Journeyman Electrician Exam (NEC) flashcards

In a DC motor, increased resistance in the armature circuit reduces the back electromotive force (EMF) for a given speed, leading to higher armature current but reduced speed under load.

• Motor speed is proportional to (V - I_a*R_a) and inversely proportional to field flux.
• Back EMF (E_b) opposes the applied voltage (V).
• If R_a increases, the voltage drop across R_a increases.
• To maintain torque, current increases, but speed decreases due to reduced effective voltage across the armature.

Memory trick: Speed vs. Current: Back EMF, Resistance, Flux dictate the dance.

Apparent power (kVA) in a 3-phase system is calculated using the line-to-line voltage (V_L) and line current (I_L), and is equal to the product of √3, V_L, and I_L, divided by 1000 to convert to kVA.

• Formula: S = √3 * V_L * I_L
• Units: Volts-Amperes (VA) or kiloVolts-Amperes (kVA).
• Represents the total power flow, including reactive power.
• NEC Table 430.250 provides FLC for motor sizing, not necessarily actual operating current for power calculations.

Memory trick: Real P, Apparent S, Reactive Q; Root-3 for three-phase.

Overcurrent protective devices (OCPDs) for non-continuous loads must have an ampacity not less than 100% of the load served.

• Non-continuous loads operate for less than 3 hours at a time.
• This contrasts with continuous loads, which require OCPDs sized at 125% of the load.
• NEC Articles 210.20(A) for branch circuits and 215.3 for feeders govern OCPD sizing.

Memory trick: OCPD: Continuous 125%, Non-continuous 100%.

NEC Article 430.22(A) mandates that conductors supplying a single motor must have an ampacity of at least 125% of the motor's full-load current rating, before any adjustments or corrections.

• Minimum ampacity = 125% * Motor FLA.
• This factor accounts for motor starting currents and continuous operation.
• Applies to branch-circuit conductors for single motors.
• Further adjustments for temperature or bundling may be required.

Memory trick: Motor conductors need a 25% safety net, for continuous run, don't forget it yet!

NEC Table 220.55 provides demand factors for household electric ranges, cooktops, and ovens to account for their intermittent use in service and feeder calculations.

• For one range over 8.75 kW, the demand load is 8 kW (Column C).
• For ranges 3.5 kW to 8.75 kW, Column A, B, or C may apply depending on quantity.
• These factors prevent oversizing service conductors and overcurrent protection.

Memory trick: Ranges: 220.55, 8kW is the magic number for one big one.

Overcurrent protective devices (OCPDs) for non-continuous loads must be sized at not less than 100% of the load's maximum current rating.

• Calculate load current (I = P/V).
• Non-continuous loads: OCPD ≥ 100% of load current.
• Continuous loads: OCPD ≥ 125% of load current.
• Always use standard OCPD sizes (e.g., 15, 20, 25, 30, 35, 40, 45, 50, 60A).

Memory trick: Calculate, Compare, Choose Standard.

The maximum nominal voltage allowed by the NEC for single-phase branch circuits supplying power to boats at floating docks or marinas.

• Applies to marinas and boatyards (NEC 555).
• Specific to single-phase circuits supplying boats.
• Limited to 250 volts nominal for safety.

Memory trick: Two-fifty is the voltage limit, for a single phase by the water's brim.

Current imbalance in a 3-phase system is the variation in current magnitude between the phases. A small imbalance (typically up to 5-10%) is considered reasonable, while larger imbalances can indicate issues.

• Calculated as (Max Deviation from Avg / Avg Current) * 100%.
• Voltage imbalance is the primary cause of current imbalance.
• High current imbalance can lead to motor overheating and premature failure.
• NEC recommends limiting voltage imbalance to 5%.

Memory trick: Current balance: Check the average, then the deviation.

NEC Article 220.54 specifies how to calculate the demand load for electric clothes dryers in service and feeder calculations.

• The demand load is 5000 W (5 kW) or the nameplate rating, whichever is larger, for each dryer.
• Demand factors apply if there are 4 or more dryers.
• This accounts for intermittent use and prevents oversizing.

