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Transformer with RWG Terminals. Sequence of Operation

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HydroTech23
HydroTech23 Member Posts: 2


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  • HydroTech23
    HydroTech23 Member Posts: 2
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    This is an original American Standard Transformer that supplies voltage to the gas valve. I need to replace it but its so old I cant find it.
  • Steamhead
    Steamhead Member Posts: 16,835
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    What is the secondary voltage and VA?
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Consulting
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,837
    edited April 3
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    This is the replacement https://www.supplyhouse.com/Resideo-AT72D1683-Foot-Mounted-Plate-Mounted-or-Clamp-Mounted-120-Vac-Transformer-w-9-in-Lead-Wires-40VA
    Steamhead said:

    What is the secondary voltage and VA?

    A close look at the black cover shows 40VA

    Some assembly is required since this is a multi-mount universal transformer.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,837
    edited April 3
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    Why did the transformer fail? Could be old age. OR there could be a failed section of wire insulation causing a dead short. If that is the case, you will be purchasing a second transformer if that short circuit is not corrected before connecting the new one.

    Try adding a fuse to the R terminal, then connect the red wire to the other side of the fuse. Like This
    I don't really sell these, Just get some fuses and wire connectors from the auto parts store.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • 109A_5
    109A_5 Member Posts: 1,385
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    Hello @HydroTech23,
    Looks like 24 VAC at 10 VA on the cover plate. So a transformer with the same secondary Voltage and the same VA rating or greater should work as long as there is no system defect that cause the original transformer to fail.





    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System
  • Sylvain
    Sylvain Member Posts: 122
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    for a 24V transformer, chose the fuse (on the low voltage side) with a rating lower or equal to I=VA/24.
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,524
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    Looks to me like with R<W & G the old one is a fan center with maybe a relay on the other side that is not being used.