gh-ec-electrical-wiring-industrial flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Arc Flash Boundary

The distance at which incident energy from an arc flash equals 1.2 cal/cm², the threshold for second-degree burns; used to define where arc-rated PPE is required.

Electrically Safe Work Condition

A state in which the conductor or circuit part has been disconnected, isolated, locked out, and tested to verify the absence of voltage, with grounds applied where required.

Three-Phase Power Formula

For a balanced three-phase load, real power equals the square root of three times line voltage times line current times power factor.

Voltage Drop Formula

Single-phase voltage drop approximates 2KIL divided by circular mils; three-phase approximates 1.732 times KIL divided by circular mils, where K is conductor resistivity.

Ampacity Adjustment Factors

Conductor ampacity from the ampacity table is reduced for elevated ambient temperature and for more than three current-carrying conductors in a raceway or cable.

Parallel Conductor Requirements

Parallel conductors must be 1/0 AWG or larger and have the same length, material, size, insulation, and termination to ensure equal current sharing.

Raceway Fill 40 Percent

For three or more conductors, the total cross-sectional area of conductors including insulation cannot exceed 40 percent of the raceway interior area.

Box Fill Calculation

Box volume must accommodate conductor counts, device yokes, grounding conductors, clamps, and support fittings, each converted to volume allowances per the box fill table.

Continuous Load 125 Percent

Branch-circuit and feeder overcurrent devices must be sized at not less than 125 percent of continuous load plus 100 percent of noncontinuous load unless listed for 100 percent operation.

Small Conductor Protection Limits

Unless permitted by a specific exception, 14 AWG copper is limited to 15 A, 12 AWG to 20 A, and 10 AWG to 30 A overcurrent protection.

Equipment Grounding Conductor Sizing

Equipment grounding conductors are sized from the overcurrent device rating protecting the circuit, and must be increased proportionally when circuit conductors are upsized for voltage drop.

System Bonding Jumper

The connection between the grounded conductor and the equipment grounding conductor at the service or separately derived system; it must not exist on the load side.

Motor Branch Conductor Sizing

Motor branch-circuit conductors must have ampacity of at least 125 percent of the motor full-load current taken from the motor tables, not the nameplate value.

Motor Overload Protection

Overload relays protect the motor from sustained overcurrent and are sized from nameplate full-load current, typically 115 to 125 percent for service-factor 1.15 motors.

Transformer Current Calculation

Primary or secondary current equals transformer kVA times 1000 divided by winding voltage; for three-phase, divide additionally by the square root of three.

Separately Derived System Grounding

A transformer secondary requires a system bonding jumper and a grounding electrode conductor to the nearest grounding electrode, with the neutral isolated downstream.

Class I Division 1

A location where flammable gases or vapors are present under normal operating conditions; requires explosion-proof or intrinsically safe equipment and conduit seals within 18 inches.

Intrinsic Safety

A protection method that limits electrical energy in a hazardous area to levels below ignition thresholds, using barriers or isolators, identified with blue conductors or markings.

Limited Approach Boundary

A shock protection boundary around exposed energized parts that unqualified persons may not cross; qualified persons crossing it must use appropriate protective equipment.

Power Factor Correction

Capacitor kilovolt-amperes reactive equals real power times the difference between the tangents of the initial and desired power factor angles.

Synchronous Speed Formula

Motor synchronous speed in revolutions per minute equals 120 times the supply frequency in hertz divided by the number of motor poles.

Conductor Color Coding

Grounded conductors are white or gray; equipment grounding conductors are green, green with yellow stripe, or bare; the high-leg of a four-wire delta is marked orange.

Type NM-B Cable Limits

Nonmetallic-sheathed cable is permitted only in dry locations and is prohibited in hazardous locations, outdoors in raceways, and where subject to physical damage.

360 Degree Bend Limit

No more than 360 degrees of bends, equivalent to four quarter bends, is permitted between pull points in a raceway run.

Standard Overcurrent Ratings

Standard ampere ratings include 15, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300, 350, 400, 450, 500, 600, 700, 800, 1000, and 1200 amperes.

GFCI Protection Locations

Ground-fault circuit-interrupter protection is required for 125-volt receptacles in bathrooms, kitchens, garages, outdoors, crawl spaces, unfinished basements, and near sinks.

Grounding Electrode System

Metal water pipe, building steel, concrete-encased electrode, ground ring, rods, and plates that are present must be bonded together into a single grounding electrode system.

Ground-Fault Protection of Equipment

Services rated 1000 amperes or more at 480Y/277 volts require ground-fault protection with a maximum setting of 1200 amperes and a coordinated time delay.

Motor Disconnecting Means

A disconnecting means must be within sight of the motor and controller or lockable open, and sized at least 115 percent of the motor full-load current.

Motor Short-Circuit Protection

Branch-circuit short-circuit protection for motors is sized as a percentage of full-load current from the motor protection table, with the next higher standard rating permitted.

Transformer Inrush Current

Energizing a transformer draws magnetizing inrush of roughly 8 to 12 times rated current for a few cycles, so time-delay protective devices are selected to avoid nuisance tripping.

Zone Classification System

Class I locations may be classified by zones instead of divisions: Zone 0 for continuous presence, Zone 1 for normal conditions, and Zone 2 for abnormal conditions.