Here's an example of an HVAC transformer that will go from 120 or 240 to 24 VAC.
Obviously, all wires exit the device through the same pipe nipple; the device is intended to be installed by screwing it onto a junction box using that nipple:
Since installing like that pretty much requires that the high & low voltage wires & respective splices are made together, how can this be used in a code-compliant (not to mention generally safe) way?
It seems clear from other questions here (and other reading) that high & low voltage wires are meant to be kept apart for good reason. (ex1, ex2)
I've seen other types which segregate the high & low voltage wires, but if this transformer was what you had available, what are the options?
Best Answer
I'd simply take this transformer back and get a different one
The transformer you have was designed for use as a replacement transformer inside HVAC equipment, hence the design with primary and secondary wires in the same nipple. However, this also means it's RU (UL Component Recognized, or Rather Useless to us) instead of being UL listed, which isn't helpful in our situation. I'd take this back and get a different transformer with a full UL listing and a different wiring arrangement; in the Johnson Controls lineup, the Y65T21-0 or Y65T31-0 would be suitable substitutes, depending on the mounting arrangement you're working with. (They also provide an extra "blind" terminal on their secondary side that can be used as a general wire-connection point.)