ICC T16 Master Electrician Exam (2020 NEC)

A surge arrester limits surge voltages by discharging or bypassing surge current and prevents continued flow of follow current while remaining capable of repeating these functions, whereas an SPD limits transient voltages by diverting or limiting surge current.

Per Article 100 an inverter is equipment that changes dc to ac, while a rectifier performs the opposite function (ac to dc); a transformer changes voltage levels within the same current type and a dc-to-dc converter changes dc voltage/current levels.

Switchgear is completely enclosed on all sides and top with sheet metal (except ventilating openings and inspection windows) containing primary power circuit switching and/or interrupting devices with buses and connections, while a switchboard is generally accessible from the rear and not intended to be installed in cabinets and a panelboard is designed for assembly in a cabinet (a motor control center principally contains motor control units).

For ungrounded circuits, voltage to ground is the greatest voltage between the given conductor and any other conductor of the circuit; for grounded circuits it is the voltage between the given conductor and the grounded point or conductor.

For a one-family dwelling the feeder disconnecting means shall have a rating of not less than 100 amperes, 3-wire, while all installations other than one-circuit, two-circuit, or one-family dwelling feeder disconnects require a rating of not less than 60 amperes (a detached garage supplied by a feeder falls in the 60-ampere 'all others' category unless it serves as the dwelling's main disconnect).

For installations of not more than two 2-wire branch circuits the feeder or branch-circuit disconnecting means shall be rated not less than 30 amperes, versus not less than 60 amperes for all other installations.

Under 220.82(B) the general calculated load is not less than 100% of the first 10 kVA plus 40% of the remainder, while under 220.83(A), where no additional air-conditioning or electric space-heating equipment is installed, the first 8 kVA of existing and new load is calculated at 100% with the remainder at 40%.

For AC polyphase motors other than wound-rotor, the nontime-delay fuse maximum is 300% of motor full-load current while the dual-element (time-delay) fuse maximum is 175% of full-load current.

Exception No. 1 permits the next higher standard rating (per 240.6(A)) when the Table 430.52 calculation does not correspond to a standard size, while Exception No. 2 permits an increase only where the motor fails to start, and in no case may the inverse time breaker exceed 400% of full-load current for motors of 100 A or less (300% for motors over 100 A) — the cap is the limit, not simply the next standard size.

With 7 to 9 current-carrying conductors in a raceway or cable the ampacity adjustment factor is 70 percent of the table values, while with 10 to 20 current-carrying conductors the factor is 50 percent.

Dwelling kitchen receptacles serving countertop surfaces require both GFCI protection (210.8(A)(6)) and AFCI protection for 120-volt, single-phase, 15- and 20-ampere branch circuits supplying outlets in dwelling unit kitchens (210.12(A)); in other than dwelling units, 125-volt through 250-volt receptacles on single-phase branch circuits rated 150 volts or less to ground and 50 amperes or less in kitchens or areas with a sink and permanent food-preparation or cooking provisions require GFCI protection (210.8(B)(2)).

Overhead spans of open conductors not over 1000 volts require a clearance of not less than 3.0 m (10 ft) above finished grade where the voltage does not exceed 150 volts to ground and the area is accessible to pedestrians only, versus not less than 5.5 m (18 ft) over public streets, alleys, roads, parking areas subject to truck traffic, driveways on other than residential property, and other land traversed by vehicles.