Today, I saw a DC coil relay operate perfectly fine (as far as we could tell) with reverse polarity on the coil (+24V on A2 and an open drain input on A1, sinking).
I always assumed that polarity was critical with DC relays, causing current to flow in a specific direction through the coil, magnetizing the core/coil and pulling the armature in a specific direction. I would figure that reversing polarity on the coil would repel the armature, not making the contacts.
I then started thinking about AC coil relays, and while I'm familiar with the phase shift properties of the shading coil. I realized that polarity through that coil would shift back and forth. I know the shading coil causes a phase shift that is present to keep flux in the coil at all times.
So, now I wonder:
Should a DC coil relay work in reverse polarity? Why?
Despite the shading coil, why wouldn't the flux shift direction eventually, and cause a momentary state of zero-magnetism?
Thanks to any and all that can help me here. This has been somewhat humbling.