The primary power supply of a smoke detection device shall be either a commercial light and power source normally available in the dwelling unit, or an integral battery or batteries. Connection to a commercial power and light source, if used, shall be in the form of permanent wiring to terminals or leads in a separate wiring compartment having provision for the connection of a conduit, metal-clad or nonmetallic sheathed cable, by means of a power supply cord and attachment-plug cap, or by means of a separate power supply. exception: Smoke detection devices in dwelling units built or manufactured in this state after December 31, 1980, shall receive their primary power from the building wiring when such wiring is served from a commercial source. Wiring shall be permanent without a disconnecting switch other than those required for overcurrent protection.