When we moved to a new house I noticed a strangely wired up outlet:

Outlet Wirings - Spliced white wire goes to provide electricity to the boiler

For this outlet, I am really suspicious whether the grounding is messed up and mixed up with the Neutral.

Normally Neutral and the Live wires are the thicker ones right? If that is the case this outlet is violating that and the whole houses ground connections will have leaking voltage right? When I measured some of the grounded equipment I saw the line's tester's light is turning on and saw some nonzero voltages(for example my PC case).

Apparently to save one outlet somebody directly used that outlet and extended a wire into the balcony which feeds the central heating boiler of the house. If the wiring is wrong how is the breaker not tripping? Isn't this extremely dangerous the boiler sending its current back from the ground path?

-- To be sure, how do I find out if I have a Neutral-Ground mix-up fault?

On a side note, will this bother other electronics? For example I have a long 10M HDMI cable monitor. This monitor loses sync everytime someone turns ON an on-wall lamp switch at our home. ( Loses sync and blanks for a few seconds and turns back on after ). Can this probable fault be a reason why this is happening? For reference the German standard for electrical wiring (my country uses the same Page 14-15 of : [this IEC related document] 2 ): German Standard Example home wiring

  • 1
    you may be in a country that does not use a neutral ... an electrician from your country is very likely to read your question on the home improvement site
    – jsotola
    May 16, 2022 at 18:02
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    if the neutral and ground are bonded at the breaker panel, then that is exactly what a continuity buzzer will do
    – jsotola
    May 16, 2022 at 18:10
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    @KoolBreeze Your link is to a description of US wiring. OP's installation is not using US wiring colours so isn't there.
    – Graham Nye
    May 16, 2022 at 18:57
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    Neutral and ground are to connected together only at the main panel, nowhere else, not at outlets, switches, lights or sub panels. I think Europe changed their colour scheme years ago, so you will need to see the old colours to see if black was used as neutral or ground, think bare or green with/out colour is the only colour for ground everywhere.
    – crip659
    May 16, 2022 at 19:00
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    @NerdyNerdie You need to tell us which country this installation is in if you want help. Whilst the boiler cable uses modern IEC colours the fixed wiring doesn't use either new or old German wiring colours.
    – Graham Nye
    May 16, 2022 at 19:03

4 Answers 4


Neutral is not Earth

They are completely different wires with completely different jobs. Neutral is the normal everyday path for return current. Earth is a fault catcher, it only flows current when a fault of some kind is happening (and stops as soon as current trips the circuit breaker or RCD/GFCI).

Putting active daily current on earth is out of the question.

I see you using 'GND' to describe "Ground" as you call it, which tells me you've cut your teeth in small electronics. That is a completely different world. In electronics there is no proper earthing, and "GND" is simply the negative/Vss/backplane/common that is wired to everything as the common return loop... which would make it more like AC mains "neutral".

I gather you're from the Euro-system of wiring, which means, you call that thing EARTH. That is a relief: over in North America we call it "Ground" which makes it much harder to RE-train electronics folks. So keep calling it EARTH, or at least as "safety ground" as a different thing from GND.

I never call it GND, and I'm a Yankee.

Also unlike electronics, neutral is not "common" either. In AC mains we are running the wires at hard ampacity limits all the time, which means, each live supply wire MUST have a dedicated neutral wire that returns only its current. We can't be careless and treat neutral like a common/backplane, because then, 1 neutral might end up returning current for 2-3 live wires, and it would be overloaded! Neutrals don't have circuit breakers - they don't need breakers if wired correctly. (even on an RCBO, the neutral goes through the RCBO for RCD sensing, but does not have its own overcurrent detector).

Earths are yellow/green

Or straight green, or bare. This is a world standard and is largely effective outside the old Soviet bloc. Even the Yankees agree on it!

Very much unlike neutral, all earth wires should be tied together in all locations. Since earth doesn't carry current except during fault conditions, we don't need to worry so much about thermal overloads from continuously carrying high current. Service current is never on earth.

