugs inhibit rotation, so it also depends on the plug and socket you use and where you are located.

  • $\begingroup$ oh god.. of course.. I never realized that when you turn it 180° the lines switch... then a follow up noob question.. how does my power supply for my Anet A6 deal with this possibility for switching internally? And why is there a standard on the 'live' and the 'zero' line then..? $\endgroup$
    – zwep
    Mar 11, 2019 at 8:03
  • $\begingroup$ @zwep remember it is alternating (AC), so it does not matter. The rectifier diodes in the PSU will create a DC from this AC. No matter how you attach it. Hook it up and have fun with printing! $\endgroup$
    – 0scar
    Mar 11, 2019 at 8:24
  • $\begingroup$ Thanks, yeah I understand that :) I just read some introductory things about rectifier diodes and how they translate the AC to DC. This definitely helped in my understanding of my PSU! $\endgroup$
    – zwep
    Mar 11, 2019 at 8:37
  • $\begingroup$ It matters a lot . The return line (blue) is intended to be at or near ground. The brown line is hot, and is the source of current. If your wall plug is wired wrong, that's a dangerous situation. Next, nearly every power supply i'm aware of expects "hot" on the marked post. If you cross the wires, the internal electronics will most likely fry due to potential differences between Return and Ground(neutral). BTW, the AC voltage sine wave is on the Brown wire, oscillating about the (hopefully) 0V return wire. The AC current is out of phase with the voltage most of the time. $\endgroup$ Mar 11, 2019 at 18:06
  • 1
    $\begingroup$ @CarlWitthoft It depends on where you live, you are probably accustomed to UK plugs, in Germany and The Netherlands you can flip the plugs, so it does not matter. I believe French and Italian sockets have a pin, so plugs cannot be flipped. $\endgroup$
    – 0scar
    Mar 11, 2019 at 18:22

This picture shows the correct wiring for a British 13A mains plug:

UK 13-amp mains plug with wiring

The green/yellow wire must always be connected to the earth terminal (at the top of the plug). This is most important, and will prevent electrocution if something goes wrong.

The brown (live) wire should be connected to the fuse, and the blue wire to the remaining terminal. It is true that, since alternating current is being used, the device will likely work if the blue and brown wires are swapped, but it is better to stick with standard practices to avoid confusion.

I would not use a "test" screwdriver to determine which terminal is "live" in this instance, simply because it is unnecessary. The live terminal is always the one that the fuse is connected to. This is done for safety reasons since the device is automatically disconnected from the live side of the circuit if the fuse blows.

How to wire mains plugs is really beyond the scope of this stack. Watch appropriate YouTube videos if you want to make a competent job of it. The only advice that I will give is to always use a proper fuse of the correct rating for the device. Never use something like a paper-clip. Also, don't use the 13 Amp fuse that comes with the plug. The fuse is there to protect the cable, rather than the device. Most printers will draw less than 5 Amps, and will be supplied with a 5 Amp cable, so use a 5 Amp fuse.

Also, never work on a plug while it is connected to the power socket. This is most foolhardy, even if the socket appears to be switched off.


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