Journeyman Electrician Exam (NEC)

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.

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.

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.

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.

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.

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.

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 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.

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.

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.

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.

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.

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.

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).

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

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.

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.

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.

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)

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.

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.

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.

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.

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.