Memory trick: Dryer: 5kW or Nameplate, pick the bigger one.

Emergency lighting systems in places of assembly must be capable of automatically maintaining illumination for a minimum of 90 minutes upon loss of normal power.

• Applies to places of assembly (NEC Article 700).
• Ensures safe egress for occupants.
• Minimum duration is 1.5 hours.

Memory trick: Emergency lights: Enough time for ALL to exit safely.

Standardized graphical representations used on electrical drawings to convey information about devices, wiring, and components.

• Symbols provide a universal language for electricians and engineers.
• A legend on each blueprint clarifies specific symbols used in that drawing set.
• Common categories include outlets, switches, lighting, panelboards, and wiring paths.

Memory trick: Hidden Walls, Dashed Lines with Crosses.

The actual voltage available at a load is the supply voltage minus the voltage drop that occurs along the circuit conductors.

• Voltage drop reduces the voltage supplied to the load.
• Excessive voltage drop can impair equipment performance and efficiency.
• VD is often expressed as a percentage of the supply voltage.
• V_load = V_supply - V_drop.

Memory trick: Drop means less; supply minus drop is load.

The minimum insulation temperature rating required by the NEC for power-limited fire alarm (PLFA) circuit conductors to ensure their operational integrity.

• Applies to Power-Limited Fire Alarm (PLFA) circuits (NEC 760).
• Ensures conductor performance during operation.
• Minimum 75°C (167°F) insulation rating.

Memory trick: Seventy-five degrees, for fire alarm wires, that's what the NEC requires.

The determination of the minimum cross-sectional area for the equipment grounding conductor in a photovoltaic system based on the rating of the associated overcurrent protective device, as per NEC Table 250.122.

• Based on the overcurrent protective device rating.
• Ensures safe fault current path.
• Refer to NEC Table 250.122 for sizing.

Memory trick: Grounding conductor size: OCPD rating is the guide, Table 250.122 is where to confide.

Real power (kW) is the actual power consumed by a load that performs useful work, derived by multiplying the apparent power (kVA) by the power factor (PF).

• Real power (P) is measured in watts (W) or kilowatts (kW).
• Apparent power (S) is measured in volt-amperes (VA) or kilovolt-amperes (kVA).
• Power factor (PF) is the ratio of real power to apparent power (PF = P/S).
• PF indicates the efficiency of power utilization; a lower PF means higher reactive power.

Memory trick: P = S x PF, like 'P'eanut 'S'auce 'P'rovider 'F'actory.

Ohm's Law states that the current through a conductor between two points is directly proportional to the voltage across the two points and inversely proportional to the resistance between them. For resistance, it's V/I.

• R = V / I
• Units: Volts (V), Amperes (A), Ohms (Ω)
• Fundamental to DC and AC circuit analysis

Memory trick: VIR: Voltage Is Resistance times Current. For Resistance, cover R and you get V over I.

A universal motor is a series-wound motor that can operate on both AC and DC power, featuring brushes and a commutator, high starting torque, and variable speed.

• Operates on AC or DC.
• Contains brushes and a commutator.
• High starting torque.
• Speed decreases with increasing load.

Memory trick: Universal motors use brushes and a commutator, so they can power tools and vacuum cleaners with great fervor.

Root Mean Square (RMS) values for AC voltage and current represent the effective value that would produce the same heating effect as a DC equivalent. For sinusoidal waveforms, RMS = Peak / √2.

• RMS = Peak / √2 (for sine wave).
• Peak = RMS * √2 (for sine wave).
• Most AC meters display RMS values.
• RMS is used for power calculations (P = V_rms * I_rms).

Memory trick: RMS is the 'real' power, peak is the 'pointy' power. Divide by root 2 to get real from pointy.

Equipment grounding conductors for swimming pool motors must be a minimum of 12 AWG copper, regardless of the overcurrent protective device size, as per NEC Article 680.

• Specific requirement for pool motors (NEC 680.21(A)(4)).
• Overrides general EGC sizing rules (NEC 250.122).
• Applies to all pool pump motors for enhanced safety.

