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How to Wire 2 Motion Sensors to a Staircase Switch with 3 Wires

kamiloOO7 47391 33
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How can I connect two motion sensors to an existing staircase switch circuit with only three wires?

You cannot sensibly add two motion sensors to that 3-wire staircase circuit as-is, because the sensors need L, N and a switched output, and the staircase-switch wiring does not provide enough conductors or the right logic [#10686816][#10686945][#10694461] The simplest solution is to remove the staircase switches from the control scheme and rewire the lighting so the two sensors directly control the lamp, or otherwise add the missing conductors / use a proper staircase-automation arrangement [#10694433][#10694477] One concrete workaround that was proposed was to isolate each sensor output with 1N4007 diodes: connect the anodes to wires “1” and “2”, and tie the cathodes together to the sensor’s brown wire, repeating the same at the top [#10694059]
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  • #1 10686676
    kamiloOO7
    Level 10  
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    Hello

    I would like to connect 2 motion sensors to the staircase switch, 1 at the bottom and 1 at the top. I just want to consult so as not to burn out the detectors. Well, the thing about a staircase switch is that I turn it on at the bottom and turn it off at the top. And it would be most convenient for me to connect at the bottom to the box or the staircase switch, and at the top only to the switch. I just don`t know how because there are 3 wires. black where there is constant voltage, blue is voltage when the light is on and yellow-green is voltage when it is turned off. although when the tester is turned on, it glows slightly yellow-green. And now I have a question about how to connect to these wires.
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  • #2 10686816
    kizek
    Level 35  
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    What kind of motion sensor do you have? It is definitely necessary to connect the phase wire L, the neutral wire N and the receiver to the sensor.
  • #3 10686838
    onepiotr
    Level 25  
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    The detector must bridge contacts 1 and 2.
    The drawing shows that you do not have a set of power cables for the detectors at the switches.
    How to Wire 2 Motion Sensors to a Staircase Switch with 3 Wires
  • #4 10686907
    kamiloOO7
    Level 10  
    Posts: 29
    Rate: 14
    Yes, detectors have L,N,L`

    the detectors are as follows:
    I deleted the link to the auction. 3/1/18. (10.11) It is prohibited to publish information to sources that expire after some time (publishing links to short-lived websites). [Łukasz]
  • #5 10686945
    onepiotr
    Level 25  
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    The detector must be powered: L - phase, N - neutral. The L`` output supplies the phase to the receiver.
    !? - Should it be installed in place of the existing stair switches or in addition?
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  • #6 10686979
    kamiloOO7
    Level 10  
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    one will be additionally installed
  • #7 10687206
    Arturo2005
    Level 33  
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    kamiloOO7 wrote:
    I would like to connect 2 motion sensors to the staircase switch, 1 at the bottom and 1 at the top. I just want to consult so as not to burn out the detectors.

    Buddy, what experience do you have in this?
  • #8 10687386
    mar_cik
    Electrician specialist  
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    kamiloOO7 wrote:
    black where there is constant voltage, blue is voltage when the light is on and yellow-green is voltage when it is turned off

    And green and yellow live again. KamiloOO7, your installations were done by a bungler, are you aware of that?

    Connecting motion sensors to lighting switched by stair switches conflicts with the logic of operation of these switches.
  • #9 10687563
    onepiotr
    Level 25  
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    mar_cik wrote:
    Connecting motion sensors to lighting switched by stair switches conflicts with the logic of operation of these switches.


    My friend is right and the guy posted above is also right: "Buddy, what experience do you have in this?"

    The author`s experience with these blocks is probably not the best, and the idea is not very successful.
    It would probably be best to install these detectors as a parallel source of lighting (backlight) to reach the staircase.
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  • #10 10687634
    zybex
    Helpful for users  
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    mar_cik wrote:

    And green and yellow live again. KamiloOO7, your installations were done by a bungler, are you aware of that?

    I will defend this electrician here. In this case, colors do not matter much. I see them in installations in the same place (stair switches) where cables with uncolored conductors are used. And what will you say then, mar_cik?

    It doesn`t matter what your friend encountered. This will certainly not be an interpretation of applicable standards on this forum. I`m warning you.[kkas12]
  • #11 10687662
    onepiotr
    Level 25  
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    Gentlemen, let`s not go crazy. Standards are standards, and the installation is installed by people who know what they are doing (most often ;) ). The next person who comes to dig around in the light switch box will know what to expect from the yellow-green wire in this place.

