NCCER Electrical flashcards
NCCER Electrical · Build recall with a focused review session.
32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Lockout/tagout verification
- After isolating and locking the disconnect, release stored energy and use a voltage tester rated for the circuit to confirm zero voltage at the point of work.
- Class A GFCI threshold
- A Class A ground-fault circuit interrupter trips when it senses 4 to 6 milliamperes of current imbalance between the ungrounded and grounded conductors.
- Arc flash burn threshold
- 1.2 calories per square centimeter is the incident-energy level commonly used as the threshold for a second-degree burn on bare skin.
- Rubber glove Class 00
- Class 00 rubber insulating gloves are rated for use up to 500 volts AC and must be air-tested and electrically retested on the required schedule.
- Let-go current threshold
- The let-go threshold is about 10 to 15 milliamperes for most adults; at higher currents, a person may be unable to release an energized conductor.
- Ohm's law
- Voltage equals current times resistance (V = I × R); it applies to resistive portions of DC and AC circuits and can be rearranged to find current or resistance.
- Series circuit rules
- In a series circuit, current is the same through every component, resistances add, and source voltage divides in proportion to the individual resistance values.
- Parallel circuit rules
- In a parallel circuit, voltage is the same across every branch, branch currents add, and total resistance is found from the reciprocal of the sum of reciprocals.
- 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.
- Power factor
- Power factor is real power divided by apparent power, equal to the cosine of the angle between voltage and current for sinusoidal waveforms.
- Continuous load 125 percent
- Branch-circuit conductors and overcurrent devices supplying a continuous load must be sized at not less than 125 percent of the continuous load before other adjustments.
- Conductor bundling derating
- When four to six current-carrying conductors share a raceway or cable, the NEC adjustment table requires ampacity to be reduced to 80 percent of the table value.
- Box fill calculation
- Box fill is the sum of conductor volumes plus fittings, devices, and equipment-grounding allowances; compare the total to the box volume from NEC Table 314.16(A).
- Voltage drop recommendation
- NEC informational notes recommend no more than 3 percent voltage drop on a branch circuit and 5 percent total from the service to the farthest outlet.
- Working space 110.26
- Energized equipment requires a clear working space at least 30 inches wide, 36 inches deep for 0–150 volts to ground, and 6.5 feet high.
- Dwelling receptacle spacing
- In dwelling units, no point along the floor line may be more than 6 feet from a receptacle outlet, and wall spaces 2 feet or wider require an outlet.
- 360-degree bend rule
- No more than 360 degrees of total bends, including offsets, is permitted between pull points in a raceway run.
- EMT support intervals
- Electrical metallic tubing must be supported within 3 feet of each box or fitting and at intervals not exceeding 10 feet.
- Conduit fill percentages
- NEC Chapter 9 limits raceway fill to 53 percent for one conductor, 31 percent for two, and 40 percent for three or more conductors.
- LFMC support
- Liquidtight flexible metal conduit must be supported within 12 inches of each box and at intervals not exceeding 4.5 feet.
- RMC support intervals
- Rigid metal conduit and intermediate metal conduit must be supported within 3 feet of each box and at intervals not exceeding 10 feet.
- 12 AWG copper ampacity
- A 12 AWG copper conductor with 60°C terminations is generally limited to 20 amperes; the 75°C column permits 25 amperes where terminations are rated for it.
- Grounded conductor color
- The grounded circuit conductor must be identified by white or gray, or by three continuous white stripes on other than green insulation.
- THHN insulation rating
- THHN is a 90°C dry-location thermoplastic insulation with a nylon jacket; in wet locations its ampacity is limited to the 75°C column.
- Neutral as current-carrying
- The neutral counts as a current-carrying conductor when it carries the unbalanced current of a wye circuit, but not for a balanced three-phase wye feeder.
- Splice location rule
- Conductors must be spliced only in enclosures such as boxes or conduit bodies that are accessible without removing building finish.
- Grounding electrode conductor sizing
- The grounding electrode conductor is sized from NEC Table 250.66 based on the largest ungrounded service conductor; it connects the service neutral to the grounding electrode system.
- Equipment grounding conductor sizing
- The equipment grounding conductor is sized from NEC Table 250.122 based on the rating of the overcurrent device protecting the circuit.
- 25-ohm ground rule
- A single rod, pipe, or plate electrode must have a resistance to earth of 25 ohms or less, or a second electrode must be installed.
- Main bonding jumper
- The main bonding jumper connects the grounded service conductor to the service equipment enclosure and the equipment grounding conductor at the service.
- Motor branch conductor sizing
- Motor branch-circuit conductors must have an ampacity of at least 125 percent of the motor full-load current from the appropriate Article 430 table.
- Motor overload protection
- Overload relays protect a motor from sustained overcurrent; they are generally set at 125 percent of nameplate full-load current when the service factor is at least 1.15, and 115 percent otherwise.