Many municipalities around here are at least a code cycle behind in adopting the current NEC. My question is as follows.

When the more recent code becomes more stringent the city cannot enforce that code until they have adopted that edition, right? What about the flip side to that. If the current code relaxes a requirement and a contractor installs per this new not a stringent rule, does the city have to accept it even if they have not adopted that cycle? Or is it up to their discretion wether to accept it or not? Just curious what everyone's take is on this.