Neutral and live wires in lighting fixture.

Discussion in 'Electricians' Talk' started by Aurelija, Mar 13, 2019.

  1. Aurelija

    Aurelija New Member

    Hey. So I have this light fixture that I needed to shorten the cable. There's only two wires and upon inspection before cutting they both seemed to be the same so I was hoping that once I strip it from the main casing one of them would be ribbed indicating it as neutral. However that's not the case. After striping both wires a bit more noticed that one of them has a white strand of thread inside. That is the only difference that I can see. Anyone seen anything like this and maybe someone could help. Which wire is witch? Sorry I am a bit of a novice at these things. Any help appreciated.
     
  2. chippie244

    chippie244 Well-Known Member

    You need to do a continuity test to see which goes where.
    Is it bayonet or edison screw?
     
  3. Aurelija

    Aurelija New Member

    It is edison screw.
     
  4. chippie244

    chippie244 Well-Known Member

    Pretty sure that live goes to the centre.
     
  5. Rulland

    Rulland Well-Known Member

    Agreed.
    Use a continuity check to confirm which one does.
     
  6. spinlondon

    spinlondon Well-Known Member

    As far as I’m aware it’s only certain Edison lamp sizes that require line to centre terminal.
    E14 and E27 for instance do not.
     
  7. Pollowick

    Pollowick Well-Known Member

    Have seen those with bare metal touchable with lamps screwed in.

    And what if someone changes a lamp with power still on - say on a circuit with multiple switches? Even if they do not touch the fitting, they may well touch the cap sides which will be live.
     
  8. Comlec

    Comlec Well-Known Member

    This is what @spinlondon is referring to

    643.6
    Polarity
    Where relevant, the polarity of the supply at the origin of the installation shall be verified before the installation is energized. Where single-pole switching devices are not permitted in the neutral conductor, a test shall be made to verify that all such devices are connected in the line conductor(s) only.
    During the polarity test, it shall be verified that:
    (i) every fuse and single-pole control and protective device is connected in the line conductor only, and
    (ii) except for E14 and E27 lampholders to BS EN 60238, in circuits having an earthed neutral conductor, centre contact bayonet and Edison screw lampholders have the outer or screwed contacts connected to the neutral conductor, and
    (iii) wiring has been correctly connected throughout the installation.
     
  9. chippie244

    chippie244 Well-Known Member

    Would the OP be able to work out if the lampholder was to BS EN 60238 and the circuit had an earthed neutral condutor or not?
     
  10. Pollowick

    Pollowick Well-Known Member

    And it is unlikely that the specific circuit has an earthed neutral conductor. The supply may be, but does the circuit?
     
  11. Risteard

    Risteard Well-Known Member

    Of course it would. If the conductor wasn't tied to earth then it wouldn't be a neutral conductor.
     
  12. Pollowick

    Pollowick Well-Known Member

    So, you earth the neutral on every circuit?
     
  13. spinlondon

    spinlondon Well-Known Member

    559.5.1.206 In circuits of a TN or TT system, except for E14 and E27 lampholders complying with BS EN 60238, the outer contact of every Edison screw or single centre bayonet cap type lampholder shall be connected to the neutral conductor. This regulation also applies to track mounted systems.
     
  14. MGW

    MGW Well-Known Member

    Never thought about it before, but a reduced low voltage system is a TN or TT as the centre tap is earthed but it does not have a neutral supply only line 1, line 2, and some times earth, so neither contact is connected to neutral. I have looked for what BS EN 60238 means but can't find a 100% answer, however it would seem there is a shield that the bulb screws into so the outer can't be touched once fitted and it does not connect to the screw thread until fully screwed home.

    I have worked with them, real pain when glass breaks getting them out with pointed noise pliers. I sat there before Christmas was a junior hack saw shorting the outers on the SES holders so they would take LED bulbs. So think you can't use BS EN 60238 with LED? the LED base is too large.

    It does seem many people don't know what a neutral is!
     
  15. chippie244

    chippie244 Well-Known Member

    Are these posts helpful for the OP who obviously isn't a sparks to find out where to connect his wires?

    I can see that in certain cases the live can go to the outer connector but would it matter in any circumstances if the live was wired to the centre pin?
     
  16. MGW

    MGW Well-Known Member

    Yes agreed, so how would you tell some one to find out which wire is centre pin? Other than some device be it a bell and battery, or a meter, with two clear cables no real way to find out.

    I got my first multi-meter at around 14 years old, an AVO Multiminor, second hand it was around two months pocket money. And then I burnt it out. Measured volts on the current range.

    I question telling people to buy multi-meters even if today they are cheap, other than the clamp on, it is so easy to select the wrong range. I wanted to do 'A' level maths, and if I did two other 'A' levels I could do it for £10 so also did Photography and Physics, in the Physics lesson 10 students were given multi-meters and tutored how to use them, six by end of lesson had blown fuses in them. And this with "Advanced" students!!!!

    We as electricians know how important inspection and testing is, however how can it be made safe for the DIY guy? [​IMG] Yes plug in testers, but you can still get it wrong, and that little lot costs £60, socket tester £8 to check polarity, light bulb tester around £70. So how would you tell a DIY man how to test in a safe way with tools of under £10?
     
  17. chippie244

    chippie244 Well-Known Member

    What I meant was regardless of what the circuit is or the ES number or the BS number would the OP be safe under all circumstances connecting live to the centre pin.
     
  18. MGW

    MGW Well-Known Member

    Yes live centre pin when ever possible.
     
  19. chippie244

    chippie244 Well-Known Member

    OP, you need to buy or borrow a cheap multimeter, one on sale on this site for £10 and then check which wire goes to the centre pin on your lamp holder.
    To check continuity insert the leads on the multimeter into the correct holes and turn the dial to the ohm scale, which is possibly at the bottom of the dial, and one of them will have a sounder sign or something similar, if you touch the two probes together either the scale will go to zero or it will buzz, that means you have continuity.
    Then check your wires.
     
  20. Risteard

    Risteard Well-Known Member

    The neutral is earthed at the source. That's why it's neutral. That's why it is 0V relative to earth.

    I didn't suggest that I physically connect them together to give a TN-C system - where did you get that ludicrous idea from?
     

Share This Page