Master Electrician flashcards

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

Ohm's law formula

For a resistive circuit, voltage equals current times resistance (E = I × R); power equals voltage times current, or current squared times resistance.

Three-phase power formula

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

Continuous load definition

A load expected to operate at maximum current for three hours or more; conductors and overcurrent devices are sized at 125 percent where the Code requires.

Voltage drop formula

Single-phase voltage drop approximately equals two times conductor constant K times current times one-way length divided by circular mils; three-phase uses square root of three.

NM cable support spacing

Nonmetallic-sheathed cable must be secured within 12 inches of boxes and at intervals not exceeding 4.5 feet along runs.

Raceway conductor fill

For three or more conductors in a raceway, total conductor area may not exceed 40 percent of the raceway interior cross-sectional area.

Box fill counting

Each 14 AWG conductor counts 2.0 cubic inches, 12 AWG counts 2.25, and 10 AWG counts 2.5; clamps, devices, and grounds add volume.

Small appliance circuits

Dwelling kitchens require at least two 20-ampere small-appliance branch circuits, each calculated at 1,500 volt-amperes, serving countertop receptacles.

General lighting load

For dwelling units, the general lighting load is calculated at 3 volt-amperes per square foot of floor area, with demand factors applied.

Receptacle load calculation

In non-dwelling occupancies, each receptacle outlet is calculated at 180 volt-amperes per yoke unless the load is known to be greater.

Interrupting rating

An overcurrent device's interrupting rating must equal or exceed the available fault current at its line terminals; otherwise it may fail violently.

Motor short-circuit protection

Motor branch-circuit short-circuit and ground-fault protection is selected from Code tables and is separate from overload protection, which protects the motor from overheating.

Series-rated system

A series-rated combination must be tested and listed as a unit; replacing one device with an unlisted type voids the rating.

Grounding electrode conductor

The grounding electrode conductor is sized from the service-entrance conductor using the Code table, and it connects the grounded system to the grounding electrode system.

Equipment grounding conductor

The equipment grounding conductor provides a low-impedance fault path and is sized from the overcurrent device rating using the Code table.

GFCI trip level

A Class A ground-fault circuit interrupter trips at 4 to 6 milliamperes of ground-fault current and is intended to protect personnel.

Main bonding jumper

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

Service disconnect location

Service disconnecting means must be installed at a readily accessible location nearest the point of entry of service conductors, either outside or inside nearest entry.

Working clearance depth

For equipment operating at 600 volts or less, the minimum working space depth is 36 inches, with 30-inch width and 6.5-foot height.

Dedicated panel space

Panelboards require a dedicated space 30 inches wide, 36 inches deep, and 6 feet high, kept free of foreign piping and ducts.

Motor conductor sizing

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

Motor disconnect location

A motor disconnecting means must be within sight of the motor and within 50 feet, unless the disconnecting means is capable of being locked open.

Generator transfer switch

A transfer switch prevents a generator from backfeeding the utility supply by disconnecting the normal source before connecting the generator.

HVAC compressor circuit

Hermetic refrigerant motor-compressor branch circuits are sized from the nameplate rated-load amperes, not from standard motor full-load current tables.

Transformer current formula

Single-phase transformer current equals kVA times 1,000 divided by voltage; for three-phase, divide by the square root of three times voltage.

Transformer secondary tap

Secondary conductors may be protected by the primary device under the 25-foot tap rule only when specific conditions for length and enclosure are met.

System bonding jumper

In a separately derived system, the system bonding jumper connects the transformer secondary neutral to the equipment grounding conductor and enclosure.

Hazardous location classification

Class I locations contain flammable gases or vapors; Class II contains combustible dust; Class III contains ignitable fibers or flyings.

Swimming pool bonding

Equipotential bonding around a swimming pool ties together metal parts, pool water, and equipment to reduce voltage gradients.

Health care critical branch

The critical branch supplies selected patient-care and life-support loads and must be separate from the equipment branch.

Lockout tagout

Before work, the circuit must be de-energized, locked, tagged, and tested with a meter rated for the voltage to verify absence of voltage.

Plan review fault current

Plan review checks available fault current against equipment interrupting and withstand ratings, plus conductor ampacity, voltage drop, and working clearances.