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.
Best Answer
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.
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!