Master Electrician Exam (NEC) flashcards

The structural metal frame of a building, if in direct contact with the earth for 10 feet or more, can serve as a grounding electrode.

• Part of a grounding electrode system.
• Must be in direct contact with earth.
• Minimum 10 feet (3.0 m) contact length.

Memory trick: Electrodes grounded deep, secrets they keep.

When multiple grounding electrodes are used, the GEC can be connected to them in a continuous run or with suitable splices, ensuring all electrodes are effectively bonded.

• GEC can be continuous or spliced.
• No specific order of connection required.
• All electrodes must be connected.

Memory trick: GEC connects all, standing tall.

When a modular home is supplied by a feeder from remote service equipment, an equipment grounding conductor must be run with the feeder, and the neutral isolated at the modular home's panelboard.

• Feeder-supplied structure.
• EGC required with feeder.
• Neutral isolated at modular home.
• Independent GES permitted/required.

Memory trick: Feeder to structure, grounding's the key, neutral's apart, for safety you see.

For No. 1 AWG copper service conductors, the GEC to a ground rod is No. 6 AWG copper.

• Direct application of NEC Table 250.66.
• Common residential service size.
• Ensures adequate fault current path.

Memory trick: Number One service needs Six for the rod.

When a grounding electrode conductor is connected to a concrete-encased electrode, it is not required to be larger than No. 2 AWG copper or No. 1/0 AWG aluminum, even if Table 250.66 would indicate a larger size.

• Found in NEC 250.66(B).
• Applies specifically to concrete-encased electrodes (Ufer grounds).
• Provides a maximum size, often resulting in a smaller GEC than otherwise calculated.

Memory trick: Ufer ground: GEC no bigger than two.

A rod electrode used as part of a grounding electrode system must be a minimum of 8 feet in length and driven fully into the earth.

• Part of the NEC 250.52(A)(5) requirements.
• Must be driven to a minimum 8-foot depth.
• Often used as a supplemental electrode.

Memory trick: Eight feet for the rod, if water pipe's not enough.

A conductor or strap that connects the neutral conductor to the equipment grounding conductor and the service enclosure at the service entrance.

• Establishes a low-impedance path for fault current.
• Required at the service equipment.
• Bonds the neutral to ground at one point only.

Memory trick: Neutral's main job is to bond the box and ground.

3-phase, 3-wire delta systems can be ungrounded, or if grounded, must have one phase conductor intentionally grounded (corner-grounded delta).

• Ungrounded delta systems require ground-fault detectors.
• Corner-grounded delta systems have one phase bonded to ground.
• High-leg delta systems (120/240V, 3-phase, 4-wire) have the midpoint of one transformer phase grounded.

Memory trick: Delta's ground: cornered or ungrounded, never floating.

Equipment grounding conductors (EGCs) are sized based on the rating of the overcurrent protective device for the circuit, as per NEC Table 250.122.

• Sized by overcurrent device rating.
• Table 250.122 is the reference.
• Ensures fault current path.

Memory trick: EGC size, fault current's demise.

The size of the grounding electrode conductor is determined by the size of the largest ungrounded service-entrance conductor or equivalent area for parallel conductors, referenced in NEC Table 250.66.

• Based on the largest ungrounded service conductor size.
• Different rules for connection to specific electrode types apply (e.g., ground rods vs. concrete-encased).
• Table 250.66 is the primary reference.

Memory trick: Service conductor size dictates the GEC's might.

A wiring system whose power is derived from a source other than a service, having no direct connection to the service conductors except through the earth, and whose neutral is grounded at the source of the separately derived system.

• Neutral must be bonded to ground at the source of the separately derived system.
• Neutral must be isolated from equipment grounding conductors downstream.
• Often applies to transformers, generators, or feeders to separate buildings.

Memory trick: Subpanel neutral: separate the white from the green, but connect to the ground bar.

The bonding jumper for a service raceway must be sized according to NEC Table 250.102(C)(1) based on the size of the ungrounded service-entrance conductors.

