Control Transformer for DDC control

[techzone12]

We are installing VAV controllers in the ceiling plenum of a building. The controllers require 24V and each one is 10 VA rated.

How big of a 24V transformer can we install in the ceiling plenum to provide power to the controllers? What are the limitations by the NEC code? If the controllers, as an example, going to draw 5 amps total, is this allowed by the code?

Thanks

 

[davidbeach]

Have you talked with the electrical engineer on the project?

 

[wirenut60]

be careful... i think that would be a class 2 transformer, (it's been a while since i last checked code on this)... but the largest acceptable transformer for DDC controls in an environmental air plenun is 96va. If i can find the manufacturer and part number, i will post it. I originally put 200va transformers in for DDC controls and the local AHJ quickly corrected me. The solution and what the AHJ approved was a 96va transformer.