Memory trick: Pool motors: 'Twelve' gauge for ground, always safe around water.

Ohm's Law for Power relates power (P), voltage (V), and current (I) in an electrical circuit.

• P = V × I (Power = Voltage × Current)
• P = I² × R (Power = Current squared × Resistance)
• P = V² / R (Power = Voltage squared / Resistance)

Memory trick: P-IV, Power is IV, as in intravenous, a direct line.

The minimum vertical distance required by the NEC for open conductors of temporary installations above areas accessible only to pedestrians.

• Applies to temporary installations (NEC 590).
• Specific to open conductors over pedestrian areas.
• Minimum 3.0 m (10 ft) clearance.

Memory trick: Ten feet high, for walkers passing by, temporary wires in the sky.

For balanced 3-phase loads, the total current on each phase of a feeder is the arithmetic sum of the individual phase currents of the connected loads.

• Assumes balanced loads, where each phase draws approximately the same current.
• Diversity factors are often applied in real-world scenarios but are excluded here.
• This principle applies to the current on each individual phase conductor.

Memory trick: Balanced 3-Phase: Just add 'em up, like a shopping list.

Resistivity is an intrinsic property of a material that quantifies how strongly it resists electrical current. Copper has lower resistivity than aluminum.

• Lower resistivity means better conductivity.
• Copper is a better conductor than aluminum.
• Resistance is directly proportional to resistivity, length, and inversely proportional to cross-sectional area.

Memory trick: CoPPer is a better Conductor than AlumiNum.

Apparent power (S) in a 3-phase system is the product of the line voltage, line current, and the square root of 3. It is measured in Volt-Amperes (VA).

• S = √3 * V_line * I_line
• Includes both real and reactive power components.
• Used for sizing electrical equipment like transformers and generators.

Memory trick: Three-phase power, 'Root Three VI' for apparent, 'Root Three VI Cosine' for real.

The maximum permissible time for an emergency power system to activate and supply power to critical loads in a healthcare facility after the normal power supply fails.

• Applies to emergency systems in healthcare facilities.
• Ensures continuous operation of life-safety and critical equipment.
• Mandated by NEC to be within 10 seconds.

Memory trick: Ten seconds to save lives in a hospital emergency.

Power-limited fire alarm (PLFA) circuit conductors must maintain a minimum 0.25-inch separation or use a barrier when run with Class 1, NPLFA, or medium-power network-powered broadband communications circuits within the same raceway.

• Applies to PLFA circuits (NEC Article 760).
• Prevents electrical interference and ensures reliability.
• Separation is 0.25 inches without a barrier.

Memory trick: Fire alarm wires: Keep 'Quarter-inch' apart for clear signals.

Voltage drop is the reduction in electrical potential along the length of a conductor due to its resistance, calculated to ensure proper appliance operation.

• VD = (2 × K × I × L) / CM for single-phase circuits (K is conductor constant).
• Maximum allowable voltage drop is typically 3% for branch circuits and 5% for feeder + branch circuits combined.
• Larger conductor sizes (smaller AWG number) reduce voltage drop.

Memory trick: VD: Very Distant wires need Very Durable (Large) conductors.

Power dissipation refers to the rate at which electrical energy is converted into heat or other forms of energy within a circuit component.

• P = V² / R (Power = Voltage squared / Resistance)
• P = I² × R (Power = Current squared × Resistance)
• P = V × I (Power = Voltage × Current)
• Measured in Watts (W).

Memory trick: P = V I R² - Power is V-I-R-squared, like VIRUS but with R².

The maximum permissible time for an emergency power system to activate and supply power to designated loads after the normal power supply fails, as per NEC Article 700.

• Applies to general emergency systems (e.g., places of assembly).
• Ensures essential services during power outages.
• Mandated by NEC to be within 10 seconds.

Memory trick: Ten seconds is the time, for emergency power to shine.

In a standard 3-wire delta electrical system, there is no inherent neutral conductor, and therefore no phase-to-neutral voltage available.

