Is their any code requirements for using fire rated plywood. Here in CT I have seen 1/2" plywood painted with just gray paint. I have always used 3/4" fire rated. Thanks.

I can't say if there is a NEC article (because I'm too lazy to look), but it may be covered by city codes. Many services and panelboard "walls" I have done - in NJ - have been mounted on wood with fire proof paint (black). It's gotten to the point I don't ask if it's required, I just do it. Some supply houses here have actually started carring fire-proofed plywood cut into a 2'x4' sheet

So you just use 1/2" painted with gray or black fire proof paint.

Around here (DC/MD/VA metro) we use 3/4 ply. Just generic stuff, not fire rated. I've never heard of anybody being turned down. I guess 1/2 would also be ok but for me it's too thin to get the screw to hold well.