Hello,

I am replacing a Plug-In class II transformer, PRI 120V 60 HZ .59A, SEC 16.5 V 50VA for a very old burglar alarm. There is a red and a green wire that emerges from the main panel and was connected to the old transformer (which also had a ground option, but nothing was connected there). I have lost my notes as to which side of the transformer (left or right) each wire was connected.

Should the green go on the left or the right, or does it matter? I know nothing about this stuff, so am so grateful for your help. Thanks.

Can you see any markings on the transformer indicating plus or minus? Same question, inside the panel any markings?

New transformer: no markings, other than an 'R' on the sticker above the left screw. I can't even tell if the R pertains to the screw or is some kind of intellectual property thing ('registered').

Panel: no markings. The green wire is attached to a contact to the left of the red wire although, confusingly, there is one additional wire that is attached to each of those contacts as well.

Old transformer to be replaced: three screws. Left and right say 'AC', center says 'grd' (ground). There was not a wire attached to the ground.

I apologize for using the description 'screw' rather than the proper term, which I guess might be 'contact', but I don't want to confuse the issue by using a term improperly. By screw, I mean literally what the wire attaches beneath to connect to the transformer.

I hope this information might prove helpful.

Hopefully someone will be along who can give you a procedure for testing the polarity. Taking a step further, the additional wires hooked to the incoming wires ("one additional wire that is attached to each of those contacts as well.") Any chance of tracing those wires to the device they power and looking for a plus/minus designation on that device?

Okay, I had an electrical engineer take a look-- said that both contacts were AC which means they were interchangeable and hooked it up and it works!

Thanks for your help!

Makes sense. I had DC on the brain. All's well that ends well.

Thanks, SC. Really appreciate you taking the time to help. Cheers!