I live in a 4 story apartment complex with a switch on every floor that goes to light all lamps in the stairway. I am located on the 3rd floor and a lot of cables pass by. I know that the brown cable goes all the way down to a relay and then comes back up with black colour. Unfortunately, there are two black cables and I don't know which goes where (4 different combinations). It tried one combination and the fuse popped and the other combination just ignites the light constantly (while there should be a 30s timer). More clumsy, I did not mark which combinations I tried.

Can I somehow identify which goes where?

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  • 1
    Apartment building means only a license electrician can do the work. Everybody else is limited to changing light bulbs.
    – crip659
    Jun 17, 2022 at 17:46

2 Answers 2


You're not allowed to work on electrical in a multi-apartment facility, certainly not one that has 4 floors. That's true all over the world, especially places that use brown-blue for power.

Your drawing is a case of "blind men and the elephant", you don't know what you're looking at and are taking a little visual information and a whole bunch of wild guessing. The drawing is "not even wrong".

I know you want to be "instantly red-pilled" on how this stuff works so you can change the circuit to your whim, but a) that's not allowed and b) wiring isn't simple like you want it to be. There are at least 2 ways this could be set up and neither one is simple. Nothing but a qualified expert will do.

And it's not your building to play with, and even the owner isn't allowed to DIY repairs, due to the fact that a fire or shock hazard will "inconvenience" a lot of innocent people potentially.

It tried one combination and the fuse popped and the other combination just ...

Yeah, this is the mark of sheer amateurism and says plain and clear that you need to put the tools down and call building management and ask them for what you want. The danger here isn't a combination "not working"... it's a combination working, and then killing people.

Because lots of combinations will work and then kill you. Or kill somebody, and then prison for you.

Not to be a downer or anything lol.


In most places, you can't do work on multi-tenant buildings unless you are a licensed electrician. Two of the reasons are:

  • Safety/Liability - Some things that might seem to work could put yourself, and other tenants, in danger.
  • Nuisance - A trained electrician will know how to do the work faster and therefore inconvenience all the other tenants for a much shorter period of time.

So you really can't do this yourself. Call the landlord (if it is a rental) or whoever is in charge of common area maintenance (if you own your apartment). Even if you happen to own the entire building, you still need a licensed electrician to do the work.

All that being said, a couple of things for the more general case (e.g., if this was in a single-family home):

  • A wire is a single copper or aluminum conductor inside installation. It is typically identified by color.
  • A cable contains multiple wires, generally each one a different color, inside a an outer wrapping.

In this case, it appears you have 4 wires, not cables. The terminology does matter.

  • Always take pictures before doing any work, unless there is exactly one way to connect things (e.g., only 2 wires). That way for a straight switch replacement, which I suspect is the situation here, you can connect the way the previous switch was connected.

In this specific situation, you may be dealing with a 3-way/4-way switch configuration. (US terminology - it may be different in your location.) With a 3-way/4-way switch configuration, the first switch (e.g., bottom floor) will have "1 in, 2 travelers", the last switch (e.g., top floor) will have "2 travelers, 1 out" and all the other switches (e.g., middle floors) will have "2 travelers in, 2 travelers out". I mention that because that looks sort of like your diagram - i.e., all black wires as travelers in/out of a 4-way switch. But then again, you have a red wire out to the light, which if it is real does not match but might just be conceptual.

If this were a single-family home, I would ask for pictures and a lot more details. But since it is not, hire an electrician.

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