Underground service conductors of not over 1,000-volts that are not encased in concrete and that are buried 18 inches or more below grade, shall have their location identified by a warning ribbon that is placed in the trench at least _____ above the underground installation.

The Master Electrician exam in most electrical licensing examinations covers these topics: Grounding and bonding, Overcurrent protection, Wiring methods and installation, Boxes and fittings, Services and equipment, Motors, Special occupancies, Load calculations, Lighting, Appliances, Box and raceway fill, Hazardous locations, Trade knowledge and Electrical theory.