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My home electrical system is single phase, two wire (live + neutral; grounding is short-circuited to the neutral). I have no schematics as to how it is connected. However, there is a separate circuit breaker for the lamps.

Today the ceiling lamp in the living room stopped working. The lamped is controlled by a two-way switch.

After conducting a series of experiments, I concluded that the neutral connection is faulty. Namely, a light bulb lights up when connected to the output of COM2/live input of my ceiling lamp and a reliable neutral, but stays dark when connected to the same output of COM2 and the ceiling lamp's neutral.

As can be seen from the schematic above, there is no junction box in between the lamp and the central electrical box (or I can not find one). Somehow, somewhere, there are more lights, connected parallel to this one, for the next room. Some of them stopped working too.

What should be done in this scenario? I would like to avoid bringing down my whole ceiling - maybe at least to know where to cut.

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2 Answers

It doesn't sound like you can yet definitively conclude that the neutral line is bad, however an easy way to verify a bad neutral connections would be to test continuity between neutral and ground at the light. You can do this even using a cheap voltimeter by setting it to a low resistance setting. More advanced voltimeters may have a special continuity check that will beep when it detects 0 resistance.

enter image description here

Since you have neutral and ground bars connected at your central box, you should show near 0 resistance between neutral and ground at the light. If it is 1 or a much higher number than you have infinite resistance meaning that your light is either not grounded properly, you have a disconnect somewhere on the ground wire, or you have a disconnect somewhere between the neutral wire and the neutral bar in your central box.

NOTE: You describe a two way switch, however this diagram shows what is called a three way switch in the United States. The load from the central box or from another receptacle on the circuit is either entering at one of the two switches or to the light itself. Identify which of these wires carry power and inspect the wire connections at the light for ground, neutral and hot at the switch boxes and at the light. Neutral's should be connected directly and not switched.

If these connections seem good then perform more continuity tests between ground and neutral at all locations to help identify if a wire is bad. More than likely the disconnect is a loose crimp or wire nut at one of these three locations.

If you still cannot find anything wrong at all three locations then the problem is likely at a receptacle or luminaire further down the circuit, as you mentioned that you are also experiencing problems with lights ahead of the circuit as well.

CAUTION: Many European single phase systems operate at a high voltage. As always be extremely careful and take your time when handling electricity!

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Hi, maple_shaft, nice to meet you here too (in yet another SE)! The diagram is correct, the "two-way switch" term came from google translate. I will edit my question accordingly, perform the suggested measurement, think about it, and post the results here. Have a nice day. –  Vorac Jan 7 '13 at 12:44
@Vorac Great, look forward to hearing back from you. Be careful! –  maple_shaft Jan 7 '13 at 12:56
"3-way" is used to describe this type of switch in the US, but it's often called a "two-way" in other countries. –  Tester101 Jan 7 '13 at 13:42
@Tester101 I wasn't aware of this naming difference, thank you. I added notes to point this out. –  maple_shaft Jan 7 '13 at 13:51
It is a two wire setup, there is no grounding. Probably you are right, that this a loose screw somewhere. Unfortunately I have no access to it whatsoever short of tearing the whole ceiling down :( –  Vorac Jan 11 '13 at 17:04
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[Caution: There is general agreement from the community that the below answer is dangerous and should not be attempted by anyone.]

I double checked that the neutral line is broken. Following that, I connected the lamp's neutral to an operational neutral nearby.

Unfortunately, the other lamp further down the chain is still not working. Not a big deal, but I wouldn't have minded if this was the root cause of everything.

The cable runs across the ceiling and then in the corners to the nearest power plug (incidentally also never used)

enter image description here

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There's so much wrong with what you've done here I can't begin to fathom it. –  The Evil Greebo Jan 11 '13 at 19:24
I think the only thing done correctly here, is that you've supported the wire at proper intervals. –  Tester101 Jan 11 '13 at 19:42
Crosswiring neutrals is a dangerous thing, and nobody should do this. –  maple_shaft Jan 11 '13 at 20:14
Could please someone explain what is the problem? I do not seem to be able co grasp it! Also, what should have I done? Honestly - please help! –  Vorac Jan 11 '13 at 20:20
@Vorac You can't (or shouldn't) borrow a neutral from another circuit. The wire should not be run separately from the other wires in the circuit. Exposed wiring should be protected from physical damage. All junctions should be in an enclosure (can't tell if this is done or not, but it looks like there is a taped up junction on the fixture wires). I'm fairly sure fixtures can't be supported by the fixture wires, but I'd have to look that up to be sure. For starters. –  Tester101 Jan 11 '13 at 20:51
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