NASCLA Journeyman Electrician cheat sheet

Ohm's law: E = I × R; power P = E × I = I²R = E²/R for resistive circuits.

Series circuit: same current, voltages add, R_T = R1 + R2 + ...; parallel circuit: same voltage, currents add, 1/R_T = Σ(1/R).

Balanced three-phase power: P = √3 × V_L × I_L × power factor.

Voltage drop: single-phase 2KID/CM; three-phase √3KID/CM, where K is the conductor constant.

Continuous load: expected to operate 3 hours or more; branch-circuit OCPD and conductors are sized at 125% of continuous current plus noncontinuous load.

NEC Article 100 contains definitions; Article 110 contains general requirements; Article 90 covers scope and enforcement.

Ampacity adjustment: apply ambient-temperature correction and conductor-count adjustment from NEC 310.15; use the lower adjusted ampacity.

RMS sine wave: V_RMS = 0.707 × V_peak; V_peak = 1.414 × V_RMS.

Service disconnecting means must be grouped, marked, and have no more than six switches or breakers to disconnect all service conductors.

Service-entrance conductors are sized per Article 230 and the ampacity tables; the service load is calculated per Article 220.

Dwelling receptacle spacing: wall space must be arranged so no point is more than 6 ft from a receptacle; receptacles are generally no more than 12 ft apart.

Dwelling small-appliance branch circuits: at least two 20A circuits for kitchen countertop; laundry and bathroom require dedicated 20A circuits.

GFCI protection is required in dwelling bathrooms, garages, outdoors, kitchens, laundry, crawl spaces, and unfinished basements per 210.8.

Branch-circuit OCPD for continuous loads: 125% continuous plus 100% noncontinuous load, then select a standard rating.

Feeder and branch-circuit conductors must have ampacity at least equal to the load; the OCPD protects conductors per 240.4.

Raceway fill: 53% for one conductor, 31% for two, 40% for three or more; a nipple may be filled to 60% of cross-sectional area.

EMT must be secured within 3 ft of boxes and supported at intervals not exceeding 10 ft.

Paralleled conductors: minimum 1/0 AWG, same material, size, insulation, length, and terminations.

NM cable is prohibited in wet locations and where subject to physical damage; use raceway or approved cable where required.

Equipment grounding conductor is sized from Table 250.122 based on the rating of the overcurrent device.

Conductors in wet locations require moisture-resistant insulation and approved fittings; splices in wet locations require listed connectors.

Conductor ampacity comes from Table 310.16; derate for ambient temperature and number of current-carrying conductors.

Copper branch-circuit conductors: 14 AWG for 15A, 12 AWG for 20A, and 10 AWG for 30A are common minimum sizes per Table 310.16.

Box fill volume: 14 AWG = 2.00 in³, 12 AWG = 2.25 in³, 10 AWG = 2.50 in³ per conductor; add clamps, devices, and EGC as specified.

All equipment grounding conductors in a box count as one conductor for box fill.

Each yoke or device counts as two conductors of the largest conductor connected to it for box fill.

Boxes must be accessible without removing building finish; boxes may not be buried.

Receptacles in wet or damp locations require weather-resistant types and GFCI protection where required.

A 15A receptacle is permitted on a 20A circuit only where the circuit supplies two or more receptacles per 210.21(B)(3).

Switches and receptacles must be installed in boxes; faceplates are required, and device grounding terminals are bonded to the EGC.

Cable clamps count as one conductor for box fill.

Grounding electrode system: rod, pipe, plate, concrete-encased electrode, or ground ring; if one rod has more than 25 ohms, add a second electrode per 250.53.

GEC is sized per Table 250.66; EGC is sized per Table 250.122; the main bonding jumper bonds the grounded service conductor to the EGC bus.

Separately derived system: bond X0 to the transformer enclosure and grounding electrode; install the system bonding jumper.

NEC 240.4(B) permits the next higher standard OCPD for certain circuits ≤800A when conductor ampacity does not match a standard rating and the load is not a multioutlet receptacle circuit.

GFCI protects people from ground-fault current; AFCI detects arcing faults; neither replaces overcurrent protection.

Bonding connects metal parts to ensure a fault-current path; grounding connects the electrical system to earth.

