Kansas City, MO Low-Voltage Electrician Exam (ICC G21, 2017 NEC)

Per NEC 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 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 Class 1 power-limited circuits meeting the power limitations of 725.41(A) or Class 1 remote-control and signaling circuits used for remote-control or signaling and meeting 725.41(B).

Per the NEC 760.2 definition, fire alarm circuits are classified as either non–power-limited or power-limited, and the classification determines the applicable installation requirements (e.g., NPLFA raceway fill follows 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 separate electrode, 820.100(D) requires a bonding jumper not smaller than 6 AWG copper (or equivalent) between that electrode and the power grounding electrode system, whereas 14 AWG is the minimum size for the shield bonding/grounding electrode conductor itself under 820.100(A)(3).

Per NEC 250.104(B), other metal piping systems, including 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 required by 250.104(A).

Per NEC 820.44(A)(4) Exception, where proximity to electric light, power, Class 1, or non-power-limited fire alarm conductors cannot be avoided the clearance is 1.0 m (40 in.) at the pole while a minimum of 300 mm (12 in.) is required at all other points along the drop; similarly, 800.44(A)(4) allows 300 mm (12 in.) separation at any point in the span for 0–750 V 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.

Per NEC 725.43, overcurrent protection shall not exceed 10 amperes for 16 AWG and shall not exceed 7 amperes for 18 AWG, while 14 AWG and larger conductors are protected in accordance with conductor ampacity.

Per 800.170(A), the listed primary protector consists of an arrester connected between each line conductor and ground in an appropriate mounting with terminals marked line and ground, whereas a fuse in series with each line conductor is a feature of the fused-type primary protector described in 800.90(A)(2).

Series resistances add directly (R1 + R2 + …), while parallel resistances combine as 1/Rp = 1/R1 + 1/R2 + 1/R3 (or product-over-sum for two resistors), giving a value smaller than any single branch.

Table 250.66 sizes the grounding electrode conductor from the largest ungrounded service-entrance conductor (e.g., over 3/0 AWG through 350 kcmil copper requires 2 AWG copper), while per 250.28(D) the main bonding jumper shall not be smaller than the sizes shown in Table 250.102(C)(1).

For separate protection of 14 AWG and larger conductors, Note 1 directs the user to the ampacity value specified in 310.15, whereas the 400 percent and 300 percent multipliers of Notes 2 and 3 apply only where the motor branch-circuit short-circuit and ground-fault protective 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.

Lead-in conductors attached to buildings shall not be able to swing closer than 600 mm (2 ft) to conductors of circuits of 250 volts or less between conductors, the clearance from any conductor of a lightning protection system shall not be less than 1.8 m (6 ft), and indoor antennas/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/cable armor or permanently separated by a continuous, firmly fixed nonconductor.