• Sized per Table 250.102(C)(1).
• Based on ungrounded service-entrance conductor size.
• Ensures reliable path for fault current.

Memory trick: Bonding jumpers connect, sizing must be perfect.

The grounding electrode conductor (GEC) for a service is sized based on the largest ungrounded service-entrance conductor, referencing NEC Table 250.66.

• Sized by largest ungrounded service conductor.
• Table 250.66 is the reference.
• Connects GES to service equipment.

Memory trick: GEC size, the service it ties.

The grounding electrode system of a lightning protection system must be bonded to the building's electrical grounding electrode system to ensure equipotential and prevent dangerous potential differences.

• Required by NEC 250.60.
• Prevents dangerous side flashes.
• Creates a common ground reference.

Memory trick: Lightning and power: one bond, one ground.

Electrical Metallic Tubing (EMT) is recognized by the NEC as an acceptable equipment grounding conductor when properly installed with listed fittings that ensure electrical continuity.

• Permitted by NEC 250.118(4).
• Requires listed fittings and proper installation.
• Provides a low-impedance path for fault currents.

Memory trick: EGCs: wire, conduit, or cable armor.

The main bonding jumper size is determined by the size of the largest ungrounded service-entrance conductor or equivalent area for parallel conductors, referenced in NEC Table 250.102(C)(1).

• Sized based on the largest ungrounded service conductor.
• Found in NEC 250.28(D) and Table 250.102(C)(1).
• Ensures a low-impedance path for fault current at the service.

Memory trick: Bonding jumper size: service conductors tell the tale.

A motor's service factor (SF) indicates how much overload it can safely tolerate above its nameplate full-load current (FLA) for short periods without damage. An SF of 1.15 means it can run at 115% of FLA.

• SF of 1.15 or greater allows overload device sizing at 125% of FLA.
• SF less than 1.15 (or not marked) requires overload device sizing at 115% of FLA.
• The motor can continuously draw FLA x SF without overheating.

Memory trick: Motor 'SF' is like a 'Super-FLA' boost, but a '125%' trip is the guard rail.

Conductor ampacity is the maximum current a conductor can carry continuously without exceeding its temperature rating. Overcurrent protection must be sized to protect the conductor's ampacity, often with specific limitations for smaller conductors.

• NEC Table 310.16 provides ampacities based on insulation type and temperature rating.
• NEC 240.4(D) limits overcurrent protection for small conductors (e.g., 14 AWG to 15A, 12 AWG to 20A).
• The OCPD must protect the conductor at its lowest temperature rating or the terminal rating.

Memory trick: Conductor protection is 'Amp'ly covered by 'NEC' 'Tables' and 'Limits'.

Arc-Fault Circuit Interrupters (AFCIs) are primarily required by NEC 210.12 for 120-volt, single-phase, 15- and 20-ampere branch circuits supplying outlets or devices in specific dwelling unit locations.

• NEC 210.12 governs AFCI.
• Applies to 15A and 20A, 120V circuits.
• Required in dwelling unit bedrooms, family rooms, etc.

Memory trick: AFCI 'arcs' 'fire' 'homes' from danger.

The maximum rating of a motor's short-circuit and ground-fault protective device is determined by the motor's full-load current (FLA) and the type of protective device, as specified in NEC Table 430.52.

• Inverse time breakers are generally allowed up to 250% of FLA.
• If the calculated value isn't a standard size, the next higher standard size is permitted.
• The maximum for inverse time breakers, even with the next size rule, is 400% of FLA.

Memory trick: Motor protection is a 'FLA'shy calculation, always check the 'Tab'le.

For continuous loads (expected to operate for 3 hours or more), the overcurrent protective device (OCPD) must have a rating not less than 125% of the continuous load current.

• Continuous load is 3 hours or more (NEC 100).
• OCPD must be sized at 125% of the continuous load (NEC 210.20(A)).
• Next higher standard OCPD size is permitted if 125% value is not standard.

Memory trick: Continuous loads are a '125%' commitment, so size the 'OCPD' accordingly, then go 'Next'!