Find out about local legacy neutral and earth colors

I've never heard of a country where they used the same color for both neutral and earth at the same time. However there have been changes.

  • Modern Euro/3-continent standard: Light blue for neutral, brown for live
  • Au, NZ and old UK standard: Black for neutral, red for live
  • Americas standard: White for neutral, black for live

So you will need to ask local experts for the old wire colors, and see if that explains what you see.

Prepare for the possibility that your old work was done before earthing became a standard, and there may be no earth at all. Also, some locations used metal conduit for wires, and in that case the metal conduit is typically a valid earth!

Test the neutral by isolating it

Neutral has an equipotential bond with earth, either at the panel/consumer unit or on the power company side of it. This is to keep voltages at a reasonable voltage and to suppress transformer leaks, lightning etc. It also gives a current path for fault current to complete its circuit. Do not treat this as a license to treat them as equal or to tie them together elsewhere!

Once you know which circuit you are dealing with, and can identify the circuit breaker that turns it off... if you are qualified to do so, you can go into the breaker panel (consumer unit). From the circuit breaker you can identify the circuit's live wire, and then identify the circuit's neutral. With the breaker off, you can disconnect the neutral from the breaker or neutral bar.

Now there should be no connection between neutral and earth. With the circuit breaker off, live+neutral (together) should be isolated from earth.

You can also try energizing the circuit with neutral disconnected. In that case, on a properly isolated circuit,

  • neutral will be isolated if all loads are off (a DVM will show a phantom voltage of a fraction of normal voltage).
  • if any loads are turned on, neutral will snap to line voltage (e.g. 230V) in all locations. That is one reason the neutral wire is insulated.
  • All loads should be inoperative. If you find a load that is working, it is bootlegging neutral from earth.

If you find yourself with an earth wire which is not plainly marked (e.g. it is the wrong color, or the former earth color is now a neutral color etc.), then wrap it with green or yellow/green electrical tape at the least. That is not authorized by the electrical code, but it will make it clear what it's being used for. Identify the wire carefully and always mark both ends of a wire the same, at the same time.

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    Harper would you agree with suggesting that this poster switch the two black wires "and see what happens"? Surely the heavier black wire is meant to be current carrying in normal operation the thicker one should be on the neutral contact. May 18, 2022 at 0:55
  • Do the two black wires and the accompanying blue go to another receptacle? Are the three wires on lower right coming from the panel (consumer unit)? Does the "boiler" plug into this receptacle? Perhaps the three wires going to upper left should all be reconnected: blue for neutral, heavier black for hot and smaller black for earth. Then makesure the next receptacle is wired consistently. May 18, 2022 at 1:10
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    @JimStewart I prefer to isolate wires and test them individually and definitively. There aren't shortcuts. May 18, 2022 at 1:18
  • Also, German domestic wiring is three-phase, and although brown is the commonest colour for "live", black and grey are also "live". Oct 24, 2022 at 12:45

An RCD in circuit should have tripped, had neutral and ground got swapped in the outlet in question.

Here's a way to check for the swap.

  1. Switch off the main incoming 2-pole circuit breaker. That would isolate the line and neutral from the house wiring.

  2. Check for continuity between the neutral point of that outlet and earth point of another.

  3. Then check for continuity between the earth point of that outlet and the neutral point of another.

A positive result in the above two checks would confirm the swap.