An overcurrent device interrupts overloads and short circuits and must be rated for voltage and available fault current.

The grounding electrode conductor must be continuous and installed without splices except as permitted by Article 250.

Motor branch-circuit conductors: at least 125% of motor full-load current from Tables 430.248–430.250 for continuous-duty motors.

Motor overload protection: typically 115% to 125% of nameplate FLA, depending on service factor and temperature rise.

Short-circuit and ground-fault protection for motors is sized per Table 430.52; it may be increased if starting current trips the device.

Motor disconnecting means must be within sight of the motor and controller, readily accessible, and lockable where required.

Motor controller must have a horsepower rating not less than the motor horsepower.

HVAC hermetic compressor branch circuits use nameplate rated-load amps and Article 440 rules.

Thermal overload relays protect motor windings from sustained overload; they do not protect the branch circuit from short circuits.

Motor full-load current for conductor sizing comes from NEC tables, not the motor nameplate current.

Single-phase transformer kVA = V × I / 1000; three-phase kVA = √3 × V_L × I_L / 1000.

Transformer overcurrent protection is per Table 450.3(B); primary and secondary OCPD ratings depend on transformer voltage and current.

Separately derived transformer: bond secondary X0 to the enclosure, install the system bonding jumper, and connect to the grounding electrode.

Transformer secondary conductors are protected by OCPD; tap rules in 240.21(C) allow limited lengths without secondary OCPD.

Dry-type transformers require listed clearances and ventilation; access and working space follow Article 110.

Transformer nameplate primary and secondary currents are used to size conductors and overcurrent protection; conductors must have ampacity at least equal to the load.

A delta-wye transformer provides a grounded neutral on the secondary; a delta-delta transformer may be ungrounded.

Available fault current at a transformer secondary depends on kVA and impedance; equipment must have adequate SCCR.

Hazardous location classes: Class I flammable gases or vapors; Class II combustible dust; Class III ignitable fibers or flyings.

Division 1 means the hazard is present under normal conditions; Division 2 means the hazard is present only under abnormal conditions.

Hazardous-location equipment must be marked with class, division, and group; use listed fittings and seals as required.

Dwelling bathroom receptacles require GFCI protection; at least one receptacle must be within 3 ft of each basin.

Swimming pool areas require equipotential bonding of metal parts and specified clearances for receptacles; GFCI protection is required.

Wet locations require weather-resistant receptacles and enclosures; all openings must be closed.

Special equipment such as signs, welders, and elevators has additional requirements in Articles 600, 630, and 620.

Temporary wiring on construction sites is subject to Article 590 and GFCI requirements.

Lockout/tagout: isolate all energy sources, apply locks and tags, release stored energy, and verify zero energy before work.

OSHA 29 CFR 1926 Subpart K covers construction electrical safety; GFCI protection is required for 15A and 20A, 120V receptacles on construction sites.

Arc-flash PPE and approach boundaries are based on incident energy and voltage; only qualified persons may enter the restricted approach boundary.

Test before touch: verify the circuit is de-energized with a meter rated for the category and voltage.

Extension cords must be three-wire with grounding, not daisy-chained, and free of damage; use GFCI where required.

Ladders: extend 3 ft above the landing, set at a 4:1 slope, and maintain three-point contact.

Voltage-rated gloves require inspection and testing per class; leather protectors are used over rubber gloves.

Dwelling general lighting load: 3 VA per square foot; small-appliance circuits add 1500 VA each; laundry adds 1500 VA.

Dwelling demand factor: first 3000 VA at 100%; remaining general lighting and appliance load at 35% per 220.42.

Service load calculation sums general lighting, small-appliance, laundry, appliance, HVAC, and motor loads, then applies demand factors.

Voltage drop formula: single-phase 2KID/CM; three-phase √3KID/CM, where K is the resistivity constant.

Plan scale: 1/4 inch = 1 foot means 1/4 inch on the drawing represents 12 inches actual.

Panel schedule shows circuit numbers, breaker ratings, loads, and phase balance; verify neutral and grounding bars.

Box fill calculation: count conductors and fittings, multiply by Table 314.16(B) volume, and compare with box volume.

Feeder and service conductor size is selected from ampacity tables after load calculation and adjustment factors.