problem wiring a light

Discussion in 'General Electronics Chat' started by Col, Jun 25, 2012.

  1. Col

    Thread Starter Member

    Apr 19, 2012
    44
    2
    A problem... which in my mind is embarrassingly simple... but still has me scratching my head

    I'm wiring a simple ceiling light in the home... It's Finland so I have a screw block terminal and a hook on the ceiling, its pretty standard here. The terminal has 3 wires coming from the mains. black, red and grey. I read here that these are standard 3 phase colours (http://www.allaboutcircuits.com/vol_5/chpt_2/2.html) but I have also been told not to trust the wire colours in Finland. Also, 3 phase on a standard light fitting is surely not right. So to check I have used a phase test screwdriver to confirm red and black are 'hot', assume live and neutral, and gray is 'dead', presume ground.

    I continue to connect the blue and brown wires of the light fixture to the black and red. Respectively, although I believe there is no difference between live and neutral in respect of the light bulb. I leave the ground wire unconnected, pretty common for a ceiling light, right? With my phase test screwdriver I confirm that connection is made and connections to the bulb are 'hot'. However when I connect the bulb it does not work. I again check to see that the live & neutral are hot, but now they are not. Of course I have tried more than on bulb, and checked these bulbs in other lights. I also tried reversing the red and black, and as I expect no difference.

    Any idea what might cause this problem
     
  2. #12

    Expert

    Nov 30, 2010
    16,269
    6,781
    Ummm...you blew a fuse?

    Let's start with this: How is Finnish wiring done? Two phases of 120V bringing 240V to the socket and a neutral wire for the safety ground? That's how it would be done in USA if we had 240V light bulbs.

    Or you could have 2 energized wires of the same phase and that results in zero volts from black and red.

    This answer is based on the idea that I don't know jack about European wiring.
    We do have a guy from Finland, Nerdgutta. You might try to Personal Message him.
     
  3. Col

    Thread Starter Member

    Apr 19, 2012
    44
    2
    Ah sorry... I assumed... Yea its 220V only round these parts, we don't get 120V. 3 phase is 380 I believe but I really think that voltage has no business anywhere near a ceiling light

    No RCBs tripped or fuses blown.
     
  4. #12

    Expert

    Nov 30, 2010
    16,269
    6,781
    Can you measure from black to red and see if they have a voltage difference? I'm guessing you have red and black both hot compared to neutral, but both the same voltage and phase. You could try the bulb from red to neutral or black to neutral, but only one at a time. That might work as a test method.
     
    Last edited: Jun 25, 2012
  5. Col

    Thread Starter Member

    Apr 19, 2012
    44
    2
    Only have the phase test screwdriver with me today, which give a hot or not (light or not) for a single wire. Think it actually uses the person holding it as a reference, on reading up it sounds like a dangerous too actually... anyway thats a good idea, think i'll borrow a multimeter from work tomorrow and check it out
     
  6. #12

    Expert

    Nov 30, 2010
    16,269
    6,781
    That's better than "ignorant" trying to lead "can't measure"!
     
  7. Andrewedwardjudd

    New Member

    Oct 13, 2012
    1
    0
    In an older Finnish house the Grey is neutral.

    If the black and red were both live phases you would have created 400V and blown a 240V bulb.

    Often in Finland the main living room lamp will have a neutral and two live phases wired to a double switch to enable variable lighting of a multi bulb light so that one group of bulbs is connected to one phase and neutral and the other group to the other phase and neutral
     
    Last edited: Oct 13, 2012
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