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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    Most of the wiring in the images you've provided seems to be 120V wiring. Take a look at this image. I've highlighted some of the things in the wiring diagram, and shown them in the actual wiring. The item circled in red is the transformer, that's where the power is stepped down from 120V to 24V. There should be more wires attached to that device, which are the secondary (24V) side wires. These wires are what's used by the control circuitry (thermostat). – Tester101 Dec 11 '13 at 12:28
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    No need to pre-shrink your pictures, we're using a technique from imgur.com that automatically shrinks pictures when you add an l, m, or s to the end of the filename (large, medium, small). With the pictures pre-shrunk, we can't allow others to click through to see the full size image. – BMitch Dec 11 '13 at 16:15
  • It's difficult to tell what's going on based on you photos, but I would guess the black and white wires attached to T1 and T2 are from the transformer? The red wires attached to T1 and T2, attach to capacitors somewhere? – Tester101 Dec 11 '13 at 16:42
  • Are you sure of the model number? I'm not able to find it listed anywhere. – Tester101 Dec 11 '13 at 17:41

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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  • Thanks Tester101. We had a renovation done in our basement and apparently the thermostat wires were compromised which blew our transformer. At that time, we had 3 wires going to an old thermostat with a clock that was not battery operated. The HVAC company came and installed a new transformer and a battery operated honeywell beside the boiler which is not ideal. They said we had to hire an electrician to course wires through the wall (ruining our new dry wall). I noticed that the new wiring he installed only had 2 wires, one black and one white – user18553 Dec 11 '13 at 15:08
  • When it lost power, were any fuses blown, or did parts have to be replaced? – Tester101 Dec 11 '13 at 17:25
  • No parts were replaced. The HVAC person just said that because of this, the transponder was not meant to be used with a boiler and should be used with a furnace instead. He then rewired the black and white (R and W) wires to the battery operated thermostat originally provided by them. – user18553 Dec 11 '13 at 17:30
  • I'm not sure we'll be able to provide any help over the internet. Unfortunately, you'll likely have to contact a different HVAC person. – Tester101 Dec 11 '13 at 17:34

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