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C wire

Timmmy
Timmmy Member Posts: 14
in Thermostats and Controls
Picked up the Honeywell T9 through my utility.  It came along with the C wire adapter kit. What would be the cleanest way to add it to my Steam boiler. Attached is the transformer in the boiler itself. There's also an external transformer which power the old stat.

Comments

  • Zman
    Zman Member Posts: 7,611
    Which transformer is the t-stat wired to?
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Timmmy
    Timmmy Member Posts: 14
    It's wired to a transformer that was installed external of the boiler on the ceiling 
  • HVACNUT
    HVACNUT Member Posts: 6,338
    If there's a separate transformer for a thermostat, then there must also be an isolation relay. Does the existing thermostat use the Common?
  • Timmmy
    Timmmy Member Posts: 14
    I don't think there's an isolation relay....thermostat was getting about 37 volts. 
  • ChrisJ
    ChrisJ Member Posts: 16,317
    What boiler is this?
    Do you have the wiring schematic?

    Can you pull a new wire from the boiler to the thermostat?

    Single pipe 392sqft system with an EG-40 rated for 325sqft and it's silent and balanced at all times.

  • STEVEusaPA
    STEVEusaPA Member Posts: 6,505
    Why does a steamer need a T9?

    There was an error rendering this rich post.

  • Timmmy
    Timmmy Member Posts: 14
    edited July 2021
    Burnham IN6
     I have a tekmar 564. I did run a new Stat wire to the upstairs since I gutted the floor.  The stat with remote sensor was like $50 from the utility. I want a wifi stat with remote sensor since the first floor is a tenant space.
  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 4,215
    I would junction onto the yellow wire from the transformer in that there junction box.


    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • HVACNUT
    HVACNUT Member Posts: 6,338
    37 volts. You might need boots on the ground for that. Unless you can draw out exactly where every low volt wire is going. 
  • Timmmy
    Timmmy Member Posts: 14
    edited July 2021
    That's why I was looking for advice. Seeing if the other transformer is necessary. Tracing out the wires Shouldn't be too bad....
    Thanks for the comments
  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 4,215
    HVACNUT said:

    37 volts. You might need boots on the ground for that. Unless you can draw out exactly where every low volt wire is going. 

    Can you elaborate? Why would a thermostat see such high voltage from a dedicated 24-volt transformer?
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • Timmmy
    Timmmy Member Posts: 14
    The way its wired,  its picking up from both transformers. I'll check it out when I get home later
  • HVACNUT
    HVACNUT Member Posts: 6,338
    Alan (California Radiant) Forbes said:
    37 volts. You might need boots on the ground for that. Unless you can draw out exactly where every low volt wire is going. 
    Can you elaborate? Why would a thermostat see such high voltage from a dedicated 24-volt transformer?
    Could be a bad neutral or ground, a faulty transformer or faulty wiring. 
    Alan (California Radiant) Forbes
  • Mike_Breault
    Mike_Breault Member Posts: 35
    Good day, Mike Breault from tekmar here, if you only have 2 wires, there are a couple options, depending Ion access, if you're ok with the stat in the room, a tekmar 564 only needs 2 wires, and has isolatable switches for heat call. if you do not want access to stat, use the 2 wires for a remote sensor like a tekmar 084 with a 518 (non wifi) or a 561 (wifi capable) thermostat.

    with either system you can use the boiler transformer, or a seperate one as the heat relay on all stats can be isolated for applications where there are 2 power supplies.

    Be well
  • Timmmy
    Timmmy Member Posts: 14
    edited July 2021
    I think the schematic is similar to Alan's. Can't read it too clearly....

    R & C on the stat are fed from the external transformer getting 27 volts

    RH1 on the stat is going to BLUE on the transformer

    W1 is going to BROWN  

    As I mentioned before, a new Stat wire has been run, so the 2 wires are not a problem. I'd like to clean it up a bit if possible. 

    Thanks everyone!
  • Mike_Breault
    Mike_Breault Member Posts: 35
    @Timmmy if the Mech interface module is powered from a seperate transformer, move the J3 jumper pin to OFF. otherwise your boostiong your transformers.. the R and Rh1 are internally connected with J3 in the ON position.

    Best
    Mike Breault, tekmar

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