I think a hybrid of the approaches here would be a good idea. Go ahead and install the breaker ($45, big deal) in the spirit of cooperation, noting how you can understand his position on the code. But as others here said, don't be a pushover either. With code book in hand, let him know your knowledge of the code, and diplomatically prove how he was incorrect in his determination.
Now you have put him on notice for the future, and at the same time assured your job will pass.
Sometimes you've just pick your battles. Something small like this just isn't worth a big battle. And remember your customer, and more importantly your reputation as an EC. The customer won't be too thrilled if your doesn't get signed off on quickly... and over what, a $45 breaker?
Joe
