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T-T Switch & End Switch

tivo Member Posts: 16
What are T-T switch & end switch?  I googled them but couldn't find much good resources.  Thanks!!


  • Tim McElwain
    Tim McElwain Member Posts: 4,593
    T T is not a switch

    it is the designation for the terminals on a relay that the thermostat typically is connected to. The thermostat becomes the switch. Connected to the T T terminals in the relay are a transformer in series with an electromagnet. So the transformer secondary (24 volts) is the source, the electromagnet is the load and the thermostat tied to T T is the switch.

    An  end switch is found usually on zone controls it is typically a normally open switch until and operating force is applied. The operating force would be a call for heat from a thermostat which is connected to a let us say a Zone Valve. The valve motor is powered and then as it opens to allow the flow of water through the end switch makes and could also be tied into that T T terminal on a relay which in turn will bring on a circulator and also power an oil burner or gas valve depending on which system you have.
  • tivo
    tivo Member Posts: 16
    edited May 2012
    T-T Terminal & End Switch

    Thanks for the detailed explanations.  Thanks again, Tim!!
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