Is there a restriction on a door size to a utilty closet w main electric panel- Is an 18' door OK?

For a home an 18" should be OK. The code only says:
At least one entrance of sufficient area shall be provided to give access to and egress from working space about electrical equipment.

Thank you stanfortyman! Very nice site. I appreciate the effort by everyone to offer their time and expertise.

Are you relocating the panel from somewhere else or are you building this utility closet around the existing panel.

I believe the minimum access would be a 24" door. But, I believe that applies to electrical equipment rooms, not in a residence. Also, have you reviewed the required space requirements for electrical equipment and made sure the panel is actually in an approved location?

Just one more nit-picky comment and I do mean nit-picky. NEC does not allow circuit breakers in closets, so are you sure that the contents of the closet will not prevent the panel from being placed there.

NEC does not allow circuit breakers in closets, so are you sure that the contents of the closet will not prevent the panel from being placed there.I must be nit picky here. :D

This is a long standing fallacy Don. There is no blanket prohibition of panels in closets.
The restriction is on overcurrent devices (circuit breakers and fuses) and the code simply states:
(D) Not in Vicinity of Easily Ignitible Material. Overcurrent devices shall not be located in the vicinity of easily ignitible material, such as in clothes closets.

Stan,

Huh, "NEC does not allow circuit breakers in closets"

Isn't that what I said?

Yes Don, that is what you said. It is not completely accurate though. The NEC does allow circuit breakers in closets, just "not be located in the vicinity of easily ignitible material, such as in clothes closets."

See what I am getting at?

Since this sounds like a small enclosure, built around a breaker panel shouldn't someone point out that there needs to be a 30" wide by 36" deep clear space around the breaker panel.

Yes, I read that it is being called a utility closet and yes I know that the question asked was only about the door.