The Use Of 1.0mm T + E In Domestic Lighting Circuits and 5 amp SO's

Discussion in 'Electricians' Talk' started by JP., Jan 24, 2018.

  1. JP.

    JP. Screwfix Select

    Guys I have always used 1.5mm for lighting circuits and always use the loop in box method. Looking back some of the lighting circuits I have placed in single and indeed double boxes sometimes crams conductors and can get messy. I just need forum inputs to start or not to start using 1mm generally, and so the question begs - How many of you are happy to use 1mm in lighting circuits? Breaker sizes and loading etc I have no problem with, and of course the cpc is the same size as 1.5 so no probs there or owt. Are you all happy with using 1mm largely in domestics? Would you be happy running 1mm for 5 amp so's or would you use 1.5mm in this scenario? I use 1.5mm myself at present. Security lighting I usually do as dedicated, and would not use 1mm for that type of thing. Any inputs greatly appreciated.
  2. Dr Bodgit

    Dr Bodgit Super Member

    Good question JP, I'm the same, use 1.5mm for lighting on 6 Amp MCB. I recently needed some 3&E are reckoned 1mm would be more than adequate as its carrying the load for just one light not the whole lot, and its a darn sight cheaper. But still prefer to use 1.5mm generally but I think the consensus is that 1mm is more than adequate. Lets see what the Sparks say :)
    Comlec likes this.
  3. Joe95

    Joe95 Screwfix Select

    Wiring here is a 1.5mm T&E 'backbone' (less concern about voltage drop and derating) and 1mm T&E to fittings.

    Price difference isn't a great deal, but 1mm is easier to work with. Particularly in the case of backboxes, as you said.
  4. Coloumb

    Coloumb Screwfix Select

    1mm is good for, what around 15a clipped direct and cost less p/m than 1.5. I've not ever used anything else tbh for lighting ctts. I would imagine the leccy goes down 1mm the cables in much the same way as it does 1.5mm so the difference imo is purely physiological.
  5. Peterdevon

    Peterdevon Active Member

    With most lighting being led these days, in a 3 bed house upstairs lights the max load probably less than 100w what would be the point of using 1.5mm²
  6. retiredsparks

    retiredsparks Super Member

    The biggest weakness of 1mm is that the rough brass screws on some accessories just bite through it.... unless very careful.
    5 quids difference on 100 meters ... hardly bank breaking on rewire cost.... 2 cups of coffee in cafe.
    (altho I have been taking advantage of Spoons...Doombar @£1.49 a pint and coffee at 1.15 with free refills !...and the coffee is even good enough for the lady of the house)
    Dr Bodgit likes this.
  7. Pollowick

    Pollowick Screwfix Select

    Not far out, 16A clipped direct and 11.5A enclosed in conduit in an insulated wall and 1.5mm is 20A & 14.5. Using 11.5A at 230V you get 2.6kW and that is a lot of light using incandescents/halogens - assuming the MCB did not trip.
  8. Pollowick

    Pollowick Screwfix Select

    What about the CPC on 1.5mm T&E that is 1.0 - do you get many problems with that?
  9. Coloumb

    Coloumb Screwfix Select

    ...1.5mm...and the cpc is still 1mm so this problem is avoided how... ;):)
  10. JP.

    JP. Screwfix Select

    Guys thanks to all and good stuff. Right ok I would be happy to use the 1mm on downstairs and upstairs lighting, thus one 6 amp breaker for each. Right I always keep my bath/shower rooms on a dedicated breaker so this would load up with fan, obviously light and shaver socket etc, I cannot envisage using the 1mm for that (even though total loading is well below what even 2/3 amps) and would not go less then 1.5mm for this?
  11. Pollowick

    Pollowick Screwfix Select

    Think about the loading in the bathroom with maybe 4x35W halogen plus 30W for a fan and another 20W for the shaver socket add in say 20% extra, just in case and you will get 230W or just 1A so why not?
  12. Coloumb

    Coloumb Screwfix Select

    Sounds a bit ott to me mate, in the past I've just spurred off on a 3a, had lights, fan and shaving running off that and never had a problem and used 1mm (The HORROR!!!) I guess if you want Blackpool illuminations in there then maybe...
  13. retiredsparks

    retiredsparks Super Member

    As I said ... the problem with a 1.0 mm solid conductor.......L, N or E or strapper............ is as described. IMHO
    Everyone is free to use what they wish.
  14. retiredsparks

    retiredsparks Super Member

    Well what I use to do is fold over to give the screw something to bite on if it were just one conductor being terminated. That's just me.
    Dr Bodgit likes this.
  15. Bazza-spark

    Bazza-spark Screwfix Select

    Hi JP. In domestic would always use 1.0mm, however in the factory we use 2.5mm in trunking and conduit.

    When I started (1973, 14th Edition), we were taught that 1.0mm would handle up to 10 lights based on all lights being fitted with 100W lamps. With these now obsolete and halogens, led's and the like taking over it should never be a problem.

    Just what I was taught and still do.

    Kind regards
  16. leesparkykent

    leesparkykent Well-Known Member

    I can't even remember what he last time I even used 1.5mm T&E on domestic work.
  17. With retired sparks on this.
    I have always used 1.5,it is better to work with than 1.0mm and will keep on doing so.
    I always double over the cable when only one in the terminal.
    From what I have seen different areas of the country seem to have their preference for what they use.
    KIAB likes this.
  18. KIAB

    KIAB Super Member

    Another one for 1.5mm, I also always double over the conductor, when only one in the terminal.
  19. Joe95

    Joe95 Screwfix Select

    What's the reasoning for using 2.5mm?
  20. unphased

    unphased Screwfix Select

    Factories are huge in comparison to houses. Lighting loads are vastly higher. 2.5mm2 is more appropriate. Smaller cables would increase the numbers of circuits needed amongst other things such as volt drop.
    Joe95 likes this.

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