The minimum interrupting rating for a circuit breaker in a residential service is typically 10,000 amperes (10 kAIC) unless the available fault current is calculated to be higher and explicitly requires a greater rating.

• Required to safely interrupt short-circuit currents.
• Residential standard is 10,000 AIC.
• Must be equal to or greater than the available short-circuit current.

Memory trick: Interrupting ratings 'break' the short-circuit 'current' to protect the 'home'.

An Arc-Fault Circuit Interrupter (AFCI) is a circuit breaker designed to detect and trip on potentially dangerous electrical arcs, thereby reducing the risk of electrical fires.

• Detects both series and parallel arc faults.
• Protects against fire hazards from damaged wiring.
• Required in specific dwelling unit locations by NEC 210.12.

Memory trick: AFCI is an 'ARC'itect of safety, building a 'FIRE'wall against sparks.

The NEC 240.21(B)(2) 25-foot tap rule permits tap conductors up to 25 feet long, provided their ampacity is at least one-third of the feeder OCPD rating, they terminate in an OCPD, and are protected from physical damage.

• Tap conductor length limited to 25 feet.
• Tap conductor ampacity must be at least 1/3 of the feeder OCPD.
• Tap conductors must terminate in an OCPD sized for the tap's ampacity.
• Must be protected from physical damage.

Memory trick: Taps are like 'short threads', '25 feet' is the limit for the '1/3' rule.

The overcurrent protective device for an individual household electric range branch circuit is sized at 100% of the calculated load, as per NEC 210.19(A)(3) and 210.20(A).

• Calculate current (I = P/E).
• OCPD at 100% of calculated load.
• Conductor ampacity must support the load.

Memory trick: Cooking 'appliances' need 'right-sized' 'power' protection.

For motor branch-circuit short-circuit and ground-fault protection using non-time-delay fuses, the maximum rating is generally 300% of the motor's full-load current (FLA) as per NEC Table 430.52.

• Applies to non-time-delay fuses.
• Maximum rating is 300% of FLA.
• Refer to NEC Table 430.52.

Memory trick: Motors need 'gears' of 'protection' from 'electrical' faults.

For continuous loads (operating for 3 hours or more), the overcurrent device must be sized at no less than 125% of the continuous load, or the continuous load must not exceed 80% of the overcurrent device rating, unless the device is 100% rated.

• Continuous load: 3 hours or more.
• OCPD must be 125% of continuous load.
• Continuous load must be 80% of OCPD rating (if not 100% rated).

Memory trick: Continuous loads need 'time' and 'extra' protection, like a 'long' journey.

The Interrupting Rating (IR), expressed in Amperes Interrupting Current (AIC), is the maximum fault current that an overcurrent protective device (OCPD) can safely interrupt without being destroyed or causing an unsafe condition.

• Must be equal to or greater than the available short-circuit current.
• A crucial safety parameter for OCPDs.
• Different from continuous current rating.

Memory trick: IR is like a 'Fault Fighter', it must be 'BIG'ger than the 'BANG' to survive.

An intrinsically safe circuit is designed to prevent ignition of flammable or combustible atmospheres by limiting the electrical and thermal energy to levels too low to cause ignition, even under fault conditions.

• Prevents ignition rather than containing it (NEC 504.2).
• Used in hazardous (classified) locations.
• Requires specific design, components, and installation practices.

Memory trick: Intrinsic Safety is 'IN'side and 'SAFE', never letting a 'SPARK' ignite.

Regardless of insulation temperature rating, 14 AWG copper conductors used in general branch circuits are typically limited to a maximum 15-ampere overcurrent protective device.

• NEC 240.4(D) specifies limits.
• Applies to 14 AWG copper.
• Maximum OCPD is 15 A.

Memory trick: Protecting 'wires' from 'too much current' is 'critical'.

GFPE is a system designed to protect equipment and property from damaging ground-fault currents, typically found on larger services, by opening the circuit before extensive damage occurs.

