Outdoor PIR light issues

Discussion in 'Electricians' Talk' started by pennye, Feb 19, 2020.

  1. pennye

    pennye New Member

    Hi all, I suspect I've caused this issue, can anyone help!? My PIR outdoor light is misbehaving and overly sensitive all of a sudden. It goes off but quickly turns itself back on without any obvious trigger.
    This light, I'm guessing, is wired into the back of this switch though has never been controllable from it https://community.screwfix.com/threads/lightwave-rf-2-way-smart-dimmer.220523/#post-1777214
    Can anyone help with what I can do to solve this?
    I'm not 100% the issue has been happening since I changed the switch, I've only noticed it the last few days, but it seems too coincidental.
     
  2. titch2k6

    titch2k6 New Member

    This will probably be a long post - sorry :)

    Let's deal with one thing first. After reading your post from the link above, you have what is called a two-wire system on the two-way lighting - and an additional single core I can't fathom out, but will get to that.

    A two-wire system is exactly that - you have two cables controlling the two-way switching. The first cable is the interlink cable and has 3 cores - grey, brown and black (sheathed brown). These connect the two switches together. Grey is COMMON, and Brown and Black are known as strappers and run between L1 and L2 on both switches. One switch will typically have these three cores ONLY. Two of the other cores (one each in L1 and L2) are your LIVE and Switch Wire and normally come down in another single cable to the other switch giving you five cores in total - this makes up your two cables (do not confuse 'cables' with 'cores'!). So how does it all work?

    The main lighting feed goes to a junction box and then out to the next light fitting - the lighting feed loop. Another cable (LIVE and NEUTRAL) runs from the switched live and neutral in the JB to the light fitting. From the JB, a LIVE core comes down to the switch carrying the power to (hopefully!) L1. Depending on the configurations of the switches, different things happen:

    1. Switch ONE open - Switch two open: The electricity travels down the L1 strapper to the second switch, as it is the only way for the electricity to flow, but can go nowhere as the contacts are open on switch two, so the lights remain OFF
    2. Switch ONE open - Switch two closed: The electricity travels down the L1 strapper to the second switch, through the now-closed contact to COMMON, back through the COMMON cable to switch one, through the contact to L2 and back to the JB through the switch-wire, turning the light on.
    3. Switch ONE closed - Switch two open: The electricity travels through the closed contact from L1 to COMMON (it cannot travel down L1 and return as switch 2 is open), down the COMMON strapper to the second switch, through the closed contact to L2, back through the L2 strapper back to switch one and back to the JB through the switch-wire, turning the light on.
    1. Switch ONE closed - Switch two closed: The electricity travels down the L1 strapper (and the COMMON strapper) to the second switch, but can go nowhere as the L2 and COMMON contacts are now open, so the lights remain OFF

    Still with me? Phew!

    The issue I have is that in your original post and picture, your L1 has an ADDITIONAL brown cable. Without looking and tracing this physically, I am guessing that this MAY be an additional switch wire for your PIR for manual over-ride. If that is the case, and you have placed this onto a Smart dimmer, that is your issue. PIRs really do not work well on dimmers, let alone 2-way circuits. It could be a feed wire, but this would make no sense as it would be easier just to take from the main lighting loop, so I have ruled this out. IF this is a switch wire, it would also explain why the PIR is activating on its own with no trigger. The over-ride is activating the unit and booting up the PIR.

    To rectify this, look in the PIR itself and see if SL (normally will have L, N and SL connections) is wired. If so, betting bottom dollar that is our mystery brown core. If so, you will lose manual over-ride, but disconnect it and make safe. Should sort out your issue.
     

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