ICC G21 Low-Voltage Electrician Exam (2017 NEC)

Per Article 100, the main bonding jumper is the connection between the grounded circuit conductor and the equipment grounding conductor at the service, while the system bonding jumper makes that same type of connection (to the supply-side bonding jumper, the equipment grounding conductor, or both) at a separately derived system.

Per NEC 725.41, Class 1 circuits are classified as either power-limited circuits meeting the power limitations of 725.41(A) or remote-control/signaling circuits used for those functions and meeting 725.41(B); 'inherently limited/not inherently limited' instead describes Chapter 9 Table 11 power source constructions.

Article 760 classifies every fire alarm circuit as either non–power-limited or power-limited, and that classification determines the applicable installation requirements (e.g., NPLFA raceway fill must comply with 300.17 per 760.3(J), while PLFA cable per 760.179(I) shall not be marked with a voltage rating except where multiple listings require it).

Where a CATV system uses its own grounding electrode, the jumper to the power grounding electrode system shall be not smaller than 6 AWG copper (or equivalent), whereas 14 AWG is the minimum size for the shield bonding/grounding electrode conductor itself.

A control circuit fed from a separate panelboard is protected as a Class 1 circuit under 725.43 (10 A max for 16 AWG, 7 A max for 18 AWG, ampacity for 14 AWG and larger), while tapped control conductors larger than 10 AWG use the 400 percent and 300 percent multipliers of Table 430.72(B) Notes 2 and 3 (Columns B and C).

With separate overcurrent protection for 14 AWG and larger control conductors (e.g., 12 AWG copper), Note 1 directs the maximum rating to the conductor ampacity value from 310.15, while the 400/300 percent multipliers apply only where the motor branch-circuit short-circuit and ground-fault device protects control conductors larger than 10 AWG; the 500 percent figure belongs to 430.72(C)(4) for control transformer primaries rated less than 2 amperes.

Other metal piping systems such as gas piping that are likely to become energized must be bonded to the equipment grounding conductor of the circuit likely to energize the piping, which differs from the metal water piping bonding requirements of 250.104(A).

Lead-in conductors attached to buildings shall not swing closer than 600 mm (2 ft) to power conductors of circuits of 250 volts or less between conductors and shall be not less than 1.8 m (6 ft) from any lightning protection system conductor, while indoor antennas and indoor lead-ins shall not be run nearer than 50 mm (2 in.) to conductors of other wiring systems unless those conductors are in metal raceway or cable armor or permanently separated by a continuous, firmly fixed nonconductor.

For coaxial lead-in/overhead drops where proximity to light, power, Class 1, or NPLFA conductors cannot be avoided, 820.44(A)(4) requires 1.0 m (40 in.) at the pole and a minimum of 300 mm (12 in.) at all other points; similarly 800.44(A)(4) requires 300 mm (12 in.) minimum separation at any point in the span for 0–750 volt supply drops above and parallel to communications drops, provided ungrounded conductors are insulated and not less than 1.0 m (40 in.) is maintained at the pole.

Coaxial cable is permitted to deliver power to equipment directly associated with the radio frequency distribution system only if the voltage is not over 60 volts, whereas a medium-power network-powered broadband source has a circuit voltage Vmax of 0–150 volts and its entrance cables must be in a listed raceway or fittings suitable for the purpose.

In a series circuit the total current equals the current in any other part of the circuit (IT = I1 = I2 = I3), while parallel resistors combine as product-over-sum for two resistors or as the reciprocal sum for more, producing a total resistance lower than any branch.

In a 120/208-volt three-phase four-wire wye system, any phase conductor to the grounded neutral measures 120 volts while any two phase conductors measure 208 volts.

Per NEC 110.6, conductor sizes are expressed in American Wire Gage for conductors up to 4/0 AWG and in circular mils (kcmil) for conductors larger than 4/0 AWG.