Steel to Copper Union With a Plastic Fitting

Galvanized Steel to Copper Union With a Plastic Quick Connect Fitting

I have a Watts (SeaTech) WaterPex 3/4" CTS x 3/4 MPT plastic fitting. Can this be used in place of a dielectric union between galvanized steel & copper? The 3/4" MPT side would screw into a steel female thread, and the other side would accept 3/4" copper pipe (quick connect). Since the fitting is plastic, and the two dissimilar metals don't touch, isn't this a defacto dielectric union?

Technically, yes. But since the "electrolysis" is conducted THROUGH the water, the proximity of the two metals is just as important as whether they actually touch. This is also the reason why most "dielectric unions" are cosmetic rather than functional, as would yours.