Master Electrician cheat sheet

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

AC impedance: Z = √(R² + (X_L − X_C)²); X_L = 2πfL; X_C = 1/(2πfC).

Balanced three-phase real power: P = √3 × V_L × I_L × PF; reactive power Q = √3 × V_L × I_L × sin θ.

Sine wave: RMS = peak ÷ √2; peak = RMS × 1.414; full-cycle average of a pure sine is zero.

Voltage drop: single-phase VD ≈ 2KIL/CM; three-phase VD ≈ 1.732KIL/CM, where K is conductor resistivity constant.

Continuous load: operates at maximum current for 3 hours or more; size conductors and OCPDs at 125% where required.

Ampacity depends on conductor size, insulation temperature rating, ambient temperature, and number of current-carrying conductors.

Grounded conductor is the neutral or circuit conductor intentionally connected to earth; grounding conductor is the equipment grounding conductor.

Raceway fill: 1 conductor 53%, 2 conductors 31%, 3 or more 40%; nipples 60% for 3 or more.

Box fill: 14 AWG = 2.0 in³, 12 AWG = 2.25 in³, 10 AWG = 2.5 in³; count each conductor, clamp, device, and ground.

NM cable support: within 12 in of box and every 4.5 ft; secure where required and protect from physical damage.

EMT support: within 3 ft of box and every 10 ft; RMC support every 10 ft; IMC similar to RMC.

Expansion fittings are required where raceway crosses building expansion joints or where thermal movement is expected.

Bushings are required where conductors 4 AWG and larger enter a raceway or box, to protect insulation.

Metal raceways and cables must be bonded and grounded; using raceway as EGC requires compliant continuity and fittings.

Direct-buried cable minimum cover depends on voltage and location; NEC Table 300.5 sets depths such as 24 in for general direct burial.

Dwelling general lighting: 3 VA/ft²; small-appliance circuits: two or more 20A, 1500 VA each; laundry: 1500 VA.

Bathroom receptacle circuits must be 20A and may serve only bathroom outlets; kitchen counter receptacles need GFCI.

Continuous branch-circuit load: conductor and OCPD sized at 125% of continuous load plus 100% of noncontinuous load.

Non-dwelling receptacle load: 180 VA per yoke; dwelling receptacle outlets are included in general lighting unless specific.

Standard OCPD ratings: 15, 20, 25, 30, 40, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200 A.

Dwelling lighting demand: first 3000 VA at 100%, remaining general lighting at 35%; appliance demand factors apply separately.

Fixed electric space heating: branch circuit and OCPD sized at 125% of nameplate load.

Multiwire branch circuit: line-to-neutral loads; handle-tied breaker or simultaneous disconnect required.

OCPD must protect conductors at their ampacity; next higher standard rating permitted only where ampacity does not match a standard size and conditions are met.

Interrupting rating must be at least available fault current; series ratings require a listed combination.

Motor branch: overload protects motor; short-circuit/ground-fault device protects conductors; conductor ≥125% FLC.

Tap rule: 10-ft tap and 25-ft tap require specific ampacity, length, and enclosure conditions.

GFPE for 480Y/277V service disconnects 1000A or more: maximum 1200A setting with time delay for selectivity.

Selective coordination required for emergency systems, legally required standby, and critical operations power systems.

Ambient temperature and conductor bundling derating reduce ampacity before selecting OCPD.

Current-limiting devices reduce let-through energy but do not by themselves ensure coordination.

Service grounded conductor bonded to grounding electrode system at service; neutral must not be bonded downstream.

GEC sized from service conductors per NEC Table 250.66; EGC sized from OCPD rating per Table 250.122.

Grounding electrodes include 8-ft rod, 2 AWG copper ground ring at least 20 ft, plate, pipe, and concrete-encased electrode.

Single rod, pipe, or plate: 25 ohms or less, or supplement with an additional electrode.

Class A GFCI trips at 4–6 mA; GFPE for equipment often 30 mA or higher.

Equipment bonding jumpers maintain fault path across water meters, gas piping, and removable sections.

EGC can be wire, busbar, or listed metal raceway; must be continuous and sized for fault current.

Receptacle grounding terminal must be connected to EGC; no neutral-to-ground connection at receptacles.

One service per building or structure unless special occupancy or capacity exceptions apply.

Service conductors have short-circuit protection but no overload protection; service disconnect located nearest entry.

Service equipment must be listed and marked suitable for use as service equipment.

Working space: 30 in wide, 36 in deep for ≤600V, 6.5 ft high; more depth for higher voltages.

Panelboard dedicated space: 30 in wide, 36 in deep, 6 ft high, free of foreign piping and ducts.

Service-entrance conductor ampacity must carry calculated load; continuous load at 125%.

Main bonding jumper installed at service; grounding electrode conductor connected at service.

Panelboard neutral bar must be isolated from enclosure when not service equipment.

Motor branch conductors ≥125% of FLC from NEC tables; overload sized per nameplate service factor.

Motor disconnecting means within sight and within 50 ft; lockable open if out of sight.

Motor short-circuit protection from tables; inverse-time breaker up to 250% FLC for standard motors.

Motor feeder demand factors apply for multiple motors; largest motor adds 25%.

Generator transfer switch prevents backfeed; optional standby systems require load management.

HVAC hermetic compressor circuits use nameplate rated-load amps; branch conductor ≥125% RLA.

Motor control circuit conductors protected per control transformer and overload requirements.

Generator neutral grounding depends on transfer switch switched or unswitched neutral; separately derived system rules apply.

Transformer current: single-phase I = kVA×1000/V; three-phase I = kVA×1000/(√3×V).

Primary and secondary OCPD sized per NEC Table 450.3(B); next standard size permitted.

Transformer secondary conductors can use 10-ft or 25-ft tap rules with conditions.

Delta-wye transformer creates a separately derived system; X0 bonded to enclosure and EGC.

Dry-type transformer requires ventilation and clearances; install only where listed for the location.

Parallel transformers require same voltage ratio, impedance, and tap settings.

K-rated transformer handles harmonic loads; derating applies for nonlinear loads.

Transformer inrush current can trip fast-magnetic breakers; use dual-element fuses or thermal-magnetic devices.

Hazardous locations: Class I gases or vapors; Class II dust; Class III fibers or flyings; divisions or zones define probability.

Health care: life safety, critical, and equipment branches; essential electrical system transfer.

Swimming pools: equipotential bonding, GFCI protection, and no receptacles within 6 ft of pool edge.

Solar PV: rapid shutdown at array, DC labeling, and conductor sizing at 125% Isc.

Fire pumps: dedicated reliable power, listed controller, and no GFCI protection on fire pump circuits.

Assembly occupancies: emergency lighting and exit signs require battery or generator backup.

Agricultural buildings: equipotential plane in livestock areas and GFCI for receptacles.

Lockout/tagout: de-energize, lock, tag, test with properly rated meter before work.

Approach boundaries: limited, restricted, prohibited; arc flash PPE based on incident energy.

Plan review verifies load calculations, available fault current, interrupting ratings, voltage drop, and clearances.

Rough-in inspection occurs before concealment; final inspection after complete installation.

Arc flash label includes nominal voltage, available fault current, clearing time, and incident energy.

Energized work requires permit and justification; PPE and insulated tools required.

Confined space entry requires permit, atmospheric testing, attendant, and rescue plan.