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    So in Europe with single phase 240 V power, the main incoming circuit breaker is 2-pole, i.e., it disconnects both the neutral and the hot from the incoming power lines? Are the neutral and the earth bonded together in the consumer unit or near to it? On which side of the main breaker are the neutral and earth bonded? May 18, 2022 at 0:07
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    @Jim Stewart - Yes, Jim, in Europe, with single phase 240 V power, the main incoming 2-pole circuit breaker disconnects both the line and the neutral. The neutral and earth are not bonded at the consumer unit.
    – vu2nan
    May 18, 2022 at 6:45
  • I have two breakers. One inside my house and the other one at the apartment entrance (kWh counter for electricity bills). Is the latter (external one) definitely the "main incoming 2-pole circuit breaker" you described? Can I confirm it is really "2-pole" by looking at it and finding part numbers/etc. ? May 24, 2022 at 11:14
  • Hi NerdyNerdie, A 2-pole circuit breaker will have 2 incoming and 2 outgoing wires.
    – vu2nan
    May 24, 2022 at 11:55
  • IMPORTANT: The OP appears to be in Germany. Domestic wiring in Germany is not "single phase 240V", it is three phase. Oct 24, 2022 at 12:47

Blue = hot, Black = neutral

Appears it was used in Czechoslovakia (mid 1970's for unearthed fixed wiring) and never used anywhere else on the globe.

This standard seems to be messy. The contemporaneous standard for earthed fixed wiring included both:

Blue = hot, Brown = neutral, Black = earth

Black = hot, Blue = neutral, Green/Yellow = earth

There is no easy way to diagnose a swapped neutral and earth.

  • Plug in detectors are unable to detect neutral-earth swap.
  • Earth and neutral should be bonded on the house side of the disconnect switch. So opening this switch will not help to resolve a fault)

Two relatively non-intrusive tests:

  • If there is a RCB, RCBO, ELD on this circuit and it is not tripping then the wiring is ok. These detect either the balance between currents into hot and out of neutral, or the presence of a current on the earth.
  • If a clip on current meter is available then it may be possible at the switchboard to compare current in hot with current in neutral.

Other tests involve disconnecting wires at the switchboard and should be done by an electrician.



As per comments, this tester does NOT show ground/neutral issues. Leaving for future readers.

There are a bunch of devices available for testing a 3 pin power socket.

Often called receptacle/socket tester or less nice "idiot box/tester" they're a simple plug-in unit that shows if all three wires are correct from the front. There's no more risk from using these than from plugging in a cable, compared to pushing probes into places hence the "idiot" term.

Example unit, though they come in many designs, they all have 3 neons and a chart to decode the lights. Mine's round.

enter image description here US sockets enter image description here

You'd need to test every wall-plate at a minimum, and every socket on every wall plate would be wise. Fortunately a test is super quick.

The "idiot" name is imprecise - these are cheap, easy to use and interpret, and form a useful quick tool in the electrician/handiperson's toolbox.

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    Is there a Euro wiring equivalent? May 17, 2022 at 1:57
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    The picture is definitely for US (clearly NEMA 5-15 plug). I know UK is different, not sure how much different. A quick search on Amazon UK finds a lot of definite junk, quite a bit of US stuff and some maybes. For example, amazon.co.uk/Labgear-Socket-Tester-Electrical-Neutral/dp/… looks like it may be actually safe and functional. But someone who knows UK stuff could probably confirm/deny. May 17, 2022 at 4:16
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    @manassehkatz-Moving2Codidact screwfix.com/p/kewtech-kewcheck-103-13a-socket-tester-230v-ac/… is another candidate. Screwfix has physical stores, so more likely their products are properly licensed
    – Tim
    May 17, 2022 at 9:18
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    But the question is whether or not the neutral and ground are mixed up, and these socket testers are completely useless for that purpose, right? If the ground and neutral are mixed up, then these will say that the wiring is correct, even though it's not. May 17, 2022 at 12:52
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    Agree with @TannerSwett - this tool will identify many types of incorrect wiring, but getting a reading of "correct" does not actually rule out certain types of bad wiring. You'll note the tool doesn't have a readout for "GRD/NEU REV", since it can't tell. If one suspects a ground/neutral swap, this tool won't help at all to confirm or refute that, and could actually mislead you into thinking the wiring is correct, since that's what the readout will say either way. May 17, 2022 at 13:42

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