Master Electrician Questions With Verified Answers

A 150 kVA service transformer has a 480Y/277 volt 3-phase primary and a 208Y/120 volt, 3-phase secondary. What is the approximate full-load ampere rating of the primary of the transformer? - Answer 180 amperes Where a conductor is marked RHW-2 on the insulation what does the "-2" represent? - Answer The conductor has a maximum operating temperate of 90 degrees C. For a grounded electrical system supplied by a feeder or branch circuit, the equipment grounding conductor shall be sized in accordance with _____. - Answer the overcurrent protective device For lighting systems operating at 30-volts or less, the output circuits of the power supply are to be rated for NOT more than _____. - Answer 25 amperes Using the standard method of calculation, what is the demand, in kW, on the ungrounded (line) service-entrance conductors of an apartment complex that has thirty-five (35) electric ranges rated at 11.5 kW each? - Answer 50 kW Where a service riser is installed in a wet location and contains THWN insulated conductors, the wiring method used _____. - Answer is permitted to be electrical metallic tubing (EMT) What is the MAXIMUM distance between supports for straight horizontal runs of trade size 1½ in. threaded rigid metal conduit (RMC)? - Answer 14 feet Overcurrent protection of transformers, of 600 volts or less, is required to be sized _____. - Answer in accordance with Table 450.3(B) A thermal barrier shall be required if the space between the resistors and reactors, of 600 volts or less, and combustible material is LESS than _____. - Answer 12 inches In movie theaters, all switches for controlling the emergency lighting systems shall be located _____. - Answer in the lobby Where a 90 ampere, 240-volt, single-phase load is located 225 feet from a panelboard and is supplied with size 3 AWG copper conductors, determine the approximate voltage drop on the conductors. (K = 12.9) - Answer 10 volts Wiring methods associated with solar photovoltaic (PV) systems shall not be installed within _____ of the roof decking or sheathing except where directly below the roof surface covered by PV modules and associated equipment. - Answer 10 inches All metallic switchgear rated for over 600 volts shall be provided with a grounding busbar for the purpose of connecting the _____. - Answer metallic shield of cables Conductors tapped from a feeder and supplying the primary of a transformer need not have overcurrent protection, where the length of the tap conductors are not over 25 feet and have an ampacity of at LEAST _____ of the rating of the overcurrent device protecting the feeder conductors. - Answer one-third Electrical equipment such as switchboards, panelboards, industrial control panels, and motor control centers, located in commercial and industrial occupancies are required to be field marked to warn _____ of potential electrical arc flash hazards. - Answer qualified persons When connecting utilization equipment to a 20-ampere rated branch-circuit that also serves luminaires (lighting fixtures), the utilization equipment shall have an ampere rating of NOT more than _____. - Answer 10 amperes Where a hotel has a stationary electric sign installed inside a decorative fountain, the sign shall be at LEAST _____ inside the fountain, when measuring from the outside edges of the fountain. - Answer 5 feet In an aircraft hanger, the area that extends upward from the floor level _____ above the upper surface of aircraft wings, power plants and fuel tanks shall be classified as a Class I, Division 2 or Zone 2 location. - Answer 5 feet Conductors supplying outlets for arc and xenon motion picture projectors of the professional type shall be a MINIMUM size of _____. - Answer 8 AWG Where rigid polyvinyl chloride (PVC) conduit is installed underground to supply a gasoline dispensing unit, threaded rigid metal conduit (RMC) or threaded intermediate metal conduit (IMC) shall be used for the LAST _____ of the underground run to where the conduit emerges. - Answer 2 feet Where electrical metallic tubing (EMT) is installed under metal-corrugated sheet roofing decking, a clearance of at LEAST _____ must be maintained between the top of the tubing and the surface of the roof decking. - Answer 1 1/2 in.