My department limits the amount of coursework that can be taken based on how much you're working. That's the official stance at least. I'm sure they'd prefer that you dedicate all of your time to your research, but they can't do much about it if you need to work. They do only allow for six years of post-masters work, you have to petition the school to continue working after that.
Is the 47 credit hour requirement a post-bachelors or post-masters requirement? It seems really high to me; my department requires a minimum of 21 credit to reach candidacy past the masters level. This is in engineering though, so the requirements could be very different for Com.