NCCER Electrical cheat sheet

Treat all conductors as energized until tested with a voltage tester rated for the circuit; test the tester before and after the check.

Lockout/tagout sequence: notify, shut down, isolate, lock and tag, release stored energy, and verify absence of voltage at the point of work.

A Class A GFCI trips at 4–6 mA of current imbalance and is used for personnel protection in locations specified by NEC 210.8.

Arc-rated PPE must meet or exceed the calculated incident energy; 1.2 cal/cm² is commonly used as the second-degree-burn threshold.

Rubber insulating glove classes: Class 00 ≤500 V, Class 0 ≤1,000 V, Class 1 ≤7,500 V, Class 2 ≤17,000 V.

Body current effects: about 1 mA perception, 10–15 mA let-go threshold, 30 mA respiratory tetany, and 50–100 mA ventricular fibrillation.

Only qualified persons may cross the restricted approach boundary, and doing so requires an energized work permit and appropriate PPE.

Temporary receptacles on construction sites require GFCI protection.

Ohm's law: V = I × R; rearrange to I = V/R or R = V/I for resistive circuit calculations.

Power formulas: P = V × I = I²R = V²/R for DC and resistive AC loads.

Series circuit: current is constant, resistances add, and voltage divides in proportion to resistance.

Parallel circuit: voltage is constant across branches, branch currents add, and total resistance is less than the smallest branch resistance.

Capacitive current leads voltage by 90°, while inductive current lags voltage by 90° in a pure AC circuit.

Power factor = real power / apparent power = cos θ for sinusoidal waveforms.

Balanced three-phase real power: P = √3 × line voltage × line current × power factor.

RMS value of a sine wave = 0.707 × peak value; peak value = 1.414 × RMS.

Kirchhoff's current law: current entering a junction equals current leaving; Kirchhoff's voltage law: voltages around a closed loop sum to zero.

Continuous loads require branch-circuit conductors and overcurrent devices sized at not less than 125% of the continuous load before adjustments.

A standard overcurrent device may carry only 80% of its rating continuously unless it is listed for 100% operation.

Ampacity adjustment for bundled current-carrying conductors: 80% for 4–6, 70% for 7–9, and 50% for 10–20 conductors.

Ambient temperature correction factors are based on a 30°C (86°F) ambient; higher ambient reduces conductor ampacity.

Informational notes recommend no more than 3% voltage drop on a branch circuit and 5% total from the service to the farthest outlet.

Box fill is calculated by summing conductor, device, fitting, and equipment-grounding volumes and comparing the total with the box volume from NEC 314.16.

Working space for energized equipment: at least 30 in wide, 36 in deep for 0–150 V to ground, and 6.5 ft high.

Dwelling-unit receptacle spacing: no point along the floor line may be more than 6 ft from an outlet, and wall spaces 2 ft or wider require an outlet.

GFCI protection requirements are in NEC 210.8; AFCI protection requirements are in NEC 210.12.

No more than 360° of total bends is permitted between pull points in a raceway run.

EMT must be supported within 3 ft of each box or fitting and at intervals not exceeding 10 ft.

Rigid metal conduit and intermediate metal conduit must be supported within 3 ft of each box and at intervals not exceeding 10 ft.

Maximum raceway fill: 53% for one conductor, 31% for two conductors, and 40% for three or more conductors.

Liquidtight flexible metal conduit must be supported within 12 in of each box and at intervals not exceeding 4.5 ft.

Bushings are required where conductors 4 AWG and larger enter a box or enclosure through a raceway.

Expansion fittings are required where raceway runs are subject to expansion or contraction, such as long PVC runs.

Raceway bends must not damage conductors; the minimum bend radius depends on raceway type and size.

Where a raceway terminates at a box, the raceway and box must be securely fastened and mechanically connected.

Copper conductor overcurrent protection: 14 AWG is generally limited to 15 A, 12 AWG to 20 A, and 10 AWG to 30 A.

Ampacity tables have 60°C, 75°C, and 90°C columns; the usable ampacity is limited by the lowest temperature rating of the conductor and its terminations.

Grounded conductors are identified by white or gray, or by three continuous white stripes on other than green insulation.

Equipment grounding conductors are identified by green, green with yellow stripes, or bare metal.

The neutral counts as a current-carrying conductor where it carries unbalanced current, but not in a balanced three-phase wye feeder.

THHN is a 90°C dry-location insulation with a nylon jacket; in wet locations its ampacity is limited to the 75°C column.

Splices must be made in accessible enclosures such as boxes or conduit bodies, not buried in walls or raceways.

Voltage drop approximates: VD = 2 × K × I × L / CM for single-phase, using conductor constant K and circular mils.

NM cable must be supported at intervals not exceeding 4.5 ft and within 12 in of each box.

The grounding electrode conductor is sized from NEC Table 250.66 based on the largest ungrounded service conductor.

The equipment grounding conductor is sized from NEC Table 250.122 based on the rating of the circuit overcurrent device.

A single rod, pipe, or plate electrode must have 25 ohms or less resistance to earth, or a second electrode must be installed.

The main bonding jumper connects the grounded service conductor to the service equipment enclosure and the equipment grounding conductor at the service.

Motor branch-circuit conductors must have an ampacity of at least 125% of the motor full-load current from the Article 430 tables.

Motor overload protection is generally set at 125% of nameplate current for a service factor of 1.15 or higher, and 115% otherwise.

Motor short-circuit and ground-fault protection generally follows NEC 430.52: 250% for an inverse-time breaker, 175% for a dual-element fuse, and 300% for a non-time-delay fuse.

A motor disconnecting means must be within sight of the motor and controller or capable of being locked open.

Two-wire control uses a maintained-contact switch; three-wire control uses momentary start/stop pushbuttons with a holding contact and undervoltage release.