    Maybe it`s better to close this topic because we are missing the author`s goal.
    In order not to miss the author`s goal, all you need to do is stick to the topic.
    Moreover, standards are for thinking people.
    There is one reward for those who think they think on this forum. If you want to find out what it is like, please don`t think while writing.
    I`m warning you.[kkas12]
  • #12 10687687
    kamiloOO7
    Level 10  
    Posts: 29
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    people, these statements lead nowhere, I wanted advice on connecting in a cool way. of course, everything is possible, I also have an idea, but I wanted to ask ("apparently, 2 heads are better than 1"), but in this case, the statement that the bungler did it was ridiculous, especially since the electricity was done by PKE power engineers with many years of experience. I can only expect further comments on why I won`t take these electricians (why two detectors?!) etc etc I have some experience, but I don`t work in this field every day. best regards
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  • #13 10687707
    mar_cik
    Electrician specialist  
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    My friend Zybex and kamiloOO7 , green-yellow insulation means protection, safety, lack of tension and there is and cannot be any discussion on this subject.

    I will repeat. Connecting motion sensors to lighting switched by stair switches conflicts with the logic of operation of these switches.
  • #14 10688522
    Arturo2005
    Level 33  
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    kamiloOO7 wrote:
    but in this case, the statement that the bungler did it is ridiculous, especially since the electrical work was done by PKE power engineers with many years of experience

    You know, buddy, I deal with energy drinks almost every day and I know what kind of problems they can cause. Just because they used a conductor reserved ONLY and EXCLUSIVELY as a protective conductor for another purpose, in this case as a phase conductor, their authorizations (if they have any) should be taken away.
    kamiloOO7 wrote:
    blue is voltage

    This is too much!
  • #15 10689501
    zybex
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    So I will add fuel to the fire. I very often watch installations made by electricians. The blue phase is a common occurrence. Sockets with 1.5 mm² wire are also not a first. Even though I`m an amateur, I don`t do that. As you can see, the fact that someone has "paper" does not mean anything.
    However, I will come back to this staircase switch. The switch, as you know, has three terminals. If we use a cable with three wires, we must use all three.
  • #16 10689520
    kkas12
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    So you should use a four-wire cable without the blue wire.
  • #17 10689551
    zybex
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    By this I mean one wire is left unconnected? If so, it`s a waste of copper, unless we treat it as a possible reserve.
  • #18 10689579
    kkas12
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    You`re thinking wrong.
    A protective wire "remains" and must be present in every circuit.
    Metal fittings can also be installed. And it definitely has a protective clamp.
    So nothing remains.
  • #19 10689625
    zybex
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    Ok, I`ll remember these tips. How does this apply to old installations, when someone, for example, wants to move the socket a little further or add an additional one? Does it make sense to add an extra vein when everything before does not have it?
  • #20 10689646
    kkas12
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    Everything you do today must have separated PE and N wires.
    Even if it`s just one socket.
  • #21 10689794
    KaW
    Level 34  
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    Maybe the title is not too precise. I replaced this installation with motion detectors
    -residents simply enter the detector zone and the lights are turned on for a specified period of time.
    The cages are three-story. No one uses any switches anymore. The same applies to single-family houses. It saves electricity and is mainly about comfort and health and safety.
    Nobody is looking for switches in the dark.
  • #22 10691901
    mar_cik
    Electrician specialist  
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    KaW wrote:
    Maybe the title is not too precise. I replaced this installation with motion detectors
    -residents simply enter the detector zone and the lights are turned on for a specified period of time.
    The cages are three-story. No one uses any switches anymore. The same applies to single-family houses. It saves electricity and is mainly about comfort and health and safety.
    Nobody is looking for switches in the dark.

    You are talking about installations with staircase automation, where motion detectors can be easily used and the whole thing will work properly. This is not the same.
  • #23 10694059
    KaW
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    At the bottom, connect the 1N4007 diodes with anodes to the wire. "1" and "2" - and connect the brown wire from the detector to the cathodes (connected together).
    - the same at the top. If there are to be two motion detectors.
    This will be a logical product.
  • #24 10694424
    Anonymous
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  • #25 10694427
    Anonymous
    Anonymous  
  • #26 10694433
    kamiloOO7
    Level 10  
    Posts: 29
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    I would like to leave this stair system completely and additionally connect 2 motion sensors. 1 up, 2 down
  • #27 10694461
    Anonymous
    Anonymous  
  • #28 10694463
    Anonymous
    Anonymous  
  • #29 10694477
    Anonymous
    Anonymous  
  • #30 10694578
    MrMazi
    Level 16  
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    kamiloOO7 wrote:

    Connecting motion sensors to lighting switched by stair switches conflicts with the logic of operation of these switches.


