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I have bought a house in Germany and there were some different color sockets in some rooms so we decided to change them.

I will now explain for just one socket not to confuse the matter further.

Switched off the electricity and tested (with electrical tester) that there is no electricity and then I replaced the socket nest.

In Germany the blue cable is supposed to be the Neutral and the black is supposed to be the Live/Hot wire. Double checked it just to be sure and installed the socket like this.

I decided to buy a Socket tester and test the socket anyway (I want to make sure all the sockets at home are without any faults) - I bought this one "Kaiweets HT106D socket tester pro".

When testing the tester showed "Live/Neutral Reverse".

This is weird. I connected the black cables(2) at L and the blue cables at N. And the tester says that the "Live/Neutral Reverse" is reversed.

I said okay, I will now reverse and connect the blue cables(2) to L and the black cables (2) to N (against the standard). And then the tester lights "Correct".

Here are some photos of the socket, installed with the wrong color wires on which the socket tester lights it is all correct:

The front of the socket, where is clear that the L is on left, N is on right and the ground in the middle: The front of the socket, where is clear that the L is on left, N is on right and the ground in the middle

The wiring after I reversed the cables and connected them against the logic (here they are visually wrongly connected) The wiring after I reversed the cables and connected them against the logic (here they are visually wrongly connected)

The tester lighting correct, where the cables are connected against the logic (blue in L and black in N).

The tester lighting correct, where the cables are connected against the logic (blue in L and black in N)

Can someone give me a an advice: should I believe the cable colours or the Socket tester lights?

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    It seems likely the installer did not follow the color code. But just to be sure, take your tester to a friend's house or commercial establishment, plug it in and confirm that it's giving the correct indication.
    – Mark Leavitt
    Apr 8 at 18:04
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    My first question is, since you are not an electrician, do you know that under the German law you are not even allowed to change mains sockets? There is a reason for that, it is called safety, and you are now liable for any mistakes, burnt houses and electrocuted kids. But otherwise, the wiring color and left neutral sounds familiar, but in practice it does not matter much, since you don't know which way the live and neutral are in the Schuko plug that gets inserted into Schuko socket anyway.
    – Justme
    Apr 8 at 19:10
  • How do you know what's right? Schuko plugs can always be inserted both ways. That's actually very bad (since very few devices have a power switch that switch both wires), but there's little you can do about that (except for using something else than Schuko sockets)
    – PMF
    Apr 8 at 19:33
  • In the U.S. we call those "Magic 8-ball testers" since their answers are so often whimsical, in terms of totally failing to describe the actual problem. Here's one with a more accurate label. Apr 8 at 21:07
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The socket you have there is called a "Schuko" (or CEE 7/3 and 7/4, to be formal).

This socket is entirely unpolarized, by nature. The socket design makes no differentiation between hot and neutral. The plug can simply be flipped over, and the two are exchanged.

Part of a genuine CE listing (or the third party tested TUV, BSI etc. ratings) is that every appliance must be designed to be safe with either conductor hot.

So the simple answer is that when you get "Hot-Neutral Reverse" on a tester, it means you plugged the tester in upside-down :) Really, we could do a whole comedy sketch here, because it's entirely a matter of perspective!

Meanwhile, in Canada... NEMA 6 sockets are polarized even though both working contacts are "hot" at 120V and there's no reason whatsoever to polarize them.

Also, you selected a cheap Chinese mail-order tester, we've seen the unit around here before under a different name. Like all that stuff, it is sold direct-mail, which bypasses the government safety apparatus that keeps equipment safe. It lacks TUV certification, and the CE is completely phony. Using counterfeit safety equipment defeats the purpose.

enter image description here

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  • The NEMA 6 recs are slotted the way they are so that the plug type is unique and compatible only with suitable devices (eg 6-15P into 6-20R but not 6-20P into 6-15R and not 5-15 into either. Allowing them to flip is unnecessary and calls for either more complicated pin geometry or a larger plug/ less spacing between pins. Arguably, simpler manufacturing while allowing lower material use given the desired 15A to 20A compatibility are reasons for unnecessarily polarized receptacles to exist.
    – K H
    Apr 9 at 7:07
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I bought 3 pieces of the same tester, and all of them were wrong because they expected neutral on the left and live on the right pin. Which is wrong. I assume it is so in china or some other countries.
So I had to fix those testers. I had to open them and swap wires for live and neutral.

It seems your wiring was ok before, and the problem is in the tester.

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    "You had one job, tester!"
    – Hearth
    Apr 8 at 19:25
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    Sounds like a cheap Chinese tester. Using safety equipment from dubious sources pretty much defeats the purpose of using safety equipment. Apr 8 at 21:10
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    @Harper-ReinstateMonica that tester actually works pretty well (after fixing those swapped wires). for home use, basic check of wall plugs. Apr 8 at 22:20
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The best way to check your plug polarity is to get some simple multimeter and measure the voltage between ground and receptacles sockets. Neutral should be close to zero. If it is blue wire, wiring is correct. Mixing the color of wires is rare mistake, electricians choose color automatically. Tester wrong is more probability.

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