AR Electrician flashcards

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

Ohm's Law

Ohm's law states that voltage equals current multiplied by resistance, E = I × R; rearranged, current equals voltage divided by resistance and resistance equals voltage divided by current.

RMS Versus Peak Voltage

For a sine wave, the RMS value equals 0.707 times the peak value and the peak equals 1.414 times the RMS value, so 120 V RMS corresponds to about 170 V peak.

Three-Phase Power Formula

For a balanced three-phase load, power in watts equals 1.732 times line voltage times line current times the power factor of the load.

Conductor Resistance Formula

Resistance equals a constant K times length in feet divided by circular mil area; K is about 12.9 for copper and 21.2 for aluminum at 75 degrees Celsius.

NM Cable Restrictions

Nonmetallic-sheathed cable is restricted to dry locations and may not be installed in wet locations, inside raceways, or where it would be subject to physical damage.

EMT Support Spacing

Electrical metallic tubing must be fastened within 3 ft of each box or fitting and supported at intervals not exceeding 10 ft along the run.

Rigid Metal Conduit Burial

Rigid metal conduit buried in earth requires a minimum cover of 6 in, while PVC conduit 2 in and smaller requires 18 in of cover.

Service Drop Clearances

Overhead service-drop conductors must be at least 10 ft above grade at the drip loop, 12 ft over residential driveways, and 18 ft over public streets.

Dwelling Service Disconnecting Means

A one-family dwelling service disconnecting means must be rated at least 100 A, installed as a single means, and located nearest the point of service conductor entry.

Small-Appliance Branch Circuits

Dwelling unit kitchens require at least two 20 A small-appliance branch circuits supplying countertop receptacles, and no other outlets may be connected to them.

Ground Rod Ohm Rule

A single driven ground rod must show 25 ohms or less resistance to earth, or it must be supplemented by one additional electrode at least 6 ft away.

Grounding Electrode Conductor Sizing

The grounding electrode conductor is sized using Table 250.66, which bases its minimum size on the size of the largest service-entrance or feeder conductor.

Equipment Grounding Conductor Sizing

The equipment grounding conductor is sized from Table 250.122 based on the rating of the overcurrent device protecting the circuit conductors.

Metal Water Pipe Bonding

Metal water piping must be bonded to the grounding system within 5 ft of where it enters the building and qualifies as an electrode only with 10 ft of earth contact.

Next-Size-Up Rule

The next higher standard overcurrent device may be used where conductor ampacity is 800 A or less, the circuit is not multioutlet, and the device does not exceed 800 A.

Standard Overcurrent Device Ratings

Standard ratings include 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300, and 400 amperes.

Service Ground-Fault Protection

Ground-fault protection of equipment is required for solidly grounded wye services rated 1000 A or more with more than 150 V to ground, limited to 1200 A pickup.

Box Fill Conductor Volumes

Conductor volume allowances are 2.0 cubic inches for 14 AWG, 2.25 for 12 AWG, 2.5 for 10 AWG, and 3.0 for 8 AWG copper conductors.

Conduit Fill Percentages

Raceway fill may not exceed 53 percent for one conductor, 31 percent for two conductors, or 40 percent for three or more conductors.

Free Conductor Length

At least 6 in of free conductor must be left at each box, extending at least 3 in beyond the box opening to allow splices and device connections.

Dwelling General Lighting Load

Dwelling unit general lighting and general-use receptacles are calculated at 3 volt-amperes per square foot of floor area, excluding open porches and garages.

Dwelling Lighting Demand Factors

The first 3000 VA of dwelling lighting load is taken at 100 percent, the next 3000 VA at 35 percent, and any remaining volt-amperes at 25 percent.

Range Demand One Unit

Table 220.55 permits a demand load of 8 kW for a single household electric range with a nameplate rating of 12 kW or less.

Motor Branch Conductor Sizing

Motor branch-circuit conductors must have an ampacity of at least 125 percent of the motor full-load current taken from Table 430.250.

Motor Overload Protection

Motor overload protection is normally selected at 115 to 125 percent of the motor nameplate full-load current, with higher values allowed for certain slow-starting motors.

Motor Short-Circuit Protection Values

Table 430.52 permits an inverse-time circuit breaker at 250 percent and a dual-element time-delay fuse at 175 percent of motor full-load current.

Class I Division 1

A Class I Division 1 location is one where ignitable concentrations of flammable gases or vapors exist under normal operating conditions or frequently during repair work.

Pool Equipotential Bonding

Permanently installed pools require all metal parts, including the shell and fittings, to be bonded together with a solid 8 AWG copper conductor.

Patient Care Redundant Grounding

Patient care areas of health care facilities require a copper equipment grounding conductor installed in the raceway in addition to the raceway itself as a ground path.

Working Space Depth

For equipment rated 600 V or less under condition 1, the working space must be at least 36 in deep, 30 in wide, and 6 ft 6 in high.

Arc Flash PPE Selection

NFPA 70E requires arc-rated clothing and personal protective equipment chosen according to the incident energy exposure or arc flash PPE category of the task.

Lockout Tagout Sequence

The procedure is to de-energize the equipment, verify the absence of voltage with a tested meter, release stored energy, and apply a lock and tag.