Junction boxes

Discussion in 'Electricians' Talk' started by st, Oct 22, 2003.

  1. st

    st New Member

    Hi

    thanks for all your help on previous questions.

    I am looking at the lighting in my house, and it is based on the junction box system.

    I spent about 4 hours diligently drawing the existing junction box wiring (with the electric off) and i think i have the principle of how its done.

    I have j/b's with 4 terminals - each of which seem to control 2 lights (ie one JB supports the kitchen light and switch, and the living room light and switch)

    What i am trying to suss is 'is there a correlation between the number of terminals in a JB and the number of 'switched lights' it can handle'?

    not sure if i phrased this correctly and i am going to get a pro in - but i just wondered if there was a rule of thumb about this.

    After searching for Juncton boxes on the net i mainly got responses relating to pages for model railway enthusiasts!

    cheers again and sorry if my questions have the professionals out there holding their heads in their hands

    si
     
  2. poolethetool

    poolethetool New Member

    Your jb's as you put it have four wires one is the switch wire one is the light wire and the other two are the circuit wires which are connected to each room usually one lighting circuit downstairs and one lighting circuit upstairs. if in doubt call out a sparky!.
     
  3. screwfox

    screwfox New Member

    Hi

    thanks for all your help on previous questions.

    I am looking at the lighting in my house, and it is
    based on the junction box system.

    I spent about 4 hours diligently drawing the existing
    junction box wiring (with the electric off) and i
    think i have the principle of how its done.

    I have j/b's with 4 terminals - each of which seem to
    control 2 lights (ie one JB supports the kitchen
    light and switch, and the living room light and
    switch)

    What i am trying to suss is 'is there a correlation
    between the number of terminals in a JB and the
    number of 'switched lights' it can handle'?

    not sure if i phrased this correctly and i am going
    to get a pro in - but i just wondered if there was a
    rule of thumb about this.

    After searching for Juncton boxes on the net i mainly
    got responses relating to pages for model railway
    enthusiasts!

    cheers again and sorry if my questions have the
    professionals out there holding their heads in their
    hands

    si

    The terminals required for 1 light are as follows:

    1 - Live in (from consumer unit or previous Junction Box)
    Live out (to next junction box, not required if last junction box), this is called the loop live.
    Live to switch

    2 - N in (as live in above)
    N out (as live above)
    N to light fitting(s)

    3 - Live from switch, called the switched live
    Live to light fitting

    For 2 lights, 4 terminals will be required, with terminal 4 being wired the same as terminal 3 above, but for the second switch/light fitting

    For 3 lights, 5 terminals will be required, with terminal 5 being wired as per 3 and 4 above

    Continue, ad infinitum, so the number of terminals required can be expressed as (number of light circuits + 2).

    In practice, you will usually find a ceiling rose used, which is really only a 3 terminal junction box, feeding a single light circuit, with all the ceiling roses linked together.

    Hope this helps
     
  4. CDRW

    CDRW New Member

    The 4th terminal in the JB is used to connect the earth wires together and therefore cannot be used to operate two lighting circuits.

    Continue, ad infinitum, so the number of terminals
    required can be expressed as (number of light
    circuits + 2).

    Which makes your formula number of terminals = number of light circuits + 3.
     

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