FREE NEC Electrical Questions and Answers

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An institution, office, or person in charge of upholding a code or standard's standards or of authorizing tools, supplies, setups, or procedures.

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In the context of codes and standards, an Authority Having Jurisdiction (AHJ) is an organization, office, or individual that is responsible for enforcing the requirements of a specific code or standard within a given jurisdiction. The AHJ may be a government agency, local building department, fire marshal, electrical inspector, or any other entity designated by local regulations.

Which of the following can be supplied by circuits with a maximum nominal voltage between conductors of 120 volts?

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The auxiliary equipment of electric-discharge lamps, cord-and-plug-connected or permanently connected utilization equipment, and the terminals of lampholders can be supplied by circuits not exceeding 120 volts, nominal, between conductors.
This implies that these specific types of equipment are designed to operate at voltages up to 120 volts between conductors. This voltage limitation is likely to be specified for safety and compatibility reasons, as higher voltages can pose increased risks and require additional safety measures. It is essential to follow the manufacturer's guidelines and relevant safety standards when installing and using such equipment to ensure proper functionality and prevent potential hazards.

The manual switch for controlling the emergency lighting systems in a movie theater is usually permitted to be located .

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The requirements of Article 520 apply buildings used as a theater or for a similar purpose. Section 520.8 mandates the control of emergency systems in theaters to comply with the rules set forth in Article 700; Part V of Article 700 applies to the control of emergency lighting circuits. Section 700.21 does not permit a manual control switch for emergency lighting to be placed in a motion picture projection booth or on a stage or platform; the switch shall be located in the lobby or at a convenient accessible location. Emergency lighting systems are designed and installed to maintain a specific degree of illumination for means of egress of the building in the event of fire, or similar emergency, or if the normal power supply fails.

In the case of a commercial building, each of the four (4) size 2 AWG THWN insulated copper current-carrying conductors in a service-entrance conduit with a length of six (6) feet has an allowable ampacity of.

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To solve this problem first locate the conductor size on the left side of Table 310.15(B)(16) and look under the copper THWN column with a temperature rating of 75°C and note the ampacity of the conductors is 115 amperes. The table is based on an ambient temperature of 86°C and not more than 3 current-carrying conductors in the raceway. In this situation there are 4 current-carrying conductors in the raceway therefore, we must apply the correct adjustment factor (derating value) as shown in Table 310.15(B)(3)(a) as follows: 2 AWG THWN ampacity = 115 amperes (before derating) 115 amperes x 80% (adjustment factor) = 92 amperes

The maximum permissible cord-and-plug-attached load to a 125-volt, 15-ampere receptacle connected to a 120-volt branch circuit supplying two (2) or more receptacles or outlets is .

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Article 210 provides the general rules regarding branch circuits. Branch circuit and receptacle ratings are addressed in Part II of Article 210. To prevent overheating receptacles, a receptacle shall not supply a total cord-and-plug-connected load in excess of the maximum specified in Table 21(B)(2), where connected to a branch circuit supplying multiple receptables or other outlets. This table shows a 15-ampere rated receptacle may carry a maximum cord-and-plug-connected load of 12 amperes under this condition.

If ground-fault protection is not provided, it is permitted to ground the meter enclosure to the ____________ conductor on the load side of the service disconnect for a building or structure when the meter enclosure is adjacent to the service disconnecting.

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Part VII of Article 250 covers the general requirements for methods of equipment grounding. Exception No.2 to Section 250.142(B) permits the meter enclosure to be grounded by connection on the load side of the service disconnect where (1) no ground-fault protection is installed, (2) the meter enclosure is adjacent to the service disconnecting means, and (3) the grounded service conductor is not smaller than the size specified in Table 250.122.

All single-phase, 125-volt, 15- and 20-ampere receptacles installed within six (6) feet of the top inside edge of the bowl of sinks located in _____, must have GFCI protection for dwelling units.

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Section 210.8(A)(7) confirms that no matter what the location or room in a dwelling, where the 15- or 20-ampere, 125-volt eceptacles are installed within six (6) feet from the top inside edge of the bowl of the sink, GFCI protection must be provided to prevent a ground-fault shock hazard.

When a 200-ampere rated busway is tapped from a 600-ampere rated busway in industrial facilities only, what is the maximum permitted length of the 200-ampere busway if overcurrent protection is not provided for the 200-ampere busway?

