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Honeywell RA832A XX Terminals

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AdamNJ
AdamNJ Member Posts: 3
edited January 2022 in Thermostats and Controls
Hi, newbie here, website has a lot of great information. Looking for help understanding how the XX terminals work on the RA832A. When the circuit on the TT terminals (thermostat) is closed does it also close the circuit on the XX terminals providing 24 V? Can you think about it as a normally open relay? Thanks.
Adam

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  • Jamie Hall
    Jamie Hall Member Posts: 23,297
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    AdamNJ said:

    Hi, newbie here, website has a lot of great information. Looking for help understanding how the XX terminals work on the RA832A. When the circuit on the TT terminals (thermostat) is closed does it also close the circuit on the XX terminals providing 24 V? Can you think about it as a normally open relay? Thanks.
    Adam

    T-T are the two terminals controlling the coil of the internal relay. When the circuit is complete -- the thermostat is calling for heat -- they energize the internal relay which, in turn, closes three contacts: two, the Load 1 and Load 2 pairs -- provide 120 VAC to external loads. The X-X pair is not powered at all; when the relay is energized it just closes the circuit between them.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,526
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    X & X are usually just a set of dry contacts, no power usually normally open and for use on low voltage circuits only
  • Erin Holohan Haskell
    Erin Holohan Haskell Member, Moderator, Administrator Posts: 2,284
    edited January 2022
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    Welcome, @AdamNJ. I've merged your duplicate posts into one here.
    President
    HeatingHelp.com
    EdTheHeaterMan
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,838
    edited January 2022
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    @AdamNJ Let me know if this helps clear things up

    X X are dry contacts. There is no voltage related to them think of the X X as the two screw terminals of a toggle switch. You know, like the one you would see on a wall to turn on the lights. The switch does not have any voltage associated to it. It can be rated for 400 volts but that does not mean it must be used on a 400 volt circuit. all it means is that if you want to, you could use it for that. But you could also use it 110 volts or 24 volts. It is just a switch with 2 screw terminals. As a Human Being you could operated the switch UP (usually) and close the contacts to make the light come on (or turn on the fan motor or electric heating element on the toaster), or turn the switch handle down and the LOAD would go off.



    The Human Being part of the switch is the T T terminals as illustrated by this diagram



    In the diagram one of the T terminals is connected to a 24v transformer that is then connected to the relay coil (that is the part that takes the place of the Human Being in this switch). The other path of the Relay Coil is connected to the other T terminal. when a thermostat is connected to T T on this relay, the R and W terminals on the thermostat are just like the toggle switch as illustrated here

    The human being part of the switch in the thermostat is automatically activated by temperature. On a heating thermostat R and W close when the room temperature falls below the set point of the thermostat. When the room temperature rises above the setpoint, the R and W switch opens. That is why I say the human being part of the switch is the room temperature.

    Now why would you select this control over say a R845A control? That is easy, Back in the day, a plumber might use this because he could be working on a heating system that has an oil burner one day and a gas heater the next day. If that gas heater has a Millivolt control system, the X X terminals are rated for Millivolt or low voltage (not Line Voltage). So he could use the same relay to bring on the circulator using contact #3 for the circulator 110 V circuit and the X X for the gas valve circuit.

    The next day he could use the same control to add a circulator to a gravity boiler system with an oil burner. #3 terminal can operate the circulator pump and the #4 terminal could operate the oil burner circuit. Since plumbers were not supposed to be the greatest electricians, they only needed to learn one relay that could do everything they needed. (remember back in the day meant when plumbers were adding circulators to gravity hand fired boiler that were converted to gas or oil burners.)

    Many a plumber's customers were SHOCKED when they found their plumber was not the greatest electrician! (if you think that Dad Joke is funny you can hit the LOL button below) Keeping it simple for the Plumber was the reason Honeywell designed the R832A. And they sold a ton of them!

    Mr. Ed
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • AdamNJ
    AdamNJ Member Posts: 3
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    Thank you all, this has been very helpful and @EdTheHeaterMan the additional context is interesting too. Now that I own a home with steam heating system and scavenger loop this website has become the most useful resource. Appreciate all your help and sorry for the delay in responding having a 2 year old and 2 month old at home keeps me busy.
    Adam