Wait a cotton pickin minute here. 600.5(A) is not one of those vague subject to interpretation Sections of the code. Pretty straight forward."The outlet(s) shall be supplied by a branch circuit rated at least 20 amperes that supplies no other load." I don't care where the sign is, inside or outside, the rule applies. It should be noted that this has nothing to do with the show window lighting. Why would any inspector choose to break the rules?
600.5(A)