• Required for 480Y/277V, 3-phase, 4-wire services rated 1000A or more.
• Maximum setting for the ground-fault device is 1200A.
• Not intended for personnel protection.

Memory trick: Ground Faults need 'EQ'uipment 'P'rotection, 'E'veryone needs to know the '230.95' rule.

A Ground-Fault Circuit Interrupter (GFCI) for personnel protection is designed to trip when a ground-fault current of 5 milliamperes (±1 mA) or more is detected, preventing electric shock.

• Nominal trip level is 5 mA.
• Protects against electric shock to humans.
• Required in specific locations like bathrooms, kitchens, outdoors.

Memory trick: GFCI is like a '5'-star bodyguard, always sensing a 'leak' to keep you safe.

Ground-fault protection of equipment (GFPE) is required for the essential electrical system in hospitals and must be selectively coordinated with all supply-side overcurrent protective devices to ensure continuity of power.

• NEC 517.17 governs requirements.
• Applies to essential electrical systems.
• Requires selective coordination for GFPE.

Memory trick: Hospital 'essential' systems need 'alert' 'power' protection.

Selective coordination is a system design principle where the overcurrent protective device closest to an overcurrent or fault condition operates first, isolating only the affected circuit and leaving the rest of the electrical system energized.

• Minimizes power outages to specific fault locations.
• Achieved by proper selection and settings of OCPDs.
• Crucial for critical systems like hospitals, data centers.

Memory trick: Coordination is like a 'select'ive 'firewall', keeping problems contained.

Time-delay fuses for motor short-circuit and ground-fault protection are typically sized at 175% of the motor's full-load current (FLA), with the next higher standard size permitted if the calculated value is not standard.

• Base percentage for time-delay fuses is 175% of FLA (NEC Table 430.52).
• Next higher standard size is allowed if calculated value is not standard (NEC 240.6, 430.52 Exception).
• Maximum for time-delay fuses, even with next size rule, is 225% of FLA.

Memory trick: Motor fuses are 'Timed' to perfection, '175' is the magic number, then go 'Next' if needed.

For escalators and moving walks, the NEC allows for higher overcurrent protective device (OCPD) ratings, especially for instantaneous trip breakers (up to 400% or more if listed), to accommodate the high inrush currents of large motors while still ensuring short-circuit protection.

• OCPD for motors per Article 430, but with specific allowances.
• Instantaneous trip breakers can be up to 400% of motor FLA, or more if listed.
• Accommodates high starting currents of escalator motors.
• Ensures short-circuit protection without nuisance tripping.

Memory trick: Escalator Power: Motors surge, so the breaker can be big (400%), but only if it's instant.

Overcurrent protective devices for electric vehicle charging equipment must be sized for not less than 125% of the maximum continuous load.

• Continuous load factor: 125%.
• Applies to EV charging equipment.
• Ensures OCPD can handle prolonged operation without nuisance tripping.

Memory trick: EV Chargers: Just like ovens, they're continuous, so add 25% for safety.

Solar photovoltaic (PV) systems require both AC and DC disconnecting means, readily accessible, to safely isolate the PV array, inverter, and the connection to the premises wiring for maintenance and emergency shutdown.

• Requires separate AC and DC disconnects.
• Both must be readily accessible.
• AC disconnect isolates from utility/premises wiring.
• DC disconnect isolates the array from the inverter.

Memory trick: Solar Power: AC and DC, each needs its own cut-off switch, easy to reach.

The minimum horizontal distance required by the NEC between the edge of a fountain and a general-purpose 125-volt, 15- or 20-ampere receptacle not exclusively for the fountain.

• Prevents electrical hazards near water.
• Applies to general-purpose receptacles.
• NEC Article 680 covers fountains.

Memory trick: Ten feet from the fountain's splash, keep other outlets safe, no clash!

The National Electrical Code (NEC) mandates that fuel cell systems, regardless of being standalone or interconnected, must be grounded in accordance with the general grounding requirements of NEC Article 250 to ensure safety and proper fault protection.

