Cindy,
During my time in the military I was taught that ANY metal to metal contact of different types should be handled with care. I witnessed things that I never thought possible (box openings being oxidized to dust in a matter of weeks due to dissimilar metals). If you can avoid contact it is just a good thing to do. You will save yourself headaches and callbacks.
This also takes into account what kind of environment that the project is located in. The above mentioned example was in Korea where the climate was conducive to corrosion. They (my boss at the time) went so far as to have different types of metal brushes purchased to avoid dissimilar metal contact during routine Preventive Maintenance Inspections.
I am not aware of any code that states it but it would be a good practice to follow.
Hope this helps…
