Voltage Free Relay question

Discussion in 'C-Bus Wired Hardware' started by AnotherCluelessUser, Dec 21, 2021.

  1. AnotherCluelessUser

    AnotherCluelessUser

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    Hi all,

    Just moved into a house with an old (16 years-ish) cbus system, one of the rooms (en-suite bathroom) recently stopped working and im going slightly insane trying to figure it out.

    One of my many questions is, on the relay each output has an a and a b (1a 1b, 2a 2b etc..) - is there a differerence between these? The current wiring that is relevant is:

    7a - output to main bathroom and a wire linking to 8a
    7b - output to main bathroom

    8a - wire linking to 7a
    8b - output to en-suite bathroom that doesnt work

    I dont understand the bridge between 7a and 8a or why its suddenly stopped working - everything else is fine. The light comes on solid green on the relay when button is pressed both on the switch and from the relay

    Also - is there a good source of documentation about the relays that anyone has? Everything i've looked at is pretty basic.

    Thank you!

    Mark
     
    AnotherCluelessUser, Dec 21, 2021
    #1
  2. AnotherCluelessUser

    Ashley

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    The relays are voltage free outputs. i.e the 'a' and 'b' are the two connections to the relay and are isolated from everything else. Generally one is connected to the power input, and the other to the load. In most installs the power comes into the active of the relay then links one side of all of the relays. This will be your 7a and 8a connections. They are not an output to the main bathroom but the power coming in. When a relay closes it connect the a and b output which connects the incoming power to the load. The a and b are interchangeable.

    Given channel 7 works, you must be getting power coming in. If you hear the relay click when you activate channel 8, then that channel is likely working also. So it is most likely a downstream problem with the load (i.e. the en-suite bathroom. It is possible that the relay has failed, but unlikely if you can hear it click.

    One common problem is the wire connections to the relays can loosen over time if they weren't tightened to spec in the first place.

    Relays are about a basic as it gets. When activated they connect the a and b terminals together. What else do you want to know?
     
    Ashley, Dec 21, 2021
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  3. AnotherCluelessUser

    AnotherCluelessUser

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    Well, im an idiot who didnt understand the concept of a voltage free relay, thank you so much it all makes far more sense now. I will get my meter out and do some digging later. Really appreciate your help thank you
     
    AnotherCluelessUser, Dec 21, 2021
    #3
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