How should I attach a C wire on the chromalox boiler

boilerhvacthermostat-c-wire

I have a chromalox canada boiler model EDB-2. Recently I purchased a wireless honeywell transponder and thermostat, and am trying to install them. I currently have W and R wires but am missing a common ground C wire, and am unsure where to connect it. I have 18/3 and 18/5 spare wires.

I've enclosed photos of the inside of the boiler. The LV terminals are numbered T1, T2 and 1-5.

An HVAC consultant was able to supply power to the honeywell transponder. Unfortunately when we attempted to use the thermostat, the transponder lost power. The HVAC consultant felt that the boiler could not supply sufficient power.

So how can I connect the transponder to the boiler?

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Best Answer

According to the wiring diagram, the transformer should be installed between the T1 and T2 terminals. Though you have not shown the wiring in any of the photos, so it's difficult to give a better description than that.

However, since the transformer is only rated at 40 VA (volt-ampere), the maximum current on the secondary side of the transformer would only be 1.66666667 amperes.

40 VA / 24V = 1.66666666666667 amperes

In most cases the only things on the secondary side of the transformer are switches and relays, so this usually is sufficient. When you go installing thermostats that draw more current than that, you start running into problems.

If you want to install a thermostat that requires constant power, you may have to upgrade the transformer and any fuses that protect it.

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