IA Electrician cheat sheet

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

Series circuit: total resistance is the sum of resistances; current is the same through all elements; voltage divides in proportion to resistance.

Parallel circuit: 1/RT = 1/R1 + 1/R2 + ...; voltage is the same across branches; current divides inversely with resistance.

AC power relationships: real power P = VI cosθ; apparent power S = VI; reactive power Q = VI sinθ.

Balanced three-phase power: P = √3 × VL × IL × power factor.

Impedance: Z = √(R² + X²); inductive reactance XL = 2πfL; capacitive reactance XC = 1/(2πfC).

Transformer turns ratio: VP/VS = NP/NS; current ratio is inverse of the voltage ratio.

Conductor resistance: R = ρL/A; resistance increases with temperature for copper and aluminum.

Kirchhoff's laws: current law sums currents at a node to zero; voltage law sums voltages around a closed loop to zero.

Only qualified persons may work on or near exposed energized conductors; unqualified persons must be protected from electrical hazards.

De-energize, lock out, tag out, release stored energy, and verify absence of voltage before working on electrical equipment.

Approach boundaries include limited, restricted, and prohibited boundaries; voltage, PPE, and distance determine who may cross each.

A Class A GFCI trips at approximately 4 to 6 mA of ground-fault current and protects personnel from electric shock.

Arc-flash hazard is evaluated by incident energy and arc-flash boundary; energized work requires justification and appropriate PPE.

Nonconductive ladders are used near electrical equipment; portable ladders are set at approximately a 4:1 angle.

Portable cords must be inspected, protected from damage, and used with GFCI protection where required on construction sites.

For an electrical shock victim, disconnect the source before touching the person, then call emergency services and provide first aid, CPR, or AED use as trained.

A one-family dwelling service must have a minimum rating of 100 amperes, unless code exceptions permit otherwise.

Service equipment may have no more than six disconnecting means grouped in one location, with each disconnect marked for the load served.

The service grounded conductor is bonded to the service enclosure and grounding electrode system only at the service disconnecting means.

Dwelling units require at least two 20-ampere small-appliance branch circuits for kitchen, dining, pantry, and similar areas.

Laundry areas require a 20-ampere branch circuit; bathroom receptacle circuits require 20-ampere GFCI protection.

In dwelling units, receptacle outlets along walls must be arranged so no point on the wall is more than 6 feet from a receptacle.

Recommended voltage drop is no more than 3 percent on a branch circuit and no more than 5 percent total from service to load.

Continuous loads require branch-circuit and feeder sizing at 125 percent of the continuous load plus 100 percent of noncontinuous load, unless otherwise permitted.

Ampacity is selected from the applicable table, commonly Table 310.16, based on 30°C ambient temperature and termination temperature ratings.

Ambient temperature correction factors and conductor adjustment factors must be applied where conditions require.

Where four to six current-carrying conductors share a raceway or cable, ampacity is adjusted to 80 percent; additional conductors have lower adjustment factors.

Small-conductor overcurrent limits include 15 A for 14 AWG copper, 20 A for 12 AWG copper, and 30 A for 10 AWG copper, subject to exceptions.

The next higher standard overcurrent device rating is permitted where conductor ampacity does not match a standard rating, if the device does not exceed 800 A and conditions of 240.4(B) are met.

Raceway conductor fill limits are 53 percent for one conductor, 31 percent for two conductors, and 40 percent for three or more conductors.

NM-B cable ampacity is taken from the 60°C column of the ampacity tables, per NEC 334.80.

Conductor termination temperature ratings limit the usable ampacity; equipment rated 75°C or 90°C may permit use of that column only when all components are rated accordingly.

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

Between pull points, a raceway may contain no more than 360 degrees of total bends.

NM cable must be secured within 12 inches of each box and at intervals not exceeding 4.5 feet, with protection where subject to damage.

Rigid metal conduit and intermediate metal conduit are recognized equipment grounding conductors; PVC conduit requires a separate equipment grounding conductor.

Expansion fittings are required where raceways cross building expansion joints or where thermal expansion is expected.

Bushings are required where conductors 4 AWG and larger enter boxes or raceways to protect conductor insulation.

Liquidtight flexible metal conduit is permitted only with listed fittings and within the length, size, and grounding limitations of the code.

Cable trays must be supported and installed so cables are protected from damage and maintained within the allowable fill.

Box fill is calculated using NEC 314.16 volume allowances for conductors, clamps, devices, and equipment grounding conductors.

Each 14 AWG conductor requires 2.0 cubic inches, 12 AWG requires 2.25 cubic inches, and 10 AWG requires 2.5 cubic inches.

Each device yoke or strap counts as two conductor volumes based on the largest conductor connected to the device.

One or more equipment grounding conductors count as a single volume based on the largest equipment grounding conductor.

Junction boxes, splices, and termination points must remain accessible and cannot be concealed behind permanent building finish.

For raceway pulls, the minimum box dimension is 8 times the trade diameter for straight pulls and 6 times for angle or U pulls.

Enclosures in wet locations must be listed for the location and arranged to drain; unused openings must be closed.

Box extension rings must provide sufficient volume and must not reduce the required box fill volume.