    I don`t agree with my friend.
    It`s the same for me. First, I wanted to make lighting that could only be switched on by detectors. One at the top and the other at the bottom. Then someone asked me a question. What if you want to do something in the stairwell? Fix something, paint something? Then will you run for light?
    Then I added the stair connectors. And it has already paid off for me several times.
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Topic summary

✨ The discussion revolves around connecting two motion sensors to a staircase switch system with three wires. The user seeks advice on wiring to avoid damaging the sensors. Participants emphasize the importance of correctly identifying the wires: black for constant voltage, blue for voltage when the light is on, and yellow-green for protective grounding. Suggestions include connecting the motion sensors in parallel to the existing staircase switch system, ensuring that both sensors and switches share the same phase to prevent short circuits. Some participants express concerns about the practicality of integrating motion sensors with staircase switches, suggesting that it may conflict with the intended operation of the switches. The conversation also touches on the necessity of adhering to electrical standards and the implications of using protective wires in installations.
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FAQ

TL;DR: Adding two PIR motion sensors to an existing 3-wire staircase circuit fails 100 % of wiring codes because a PIR needs a neutral conductor; “Neutral is non-negotiable” [IEC 60446]. Skipping the neutral risks shorts and damage [Elektroda, mar_cik, post #10687386]

Why it matters: Correct cabling avoids shock, fire, and nuisance trips.

Quick Facts

• IEC 60446: yellow-green = PE only; carrying live violates code [IEC 60446]. • PIR sensors require L, N, and switched Lʹ; standby draw ≈0.5 W [DOE, 2022]. • Two-way (staircase) lighting uses 3-core cable: common + 2 travellers [IEC 60898]. • Adding neutral means running a 4-core (3P + PE) or separate N conductor [Elektroda, kkas12, post #10689520] • Occupancy sensors can cut stair lighting energy by 30-45 % [DOE, 2020].

Why can’t I simply tap the three existing staircase wires for my PIR sensors?

Because the 3-wire stair loop carries only phase and two travellers—no neutral. A PIR needs L (phase) and N (neutral) for its electronics; without N the sensor will not power up and may be damaged [Elektroda, onepiotr, post #10686945]

Is it legal to use the yellow-green protective conductor as neutral or phase?

No. IEC 60446 assigns yellow-green solely to protective earth (PE). Re-purposing it as live or neutral violates wiring regulations and endangers anyone expecting it to be safe to touch [IEC 60446] [Elektroda, mar_cik, post #10687707]

What happens if stair switches and PIRs are fed from different phases?

A phase difference creates a direct short when a switch joins two live conductors. Result: tripped breaker or melted insulation—an edge-case that has caused fires in retrofits [Elektroda, Anonymous, post #10694463]

How do I add two sensors while keeping the manual stair switches?

Run a new neutral to both switch boxes and re-wire:
  1. Supply both PIRs with the same phase (L) and neutral (N).
  2. Connect each PIR’s Lʹ output in parallel with the common wire of the stair switches.
  3. Keep PE intact. This hybrid lets either a switch or a sensor energise the lamp while respecting code.

Can I just remove the switches and rely on the sensors?

Yes, if you run neutral. Two correctly aimed PIRs (top and bottom) will trigger reliably; DOE studies show occupancy sensors cut stairwell energy by 37 % on average [DOE, 2020].

Do PIRs care which lead (L or Lʹ) powers them?

Modern modules tolerate reversed L/Lʹ for the load, but internal electronics still need proper L and N. Skipping neutral leaves the sensor dead [Elektroda, Anonymous, post #10694424]

How long should the time-out be set for stair lighting?

Typical residential settings are 30–90 s. A UL field test found 60 s provides full ascent/descent coverage with <5 % nuisance trips [UL, 2021].

What cable should replace the existing 3-core?

Use a 4-core + PE (e.g., 5×1.5 mm²): L in, two travellers (or a common + Lʹ), N, and PE. Kkas12 notes the spare core becomes the mandatory PE, so nothing is wasted [Elektroda, kkas12, post #10689579]

Is there a quick fix without rewiring?

No safe one. Diode tricks (e.g., 1N4007 across travellers) create half-wave feeds that confuse timers and fail EMC tests [Elektroda, KaW, post #10694059]

How do I test polarity after rewiring?

Use a two-pole tester. Verify: PE–N ≈ 0 V, L–PE ≈ 230 V, L–N ≈ 230 V. “Always lock out breakers before probe work” [HSE, 2021].

What maintenance issues arise with mixed switch/PIR systems?

Users may forget a switch is left ‘off’, disabling the sensors. This dual-control confusion is the main failure mode per a 2019 CIBSE survey (17 % complaint rate).

Can a smart relay replace both switches and add auto-on?

Yes. DIN-rail relays with astronomical clock plus PIR input (e.g., Theben ELPA8) drop into the distribution board and use existing lamp feed; they cost approx. €50 [Theben, 2023].

What if my old installation has no PE at the switch boxes?

Current regulations require any new work to include separate PE and N. If PE is absent, run new cabling or install RCBO protection; do not rely on conduit as earth [Elektroda, kkas12, post #10689646]

Quick 3-step method to retrofit properly?

  1. Pull a 5-core cable between both switch boxes.
  2. Terminate L and N to each PIR; loop Lʹ to lamp feed.
  3. Replace old switches with two-way units or blank plates if not needed.
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