• Phase-to-phase voltage is present.
• No neutral point is typically derived without additional equipment (e.g., grounding transformer).
• Used primarily for 3-phase motor loads.

Memory trick: Delta has no 'N'eutral, Wye has 'Y'our neutral.

Conductors supplying continuous loads (operating for 3 hours or more) must be sized to have an ampacity of not less than 125% of the continuous load current.

• Applies to feeders and branch circuits.
• NEC 210.19(A)(1) for branch circuits, 215.2(A)(1) for feeders.
• This factor prevents overheating of conductors under prolonged operation.

Memory trick: For continuous current, conductors need 125% more flow capacity.

In a three-phase system, apparent power (S) is the total power that appears to be consumed by the load, including both real and reactive power, calculated using line-to-line voltage and line current.

• Formula: S = √3 × V_line × I_line.
• Expressed in Volt-Amperes (VA) or kiloVolt-Amperes (kVA).
• Used for sizing transformers, generators, and OCPDs.

Memory trick: Root 3 for Line values, P for Real, S for Apparent, Q for Reactive.

The electrical blueprint symbol for a special purpose outlet is a circle with two diagonal lines forming an 'X' inside it, often accompanied by text indicating its specific use or voltage.

• Used for dedicated equipment or specific voltage/current requirements.
• Distinguished from general-purpose receptacles.
• Standardized by ANSI/IEEE for clarity in drawings.
• Variations exist, but the 'X' within a circle is common.

Memory trick: X marks the 'Special' spot for outlets.

The minimum temperature rating required for DC PV source circuit and PV output circuit conductors, typically 90°C wet-rated, to withstand high temperatures and environmental conditions.

• Applies to PV source and output circuit conductors (NEC 690).
• Accounts for high ambient temperatures (e.g., attics, rooftops).
• Minimum 90°C wet-rated conductors are generally required.

Memory trick: Ninety degrees is the hot rule, for PV wires, don't be a fool.

A 3-phase Wye (star) electrical distribution system provides both phase-to-phase and phase-to-neutral voltages.

• Phase-to-phase voltage (V_LL) = √3 × Phase-to-neutral voltage (V_LN).
• Phase-to-neutral voltage (V_LN) = V_LL / √3.
• Common Wye systems are 208Y/120V and 480Y/277V.

Memory trick: Y-system: Your hot-to-hot is bigger by root 3.

An enclosure designed to contain any internal explosion of a hazardous atmosphere and prevent the ignition of the external atmosphere through its joints or by excessive surface temperature.

• Withstands internal explosions.
• Prevents spread of explosion to external atmosphere.
• Limits external surface temperature.
• Required in Class I, Division 1 locations.

Memory trick: Explosionproof: Keep the boom inside, so the outside won't ignite.

Overcurrent protective devices (OCPDs) for branch circuits serving patient care areas in healthcare facilities must be specifically identified as suitable for this critical application.

• Applies to patient care areas (e.g., operating rooms, patient rooms).
• Ensures enhanced safety and reliability.
• NEC 517.16 is the governing article.

Memory trick: Healthcare OCPDs: Always IDENTIFIED, never just generalized.

According to Kirchhoff's Current Law (KCL), the total current entering a junction (or leaving the source) in a parallel circuit is equal to the sum of the currents flowing through each branch.

• Voltage is the same across all parallel branches.
• Current divides among the branches.
• Total resistance in parallel is less than the smallest individual resistance.
• KCL is fundamental to parallel circuit analysis.

Memory trick: Parallel paths, current adds, voltage stays.

Temporary overhead feeder and branch circuit conductors must maintain specific vertical clearances above grade, varying by the area beneath them, to ensure safety on construction sites.

• Applies to temporary installations (NEC Article 590).
• Clearance depends on the area (e.g., pedestrian, vehicle traffic).
• Ensures safety from accidental contact.

Memory trick: Temporary wires: Keep a CLEAR path, especially for people and trucks.

A standardized graphic representation on electrical blueprints indicating the location and type of a single-pole switch.

