We all know that a regular control (like a Hight limit switch or a fusible link) is located on the hot side (not common) of a line-voltage circuit. However, I noticed that certain DDC output (24 vac), the control relay is on the common side (embedded in the board). Why is that?
Whice takes me to my next question. Take a generic VAV actuator like a Siemen GDE131. The drawing shows 24vac on the common wire.
When I apply 24vac to common and (let's say) drive open. (Drive close is not hook-up) I would read 24vac between drive close and common. I'm thinking this has something to do with the control relay being on the common side.