Journeyman Electrician's NEC Flashcards

A single conductor must be at least ____ AWG in size when utilized in power-limited fire alarm circuits.

Answer: 18

According to NFPA 70, the National Electrical Code (NEC), specifically Article 760 for Fire Alarm Systems, conductors used in power-limited fire alarm circuits must be no smaller than 18 AWG. This minimum size ensures adequate mechanical strength and current-carrying capacity for the low-power signals essential in these critical safety systems.

A supply-side bonding jumper of ____ AWG will be used for a service with 500 kcmil conductors on a 400 A service.

Answer: 1/0

To determine the correct size for a supply-side bonding jumper, NEC Table 250.102(C)(1) is referenced. For a service with 500 kcmil conductors, the table specifies a minimum bonding jumper size of 1/0 AWG. This ensures that the bonding jumper can safely carry the fault current and maintain proper electrical continuity.

The top and bottom of stairways must have listed wall-mounted control devices if there are ____ or more steps between each floor.

Answer: Six

NEC 210.70(A)(2)(c) mandates that listed wall-mounted control devices must be installed at both the top and bottom of stairways. This requirement applies when there are six or more risers (steps) between floor levels. This ensures convenient and safe control of lighting, preventing individuals from having to navigate steps in darkness to reach a switch.

A maximum of _____' between supports is required for type MV cables to be supported.

Answer: 6

According to NEC 328.30, Type MV (Medium Voltage) cables must be securely supported at intervals not exceeding 6 feet (1.8 m). This requirement is crucial for maintaining the structural integrity of the cable installation, preventing excessive sagging, and ensuring long-term reliability of the electrical system.

With the exception of ____, all 120 V, single phase, 15 A, and 20 A branch circuits feeding outlets or devices installed in housing units must be AFCI protected.

Answer: Garages

NEC 210.12(A) requires Arc-Fault Circuit Interrupter (AFCI) protection for most 120-volt, single-phase, 15- and 20-ampere branch circuits supplying outlets or devices in dwelling units. However, garages are explicitly listed as one of the locations that are exempt from this AFCI protection requirement in dwelling units.

It is necessary to have at least one or more equipment grounding wires that are ______ AWG on a raceway that includes multiple 15 A circuits.

Answer: 14

According to NEC Table 250.122, the minimum size for an equipment grounding conductor for a 15-ampere branch circuit is 14 AWG copper. Even when multiple 15 A circuits are run in a single raceway, the equipment grounding conductor size is determined by the largest overcurrent device protecting any circuit, which in this case is 15 A, thus requiring 14 AWG.

Any location with ____ is classified as a Class II location.

Answer: Combustible dust

NEC Article 500.5(C) defines Class II hazardous (classified) locations as those where combustible dust is present in the air in quantities sufficient to produce explosive or ignitable mixtures. This classification is essential for selecting appropriate electrical equipment and wiring methods to prevent ignition in such environments.

A single phase 120 V, 0.5 HP induction motor's current rating is ____ A.

Answer: 9.8

To determine the full-load current for a single-phase AC motor, NEC Table 430.248 is used. For a 120-volt, 0.5 HP (1/2 HP) single-phase induction motor, the table specifies a full-load current of 9.8 amperes. This value is critical for correctly sizing the motor's conductors and overcurrent protection devices.

The smallest conductor that can be used for a ground ring is ______ AWG.

Answer: 2

NEC 250.52(A)(4) specifies that a ground ring electrode must consist of at least 20 feet of bare copper conductor, and this conductor must be no smaller than 2 AWG. This minimum size ensures adequate conductivity and mechanical strength for the ground ring to effectively dissipate fault currents into the earth, providing a reliable grounding path.

On the same load, two power fuses over 1000 V may be connected in parallel as long as the two fuses are Identical.

Answer: have the same rating

NEC 240.8 generally prohibits connecting overcurrent devices in parallel. However, an exception is made for fuses rated 1000 volts or over, provided they are 'identical in rating and characteristics.' This ensures that the parallel fuses share the load equally and operate simultaneously under fault conditions, preventing an imbalance that could lead to premature failure or inadequate protection.

In any hazardous (classified) location as defined in Articles 500.5, 505.5, and 506.5, the electrical continuity of normally non-current carrying metal parts of electrical equipment, raceways, metal clad cable, and other metal enclosures shall be _______ regardless of the electrical system's voltage.

Answer: Bonded

In hazardous (classified) locations, it is imperative that all normally non-current-carrying metal parts of electrical equipment, raceways, and enclosures are effectively bonded. This bonding creates a continuous, low-impedance path to ground, which is crucial for preventing the accumulation of static electricity and ensuring that fault currents are safely cleared. This measure significantly reduces the risk of ignition in potentially explosive atmospheres, regardless of the system's voltage.

The system _____ jumper is fitted at the same location on each individually derived system where the connections for the grounding electrode conductor are established.

Answer: Bonding

A system bonding jumper is essential in individually derived systems, such as those with separately derived transformers. It connects the grounded conductor (neutral) to the equipment grounding conductor and the grounding electrode conductor at the point of derivation. This ensures that all non-current-carrying metal parts are bonded together, creating a low-impedance path for fault current and facilitating the operation of overcurrent protective devices for safety.

There will be a voltage drop of _______ V in a single phase, 240 V circuit with 3 AWG AI conductors powering a 40 A load 300' away from the power panel.

Answer: 9.67

To calculate voltage drop (VD) for a single-phase circuit, the formula VD = (2 * K * I * L) / CM is used. Here, K (resistivity constant for aluminum) is 32.6, I (current) is 40 A, L (one-way length) is 300 ft, and CM (circular mils for 3 AWG aluminum) is 52,620. Plugging these values into the formula yields VD = (2 * 32.6 * 40 * 300) / 52,620 = 9.67 V. This calculation is crucial for ensuring efficient operation and compliance with electrical codes.

Systems that operate at voltages between conductors of ______ volts or more are ungrounded, and this must be clearly indicated at the _____ of the system.

Answer: either A or B

Ungrounded electrical systems operating at 50 volts or more between conductors must be clearly identified for safety reasons. This identification alerts personnel to the unique characteristics and potential hazards of an ungrounded system during a fault. The National Electrical Code (NEC) mandates that this indication be present either at the system's source or at its first disconnecting means, ensuring visibility and awareness.

At _____, secondary tie circuits must feature overcurrent protection.

Answer: both ends

Secondary tie circuits interconnect different secondary networks and require robust overcurrent protection for safety and reliability. To ensure that any fault on the tie circuit is quickly isolated and cleared, overcurrent protective devices must be installed at both ends of the circuit. This prevents power from feeding into a fault from either direction, protecting equipment and personnel.

The equipment grounding conductor for a heating element protected by a 40 A inverse time circuit breaker must be at least _____ AWG.

Answer: 10

The size of the equipment grounding conductor (EGC) is determined by the rating of the overcurrent protective device (OCPD) protecting the circuit, as specified in NEC Table 250.122. For a heating element protected by a 40 A inverse time circuit breaker, the minimum required size for a copper equipment grounding conductor is 10 AWG. This ensures the EGC can safely carry fault current back to the source, allowing the OCPD to trip and clear the fault effectively.