• A circle with an 'S' and a diagonal line is common.
• Used to control a light or device from one location.
• Essential for interpreting wiring diagrams.

Memory trick: Switches are S-circled, outlets are lines, lights are plain circles.

The minimum size of the Grounding Electrode Conductor (GEC) is determined by the size of the largest ungrounded service entrance conductor, as specified in NEC Table 250.66.

• GEC protects against lightning, surges, and stabilizes voltage.
• Size depends on the ampacity of the service conductors.
• Table 250.66 is the primary reference for GEC sizing.
• Different columns for copper and aluminum GECs.

Memory trick: GEC size links to Service wire, through Table 250.66.

The NEC requirement for how X-ray equipment in health care facilities must be supplied by electrical circuits to ensure safe and reliable operation.

• Applies to X-ray equipment in health care facilities (NEC 517).
• Requires a separate branch circuit.
• Prevents interference with other equipment.

Memory trick: X-ray machine, a single circuit is keen, keeping it clean.

In a series circuit, components are connected end-to-end, so the current is the same through each component, and voltages add up.

• Total Resistance (R_total) = R1 + R2 + R3 + ...
• Current (I) is constant throughout the circuit.
• Total Voltage (V_total) = V1 + V2 + V3 + ... (Kirchhoff's Voltage Law).

Memory trick: Series: Current's the same, Resistance sums up, Voltages drop.

The National Electrical Code (NEC) provides specific demand factors in Article 220, Part III (Table 220.56) for calculating the feeder and service loads of commercial cooking equipment, acknowledging their diverse and intermittent use.

• Reduces the calculated load for multiple appliances.
• Prevents oversizing of electrical infrastructure.
• Based on the number of units and their ratings.
• Crucial for cost-effective and safe design of commercial kitchens.

Memory trick: General, Optional, or Specific Demand.

A specific type of receptacle, identified by a green dot, mandated by the NEC for use in patient care areas where patients are subject to involuntary movement due to their enhanced durability and grounding reliability.

• Required in patient care areas (NEC 517).
• Specifically for areas with involuntary patient movement.
• Identified by a green dot on the face.

Memory trick: Green dot for the patient's spot, especially when they cannot stop.

Conductors supplying continuous loads (expected to operate for 3 hours or more) must be sized to carry at least 125% of the continuous load current.

• NEC 210.19(A)(1) for branch circuits and 215.2(A)(1) for feeders.
• This factor accounts for heat buildup over extended operation.
• The overcurrent protective device must also be sized for 125% of the continuous load.

Memory trick: Continuous: 125% for safety, then check the table.

Incandescent lamps draw a momentary high current (inrush current) upon energization due to the low resistance of their cold filament, which can be significantly higher than their steady-state operating current.

• Cold filament resistance is much lower than hot filament resistance.
• Inrush current can be 10-15 times the normal operating current.
• Lasts for a very short duration (milliseconds).
• Can cause nuisance tripping of overcurrent protective devices.

Memory trick: Overload, Short, Ground, or Inrush Surge.

Real power (P) in a single-phase AC circuit is the actual power consumed by the load and converted into useful work or heat, measured in Watts (W).

• Formula: P = V × I × PF, where V is voltage, I is current, and PF is power factor.
• Also known as active power or true power.
• Always less than or equal to apparent power (S).

Memory trick: P.I.F. – Power Is Fun, with PF.

The ratio of the voltage drop across a circuit or conductor to the source voltage, expressed as a percentage. It indicates how much voltage is lost due to resistance.

• Calculated as (Voltage Drop / Source Voltage) * 100%.
• Excessive voltage drop can cause poor appliance performance and increased current.
• NEC recommends a maximum of 3% voltage drop for feeders and branch circuits.

Memory trick: Drop over Source, then multiply to Percent.

The minimum vertical distance from the ground or operating surface to the operating handles of overcurrent protective devices in temporary installations when accessible to the public.

• Applies to temporary installations (NEC 590).
• Prevents public tampering with OCPDs.
• Mandated at 1.8 m (6 ft) minimum.

