Journeyman Electrician flashcards

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

Ohm's Law

The current in a circuit equals the voltage divided by the resistance, written I = E ÷ R. Rearranged, E = I × R and R = E ÷ I.

Power Formula

True power in watts equals voltage times current in a resistive circuit, P = E × I, and may also be written as I²R or E² ÷ R.

Series Circuit Current

In a series circuit the current is identical through every component, total resistance is the sum of the resistances, and the voltage divides in proportion to resistance.

Nonmetallic-Sheathed Cable Uses

Type NM cable is permitted in normally dry locations such as dwellings, but not in wet locations, in masonry voids, or where subject to physical damage.

Conduit as Grounding Means

Rigid metal conduit, IMC, and EMT are recognized equipment grounding conductors, while PVC conduit is not, so a separate equipment grounding conductor must be installed.

Box Fill for 12 AWG

Each 12 AWG conductor counts as 2.25 cubic inches of box volume, and each yoke-mounted device counts as two conductors when sizing boxes under NEC 314.16.

Grounding Electrode Conductor Sizing

The conductor connecting the grounded service point to the grounding electrode is sized from NEC Table 250.66 using the largest ungrounded service conductor.

Equipment Grounding Conductor Sizing

The equipment grounding conductor provides a low-impedance fault path and is sized from NEC Table 250.122 using the rating of the overcurrent device ahead of the equipment.

Class A GFCI Threshold

A Class A ground-fault circuit interrupter trips at 4 to 6 milliamperes of ground-fault current and provides personnel protection on 120/240 volt circuits.

Small Conductor Rule

NEC 240.4(D) limits overcurrent protection to 15 amperes for 14 AWG, 20 amperes for 12 AWG, and 30 amperes for 10 AWG copper conductors.

Interrupting Rating Requirement

An overcurrent device's interrupting rating must equal or exceed the available fault current at its line terminals, otherwise the device may fail violently during a short circuit.

Next Size Up Rule

For devices rated 800 amperes or less, the next higher standard overcurrent rating may be used when the conductor ampacity does not match a standard rating and the circuit is not multioutlet.

Continuous Load 125 Percent

A continuous load operates for 3 hours or more, and branch-circuit conductors plus overcurrent devices must be sized at not less than 125 percent of it.

Dwelling Lighting Load

Dwelling general lighting load is calculated at 3 volt-amperes per square foot, with small-appliance and laundry branch circuits added separately at 1500 VA each.

Commercial Receptacle Load

Each receptacle outlet on a commercial branch circuit is calculated at 180 volt-amperes, so ten outlets equal 1800 VA on a 20 ampere circuit.

Ampacity Correction and Adjustment

Conductor ampacity from Table 310.16 must be corrected for ambient temperature and adjusted for the number of current-carrying conductors sharing a raceway.

Bundled Conductor Derating

Four to six current-carrying conductors in one raceway require 80 percent adjustment, seven to nine require 70 percent, and ten to twenty require 50 percent.

Parallel Conductor Minimum Size

Parallel conductors must be 1/0 AWG or larger and identical in length, conductor material, size, insulation type, and termination method.

Working Space Depth

NEC 110.26 requires clear working space at least 3 feet deep, 30 inches wide, and 6.5 feet high, with depth increasing for higher voltages.

Straight Pull Box Length

A box or conduit body used for a straight pull must be at least eight times the trade size of the largest raceway entering it.

Panelboard Location Restrictions

Overcurrent devices must not be installed in bathrooms or clothes closets and must not be located over steps; they must remain readily accessible.

Motor Conductor Sizing

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

Motor Overload Protection

Overload protection for a motor with a marked service factor of 1.15 is typically set at 125 percent of the nameplate full-load current.

Transformer Primary Protection

For transformers with a primary current over 9 amperes, primary overcurrent protection is set at not more than 125 percent of rated primary current.

Hazardous Location Classes

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

Division 1 Versus Division 2

Division 1 covers hazardous conditions that exist under normal operation, while Division 2 covers conditions that occur only under abnormal or fault conditions.

Pool Equipotential Bonding

Around permanently installed pools, metal parts, forming shells, and reinforcing steel must be bonded together into an equipotential grid per NEC 680.26.

Test Before Touch

Circuits must be verified de-energized with a tester rated for the voltage before work begins, and all conductors are treated as energized until tested.

Lockout Tagout Verification

Each worker applies a personal lock and tag to the energy-isolating device, then verifies isolation by attempting to start the equipment.

Limited Approach Boundary

The limited approach boundary is the distance from exposed energized parts that unqualified persons must not cross, and it increases with system voltage.

Construction Site GFCI

Temporary 125 volt, 15 and 20 ampere receptacles on construction sites require Class A ground-fault circuit interrupter protection under NEC 590.6.

Conduit Bend Limit

No more than 360 degrees of total bends is permitted between pull points in a conduit run, counting all offsets, saddles, and elbows.