Checking whether a wire is live, neutral or switched live...

Discussion in 'Electricians' Talk' started by enfield21, Feb 6, 2010.

  1. enfield21

    enfield21 New Member

    Hi,
    Please see below for full story...Another suggested all should be fine to plug the wires I have into the Salus stat as long as I can confirm which is live, which is switched and if the earth is connected. Any ideas how I can do this based on the facts below?

    My old Honeywell T40 room thermostat has lost the will to live so the plan is to upgrade it to the Salus RT300.
    My problem is this. Currently the T40 is connected as follows - a black wire goes to terminal 1, a red wire goes to terminal 3 and the earth goes to the earth. That's it, no other wires, no other colours. First concern is that, despite the T40 seeming to work fine in the past, the red and the black wires are connected round the wrong way - is this the case? Second concern is that the Salus wants me to connect a live wire and a switched live wire - what's happened to red is live and black is neutral? I'd assumed that the red wire is live and that the black wire is neutral - is this not the case? To confuse me even more, a plumber (who had been in servicing our boiler) said that the black wire was in fact a load wire... So is it neutral, load or switched live? Or are load and switched live the same thing?
    Please help...
  2. seneca2

    seneca2 New Member

    Assuming the red is permanently live(which you can easily check) the black will be the load,or switched live. There should also have been a neutral but many people omit this.The stat was only working as an on/off switch so it wouldn't have matered which way round the wires were.
  3. enfield21

    enfield21 New Member

    Thank you for that. How can I check what each wire is doing? - bearing in mind that I'm your bog standard DIYer!!
    What is the worst that could happen if I put the red wire onto the live terminal, the black into the switched live and the green into the earth?
    Regards
  4. JP.

    JP. Screwfix Select

    Is the red really permanently live though Sen..is it not controlled by the programmer?..ie it could be live or not depending on prog status.
  5. seneca2

    seneca2 New Member

    I mean it's permanent live for the stat when the system's on JP and that's all that matters really.
  6. JP.

    JP. Screwfix Select

    Sorry Sen.
  7. seneca2

    seneca2 New Member

    enfield, if you only have 2 wires you obviously haven't got a neutral there or it would never have worked in the past. If you only have 2 wires it won't really matter which way round you put them, it's only working as a single pole switch.
  8. enfield21

    enfield21 New Member

    Okay, that makes sense thank you.
    So I'm safe to connect red to live, black to switched live and green to earth?
    And to confirm - load and switched live mean the same thing?
  9. JP.

    JP. Screwfix Select

    Sen would it not be best to verify that the CPC is in fact a CPC and not one which has been used for you know what?
  10. enfield21

    enfield21 New Member

    What is "you know what"?
  11. seneca2

    seneca2 New Member

    Good point JP. enfield, some people very naughtily use the earth wire as a switched live! Just make certain that the earth wire was in fact connected to the earth terminal in the original stat.
  12. enfield21

    enfield21 New Member

    I can confirm that the green wire is connected to the earth on the old stat.
  13. seneca2

    seneca2 New Member

    Good, away you go then harry!
  14. enfield21

    enfield21 New Member

    I'm going in - fingers crossed...
  15. JP.

    JP. Screwfix Select

    Not being funny or owt..but make sure you observe correct isolation procedures.

    By the way is that Enfield, the Enfield near Waltham Cross?
  16. enfield21

    enfield21 New Member

  17. enfield21

    enfield21 New Member

    Thanks for your help. Nothing blew up and everything seems fine. Lights and numbers on. Let's just hope we don't freeze in the night...
  18. JP.

    JP. Screwfix Select

    Hmmmmm..lights and numbers on..

    Are you sure this wasn't a wind up Enfield?

    ;)
  19. seneca2

    seneca2 New Member

    I think you might be right JP, I see the Salus 300 has a digital display, how's that gonna work without a neutral?
    (not when the contacts are closed anyway!)
  20. Teuchter

    Teuchter New Member

    Pssst, it's battery powered...

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