2 x Lighting circuit feeding one light?

Discussion in 'Electricians' Talk' started by BikerChris, Nov 22, 2021.

  1. BikerChris

    BikerChris Active Member

    Morning all,

    I noticed a weird thing in my gaff the other day.

    If I wanted to turn off the fuse for the downstairs lights, I have to turn off TWO fuses? What's all that about then?

    2018-08-28 10.50.59-C-screwfix-forum.jpg

    So if 1 and 2 is on: LAMP ON
    1 and 2 off: LAMP OFF

    Weird that? I haven't checked through the house, only the pendant lamp in the same room as the CU.
  2. rogerk101

    rogerk101 Screwfix Select

    Is there a stairwell switched light somewhere in the house?
  3. BikerChris

    BikerChris Active Member

    Yes there is, 2-way and the staircase is in the same room as the fusebox and strangely fused lamp.
  4. seneca

    seneca Screwfix Select

    There's probably a 'borrowed neutral' there somewhere.
    BikerChris likes this.
  5. BikerChris

    BikerChris Active Member

    Ah. Would they have done that if it was getting too crowded in the hole?

    P.S. fellow beemer ride here :)
  6. MGW

    MGW Screwfix Select

    Although we call it borrowed neutral, really it is a borrowed line. two-way-real.jpg If you look at two way wiring there is a line taken to both switches, so years ago where you had two gang switches instead of using three core and earth they used two core and earth and took the line from the adjacent switch. And as long as using the same circuit this worked, although it can cause problem with hearing aids etc, as broadcasting 50 Hz, but no one knew about that then.

    Where the problem lay was latter some one wants to split the lights into two circuits as use of down lighters and the like has resulted in over 5 amp being used, and most ceiling roses are also used as junction boxes and only rated 5 amp so can't use 10 amp overload even when up to 16 amp allowed for lighting.

    So two options, combine both lighting circuits, or ensure proper split. The problem is we now consider it a safety feature to have lights split into two circuits, idea is we will not loose all lights together. This is more important as we fit RCD protection, as more likely to have a RCD trip.

    Clearly with the old Wylex box no RCD protection yet, but at some point your likely to have some thing where the manufacturer states it is required, shower, boiler etc. And also SPD fitted. There is some debate both with RCD and SPD as to if really required, but some time in the future likely will be forced on you, and better to up grade to your time scale than be forced due to needing some new appliance which stipulates them.

    P.S. Note 100 amp marked on fuse, thought the main switch on the old Wylex rated 60 amp?
  7. Tony Goddard

    Tony Goddard Screwfix Select

    Yes, normally the Wylex incoming switch is rated at 60A, later ones occasionally 80A. The Henley fuse carriers came with the 100A label on, often whats inside is a lower rating.

    Why none of the cut out manufacturers (and basically there are only two, Henley & Lucy) made, or indeed make the carrier with a window or from clear plastic so the fuse within can be seen enough to tell its rating is a mystery!

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