• Grounding per NEC Article 250.
• Applies to DC output circuits and AC output of inverters.
• Ensures fault current path and voltage stabilization.

Memory trick: Fuel Cells: Even if isolated, ground them like everything else, by Article 250.

Electrical installations in agricultural buildings, especially those housing livestock, have specific NEC requirements under Article 547 to address corrosive atmospheres, dust, and damp conditions, often permitting robust wiring methods like Type UF cable.

• Addresses corrosive, damp, and dusty environments.
• Specific wiring methods like Type UF cable are permitted.
• Nonmetallic boxes and enclosures are often preferred.
• Equipment must be listed for the conditions.

Memory trick: Farm Wiring: Corrosive air, so use tough UF cable or non-metal boxes.

For temporary electrical installations, all 125V, single-phase, 15A and 20A receptacles are required to have ground-fault circuit interrupter (GFCI) protection for personnel, ensuring safety on construction sites and similar temporary setups.

• Applies to 125V, 15A & 20A receptacles.
• Mandatory for temporary wiring (NEC 590.6(A)).
• Protects personnel from electrical shock.

Memory trick: Temporary Power: Always GFCI, Always Protected, Always Grounded.

The maximum continuous output current permitted for a single fuel cell inverter output circuit, as specified by the NEC, to ensure safety and proper overcurrent protection coordination.

• Applies to single inverter output circuits.
• NEC Article 692 covers fuel cell systems.
• Helps manage fault currents and protection.

Memory trick: Fuel cell inverter, forty-eight is the max, for safety and code, no relax!

The minimum required separation distance between exposed communication cables and exposed electric light or power conductors (300V or less, not in raceway/cable) as per the NEC.

• Prevents electrical interference and hazards.
• Applies to exposed conductors.
• NEC Article 805 covers communication systems.

Memory trick: Communication and power, exposed and bare, four inches minimum, safety's care!

The required location for the termination of the feeder assembly supplying a manufactured building, as specified by the NEC, to facilitate connection and disconnection.

• Applies to manufactured buildings.
• NEC Article 545 covers this.
• Ensures accessibility for relocation.

Memory trick: Manufactured box, feeder's end, on the exterior wall, a trusty friend!

The National Electrical Code (NEC) specifies that branch circuits supplying signs and outline lighting systems must have a minimum rating of 20 amperes to ensure adequate capacity and safety for these common outdoor electrical installations.

• Minimum 20A branch circuit rating.
• Applies to signs and outline lighting.
• Found in NEC Article 600.

Memory trick: Signs: Minimum 20 amps, just like your kitchen, because they work hard.

Electrical installations at marinas and boatyards, particularly shore power receptacles, have stringent NEC requirements to protect against electric shock hazards in a wet and potentially corrosive environment.

• All shore power receptacles must be GFCI protected.
• Shore power receptacles must be of the locking and grounding type.
• Overcurrent protection and proper grounding are critical.

Memory trick: Marina Power: Lock it, Ground it, GFCI protect it, or a shock might rock it.

The National Electrical Code (NEC) mandates the equipotential bonding of all metal parts associated with a swimming pool to minimize voltage gradients in and around the pool area, preventing dangerous shock hazards.

• All metallic parts of the pool structure, including rebar, must be bonded.
• Bonding conductors for these parts must be solid copper, not smaller than 8 AWG.
• Bonding creates an equipotential plane around the pool.

Memory trick: Pool Safety: Bond All Metal, Ground All Wires, Protect All Swimmers.

The NEC-mandated minimum ampacity for conductors connecting the battery of an Energy Storage System (ESS) to its inverter, based on the continuous output current.

• Continuous current requires 125% sizing.
• NEC Article 706 covers ESS.
• Ensures safe and efficient power transfer.

Memory trick: ESS battery power, one-point-two-five, for conductor's ampacity, keep it alive!

The maximum time permitted by NEC for an emergency lighting system to provide illumination after the failure of the normal power supply.

• Ensures immediate safety during power outages.
• Critical for egress and occupant safety.
• NEC Article 700 covers emergency systems.

