Are you sure about them pulling 4/0? If you have a 200 amp service now you should already have 4/0 AL. Usually the PoCo installs 350 AL for 400 amp residential services and requires a 3" or 4" duct. Make sure you have this correct or your customer may be without power for a long time if the PoCo comes out to connect it and tells you that it can't be done until you install a new duct to the street.