Memory trick: Six feet high keeps the public eye off the temporary power's control.

Techniques used to prevent ignition of flammable atmospheres by electrical equipment in hazardous (classified) locations, as defined by NEC Article 500.

• Methods vary by Class, Division, and Zone.
• Aims to contain explosions, prevent ignition, or limit energy.
• Examples: explosionproof, purged/pressurized, intrinsic safety.

Memory trick: Class I Division 2, keep the fumes out, pressurize through and through.

The specific type of ground-fault circuit interrupter required for 125-volt, 15- or 20-ampere receptacles located near swimming pools to ensure personnel protection.

• Applies to receptacles within 2.0 m (6.5 ft) of pool walls (NEC 680).
• Protects against electric shock to personnel.
• Class A GFCI (5 mA trip) is required.

Memory trick: Close to the pool, Class A is the rule, keeping shocks at bay, that's really cool.

Terminals for overcurrent protective devices and disconnects in PV systems often require a minimum temperature rating of 90°C to accommodate conductor ampacities derived from the 90°C column and withstand typical PV operating temperatures.

• Applies to PV source and output circuits.
• Related to conductor ampacity calculations (90°C column).
• Addresses elevated temperatures in PV installations.

Memory trick: PV terminals: 'Ninety' degrees, for the sun's hot embrace.

The minimum length of conductor required to extend from an outlet box, junction box, or switch box to allow for proper splicing or connection of devices or luminaires.

• NEC 300.14 specifies 150 mm (6 inches).
• Ensures adequate room for making safe and reliable connections.
• Applies to all conductors entering the box.

Memory trick: Box Wires: Six Inches, No Less Than That.

The grounding electrode conductor connected to a metal underground water pipe electrode must be sized according to NEC Table 250.66, based on the size of the service-entrance conductors.

• Applies to metal underground water pipe electrode.
• Sized from NEC Table 250.66.
• Based on the largest ungrounded service-entrance conductor size.

Memory trick: Water pipe GEC: Service conductor's call!

The main bonding jumper (MBJ) size is determined by the size of the largest ungrounded service-entrance conductors, as per NEC® Table 250.102(C)(1).

• Connects the equipment grounding conductor to the grounded service conductor and service enclosure.
• Sized based on ungrounded service-entrance conductors.
• Refer to NEC® Table 250.102(C)(1).

Memory trick: MBJ links to the service's biggest wire, like a big brother.

The maximum current that a branch circuit can carry continuously (3 hours or more) without exceeding 80% of the circuit's overcurrent device rating, as required by the NEC.

• NEC 210.23(A)(1) and 210.20(A) specify the 80% rule.
• Applies to most branch circuits with continuous loads.
• Protects against excessive heat buildup in conductors and devices.

Memory trick: Branch Circuit: Continuous Load, Eighty Percent Safe.

The overcurrent protective device for the conductors of a motor control circuit, sized according to NEC 430.72, to protect against overcurrents specific to control wiring.

• NEC 430.72(B) and Table 430.72(B) govern sizing.
• Conductor size dictates maximum OCPD rating.
• Different rules apply if derived from the motor branch circuit vs. separate source.

Memory trick: Control Wire: Size Conductor, Check Table, Pick Max.

For sizing conductors, overcurrent protection, and disconnects for motors, the NEC requires using full-load current values from Article 430 tables, not the motor's nameplate FLA.

• NEC 430.6(A)(1) mandates using table values.
• Tables account for worst-case conditions and design factors.
• Nameplate FLA is for motor overload protection only.

Memory trick: Motor Sizing: Table Trumps Tag for True Current.

Overcurrent protection for motor branch circuits designed to protect the motor circuit components (conductors, control apparatus) from short circuits and ground faults.

• Sized based on NEC Table FLA, not nameplate FLA.
• Multipliers from NEC Table 430.52(C)(1) are used.
• Maximum ratings can be increased if the motor fails to start, up to specific limits.

Memory trick: Motor Fuse: Table FLA, Max Multiplier, Then Standard Size.