Memory trick: Ten seconds to light up the dark, safety's mark!

The minimum continuous ampere rating for the overcurrent protective device required for a 50-ampere, 120/240-volt recreational vehicle site receptacle according to the NEC.

• OCPD must match receptacle rating.
• NEC Article 551 covers RV parks.
• Ensures proper protection for RV connection.

Memory trick: Fifty-amp RV, fifty-amp breaker, for safety's sake, no faker!

The National Electrical Code (NEC) mandates specific minimum clearances for service-drop conductors to mobile homes, requiring at least 10 feet in all directions from the mobile home and its roof area for safety.

• Minimum 10 feet clearance from mobile home.
• Applies to service-drop conductors.
• Ensures safety for occupants and maintenance personnel.

Memory trick: Mobile Home Drop: Ten feet all around, for safety on the ground and up high.

The minimum ampere rating required by the NEC for branch circuits supplying a single X-ray unit in health care facilities, to ensure safe and reliable operation.

• Applies to single X-ray units.
• NEC 517.73(A) governs this.
• Manufacturer's specifications can override the minimum.

Memory trick: X-ray circuits, minimum thirty, for patient safety, don't be dirty!

Specific NEC requirements for wiring methods in agricultural buildings, particularly those with corrosive or damp environments, to ensure safety.

• Corrosive and damp conditions are common.
• Wiring must be protected from physical damage and corrosion.
• Certain wiring methods are explicitly prohibited.

Memory trick: No open wires where the farm dust flies; corrosion's a foe, protect with wise ties!

The minimum size of the equipment grounding conductor for dedicated branch circuits supplying data processing equipment, determined by the circuit's overcurrent protective device rating.

• Follows general EGC sizing rules (NEC 250.122).
• Critical for sensitive electronic equipment.
• Ensures proper fault current path.

Memory trick: Circuit's OCPD sets the EGC's pace, Table 250.122, no guessing case!

In Class I, Division 2 hazardous locations (where flammable gases/vapors are present only under abnormal conditions), the NEC permits specific wiring methods like threaded rigid metal conduit or certain types of metal-clad (MC) cable designed to prevent ignition.

• Flammable gases/vapors present under abnormal conditions.
• Wiring methods prevent ignition from arcs/sparks.
• Permitted methods include RMC, IMC, certain types of MC and MI cable.
• Sealing fittings are crucial where conduits pass from hazardous to nonhazardous areas.

Memory trick: Hazardous Wiring: Division 2 means robust cable or threaded pipe, sealed where it counts.

The NEC mandates specific requirements for the primary power supply of fire alarm systems, including a dedicated, identified branch circuit that is not interrupted by ground-fault or arc-fault protection, to ensure system reliability during emergencies.

• Dedicated branch circuit.
• Permanently identified at supply end.
• No GFCI or AFCI protection allowed.
• Overcurrent protection accessible only to authorized personnel.

Memory trick: Fire Alarm Power: Dedicated, Labeled, and Never GFCI/AFCI.

The required locations for readily accessible disconnecting means for a wind electric system, as mandated by the NEC, to ensure safety during maintenance and emergencies.

• Required at the turbine.
• Required at the point of interconnection.
• Ensures system can be isolated safely.

Memory trick: Wind turbine and cabin connect, two disconnects, for safety, perfect!

The calculation method for determining the minimum overcurrent protective device rating for electric vehicle charging equipment, accounting for continuous load requirements.

• Continuous load requires 125% sizing.
• NEC Article 625 governs EV charging.
• Applies to both residential and commercial installations.

Memory trick: EV charging power, one-point-two-five, for safety's sake, keep it alive!

The minimum required size for a copper supply cord for a 100-ampere mobile home service, as specified by the NEC, to ensure safe and adequate power delivery.

• Specific to mobile home services.
• NEC 550.10(B) governs this.
• Ensures proper ampacity for the service rating.

Memory trick: One hundred amps for the mobile home's hum, No. 2 copper, for power to come!