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Part II of Article 368 governs the permitted installation of busways. For busways in industrial establishments only, providing overcurrent protection at the point where the busway size is changed is not required if the busway having the smaller ampacity does not exceed fifty (50) feet in length and has an ampacity of at least one-third the rating of the overcurrent protection of the larger usway. 1/3 of 600 amperes = 200 amperes Reference Section 368.17(B), exception

What is the maximum permitted voltage between conductors on a branch circuit serving luminaires in a residence?

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The maximum allowable voltage between conductors on a branch circuit supplying luminaires (lighting fixtures) in a residence is 120 volts.
In residential electrical installations, the standard voltage for most lighting circuits is 120 volts, which is typically provided through a single-phase alternating current (AC) supply. This voltage is considered safe for residential use and is commonly used to power lighting fixtures, outlets, and other devices in homes.

The same _________ shall contain all conductors of the same circuit, the grounded conductor when used, and all equipment grounding conductors and bonding conductors.

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According to the National Electrical Code (NEC), conductors of the same circuit should generally be contained within the same raceway.

For use in PV source circuits within the PV array, single-conductor cable such as _____ and single-conductor cable listed and labeled as solar photovoltaic (PV) wire are permitted.

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Part IV of Article 690 covers the wiring methods specified for use on solar photovoltaic (PV) systems arrays. Section 690.31(C)(1) indicates open, single-conductors such as Type USE-2 and single-conductor cable listed and identified as PV wire are permitted for use in PV source circuits within the PV array. These conductors are evaluated and listed for use where exposed to sunlight and wet conditions.

All switches and circuit breakers that are used as switches must be installed so that the operating handle is not more than _________ above the working platform or floor when it is in its highest position.

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According to the National Electrical Code (NEC), all switches and circuit breakers used as switches must be located so that the operating handle, when in its highest position, is not more than 6 feet 7 inches (or 2.0 meters) above the floor or working platform.

Metal water pipes shall be bonded to _____ when they are put in or attached to a building or structure.

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Part V of Article 250 covers the requirements for bonding of electrical installations. Section 250.104(A)(1) requires metal water piping systems to be bonded to any of (1) the service entrance enclosure, (2) the grounded conductor at the service, (3) the grounding electrode conductor. Where mechanical and electrical connections are within equipment, a failure of electrical insulation can result in the connected piping systems becoming energized. For example, an insulation failure in an electrical circuit of a water heater could energize the metal water piping. Metal water piping systems must be bonded so that when a fault occurs between an ungrounded (hot) conductor and the piping, the potential difference between the two is minimized, thereby reducing the risk of electrical shock. Also, note where installed in or attached to a building or structure, all metal piping systems, including gas piping, that is likely to become energized shall be bonded to a grounded source. [250.104(B)]

When Type AC armored cable is installed parallel to the sides of rafters, studs, or floor joists in an accessible attic, .

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The installation specifications for armored cable, Type AC, are addressed in Part II of Article 320. Section 320.23(B) makes it explicit, where the armored cable is installed parallel to the sides of rafters, studs or floor joists, neither guard strips nor running boards shall be required to protect the cable in accessible attics. As per Section 320.23(A), if the cables run across the top of the floor joists in an attic that is not accessible by permanent studs or ladders, protection of the cable is required where within six (6) feet of the nearest edge of the scuttle hole or attic entrance.

When installing cable or raceway-style wiring in visible or concealed places through bored holes in joists, rafters, or other wood members, the edge of the hole must be at least _________ inches from the closest edge of the wood member. Where the required distance cannot be achieved, a steel bushing or plate that is at least _________ inches thick and that is installed to cover the area where the wiring is located must be used to prevent nails or screws from penetrating the cable or raceway.

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When a cable or raceway-type wiring method is installed through bored holes in joists, rafters, or wood members in both concealed and exposed locations, the National Electrical Code (NEC) requires that the edge of the hole be at least 1.25 inches or more from the nearest edge of the wood member. This rule helps to prevent damage to the wiring due to penetration by nails or screws.
In cases where it is not possible to maintain the 1.25-inch distance, additional protection must be provided to safeguard the wiring. This protection can be achieved by using a steel bushing or plate that is at least 0.0625 inches thick (1/16 inch) or more. The bushing or plate should be installed to cover the area where the wiring is located, providing a barrier against potential nail or screw penetration.

When a ground-fault current exceeds the limits set for a Class A device, a mechanism designed to safeguard employees can de-energize a circuit or a section of it within a set amount of time.

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A Ground-Fault Circuit Interrupter (GFCI) is a type of electrical protection device designed to quickly de-energize a circuit when it detects a ground-fault current, which is a current that flows from an energized conductor (live wire) to a grounded surface or a person. This happens when there is an unintended path for the current, such as through a person who becomes part of the electrical circuit.

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