Need to power CA8900

Other Devices & Integrations Climate Control & Temperature Sensors
1

I am trying to figure out how to power my ‘C’ wire.

I hooked it up to the 24 volts coming off the transformer on the board in the boiler room and the thermostat works but then dies until I disconnect and reconnect it.

Do I need to run 2 wires? On another job where there is no power at all I ran a transformer that had 2 wires which i ran the to C and RH on the thermostat and it works great.

Why can you you run only one wire to the C on some systems but have to run 2 when u use a dedicated transformer?

here is the board in the boiler room I want to power off of. You can see I jumped a blue/c wire over to the transformers red wire, do i need to run another from the rh to the yellow?

http://img163.imageshack.us/img163/5153/cimg5684large.jpg

2

To power the t-stat, it needs to be connected to both sides of a transformer. One side is provided through RH. The other side through C.

Do you measure ~24VAC across RH and C?

3

can i power multiple thermostats with one transformer?

i did with 8 thermostats and they all seemed to work but it seems there was crossover somehow and one thermostat would control all the zones.

4

Depends on the power draw of the thermostats. Two or three wouldn’t be outlandish… Eight? Dunno.

If you’ve got one thermostat controlling all zones, then you’ve got something other than just power (and the contact wires for the intended zone) connected to that one thermostat.

5

I wired 4 thermostats (CA8900) from a 24 vac transformer (Heath/Zenith) that I pickup from home depot for around 12.00. No problem. I had to run a seperate wire for the C but attached the other on to the RH at the air handler. Worked well for me. The transformer is typically used for door bells.

6

watch them closely. i thought my 8 were working fine but i had problems. I put 3 on and still had line voltage loss issues. so I went with dedicated transformers for all 8