NEC Table 210.21(B)(3) permits 15-ampere receptacles on 20-ampere branch circuits under specified conditions.

Tamper-resistant receptacles are required in dwelling units and in other specified locations such as child-care facilities.

Receptacles in bathrooms, kitchens, garages, outdoors, and other specified wet or damp locations require GFCI protection.

Receptacles in wet locations require weather-resistant receptacles and listed weatherproof covers, whether or not the device is in use.

A GFCI receptacle may replace an ungrounded receptacle where no equipment grounding conductor exists; it must be marked 'No Equipment Ground.'

A neutral conductor is generally required at switch locations in dwelling units for certain switch-controlled loads, per NEC 404.2(C).

Dimmers and switches must be listed for the load type and rating; dimmers are not interchangeable with general-use snap switches.

AFCI protection is required for specified 120-volt, 15- and 20-ampere dwelling-unit branch circuits supplying outlets in designated areas.

Overcurrent protection must protect conductors against overcurrent and must not exceed conductor ampacity except where specific code rules permit.

Standard overcurrent device ratings include 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, and 100 amperes.

The next higher standard overcurrent device rating is permitted only when the device does not exceed 800 A and the conditions of 240.4(B) are satisfied.

Series-rated systems must use listed combinations of upstream and downstream devices; devices cannot be mixed unless tested and listed together.

Motor overload protection is separate from branch-circuit short-circuit and ground-fault protection.

Ground-fault protection of equipment is required for certain 480Y/277-volt service disconnects rated 1000 amperes or more.

GFCI and AFCI circuit breakers must be listed for the purpose and must be connected so the protected circuit neutral is not shared improperly.

Fuses and circuit breakers have time-current characteristics; selective coordination considers both trip curves and fault levels.

The grounded conductor is the neutral; the equipment grounding conductor is green, green with yellow stripe, or bare.

The service neutral is bonded to the service enclosure and grounding electrode system at the service disconnect only.

Grounding electrode systems may include ground rods, pipes, plates, concrete-encased electrodes, water pipes, and ground rings as permitted.

A single ground rod or pipe electrode with resistance over 25 ohms requires a supplemental electrode, unless a single electrode achieves 25 ohms or less.

Equipment grounding conductor size is selected from Table 250.122 based on the overcurrent device rating, with upsizing rules when circuit conductors are increased.

Bonding jumpers are required around water meters, gas piping, and other metallic systems to ensure electrical continuity.

Separately derived systems must have their grounded conductor bonded at the source and connected to a grounding electrode system.

Receptacle grounding continuity must be maintained through the equipment grounding conductor, which may be a wire or a recognized raceway type.

Motor branch-circuit conductors must have ampacity of at least 125 percent of the motor full-load current, unless Article 430 permits otherwise.

Motor overload protection is sized from motor nameplate current and protects the motor from overheating.

Motor branch-circuit short-circuit and ground-fault protection is selected from Table 430.52 and may be increased under specified conditions.

A motor disconnecting means must be within sight of the motor and controller, or lockable where not within sight; 'within sight' means not more than 50 feet.

Motor controllers must be rated for the motor and must provide the required starting and stopping functions.

For hermetic refrigerant motor-compressors, nameplate minimum circuit ampacity (MCA) sizes conductors and maximum overcurrent protection (MOP) sizes branch-circuit protection.

HVAC equipment disconnects must be located within sight of the equipment and be capable of being locked in the open position.

Two-wire control provides automatic restart; three-wire control with holding contacts provides low-voltage release and manual restart after power loss.

Hazardous locations are classified by Class I gases and vapors, Class II dusts, and Class III fibers; divisions or zones indicate likelihood of hazard.

Class I, Division 1 installations require explosionproof equipment and conduit seals within 18 inches of certain enclosures.

Wet-location receptacles require GFCI protection, weather-resistant devices, and listed weatherproof covers.

Swimming pool installations require equipotential bonding of metallic parts and GFCI protection for specified receptacles and equipment.

Receptacles serving swimming pools must be at least 6 feet from the inside wall of the pool unless specifically permitted otherwise.

Temporary wiring on construction sites requires GFCI protection for receptacles and protection of conductors from damage.

Agricultural buildings may require an equipotential plane and GFCI protection for receptacles in specified areas.

Health care facilities have additional grounding, redundant grounding, and isolated power requirements for critical-care areas.

Dwelling-unit general lighting load is calculated at 3 VA per square foot of floor area, then demand factors are applied.

Small-appliance and laundry branch circuits are each calculated at 1500 VA and may be subject to demand factors.

Standard calculation for a service or feeder includes general lighting, small-appliance, laundry, appliance, range, dryer, and heating or cooling loads.

Continuous loads are calculated at 125 percent; noncontinuous loads are calculated at 100 percent for conductor and overcurrent sizing unless otherwise permitted.

Neutral load is based on the maximum unbalanced load and may be reduced by demand factors where the code permits.

Box fill and conduit fill calculations use Chapter 9 area tables and the volume allowances in Article 314.

Single-phase voltage drop: VD = 2 × K × I × L / CM, where K is conductor resistivity, I is amperes, L is one-way length, and CM is circular mils.

Plan reading requires identifying scale, legend, symbols, panel schedules, circuit numbers, and specification notes before computing loads.