This is an irc building code. Mobile home industry stopped use in 1974 with the implement of HUD. Supply or service cable is still aluminum. This is usually 100 amp or 200 amp. And referee to in cable size as ott. Ie 2- ott. Aluminum wire is not as conductive as copper. And aluminum is subject to becoming brittle in time and when overheated. Or overloaded. Resulting in connections to become loose.