MTTC Electrical Trade Test flashcards

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

Qualified Person

A person who has demonstrated skills and knowledge related to electrical equipment construction and operation and has received safety training on the hazards involved, per NFPA 70E.

Limited Approach Boundary

A distance from an exposed energized conductor that unqualified persons may not cross unless escorted and protected; for 600 V class equipment it is typically 10 ft.

Lockout/Tagout Verification

The step after isolating and locking energy sources where a voltage tester, proved functional before and after, confirms the circuit is de-energized.

Ohm's Law

The relationship E = I x R, where voltage in volts equals current in amperes multiplied by resistance in ohms. Combined with power, P = E x I.

Three-Phase Power Formula

Real power equals the square root of three times line voltage times line current times power factor; apparent power omits the power factor term.

Synchronous Speed

The rotating speed of a motor's magnetic field, calculated as 120 times frequency divided by the number of poles; a 4-pole motor on 60 Hz runs at 1800 rpm.

Impedance

The total opposition to alternating current, combining resistance and net reactance as the square root of R squared plus the square of inductive minus capacitive reactance.

RMS Value

The effective value of a sine wave, equal to 0.707 times the peak value; it produces the same heating effect as an equal DC value.

Box Fill Calculation

A method summing conductor equivalents, clamps, devices, and grounding conductors, then multiplying by the volume allowance per conductor from Table 314.16(B).

NM-B Cable Limits

Nonmetallic sheathed cable is prohibited in wet locations, masonry cavities, and outdoors in raceways, and needs protection where within 1-1/4 in of framing surfaces.

Ampacity Adjustment

When more than three current-carrying conductors share a raceway, Table 310.15(C)(1) reduces ampacity: 4-6 conductors to 80%, 7-9 to 70%, 10-20 to 50%.

EMT Support Rules

Electrical metallic tubing must be supported within 3 ft of each box and at intervals not exceeding 10 ft along the run, using listed straps or clamps.

Conduit Fill Percentages

Chapter 9 permits one conductor at 53%, two at 31%, and more than two at 40% of the raceway internal cross-sectional area.

Voltage Drop Formula

Single-phase drop equals 2 times K times current times length divided by circular mils; three-phase uses the square root of three in place of the 2.

Parallel Conductors

Conductors run in parallel must share the same length, material, insulation, and termination, with a minimum size of 1/0 AWG in most installations.

THHN Insulation Rating

Thermoplastic high-heat nylon insulation rated 90 degrees C dry and 75 degrees C wet; ampacity is limited by the termination rating, commonly 75 degrees C.

Continuous Load Rule

A load operating at maximum current for three hours or more must be calculated at 125% of its rating when sizing branch circuits, feeders, and overcurrent devices.

Small-Appliance Circuit

A 20 A branch circuit serving dwelling kitchen receptacle outlets; at least two are required, and they may not serve lighting outlets.

Feeder Tap Rule

A tap up to 10 ft long may use conductors at least one-tenth the overcurrent device rating if protected from damage and terminated in a single device.

Dwelling Lighting Load

General lighting in a dwelling is calculated at 3 volt-amperes per square foot, then demand factors from Table 220.42 are applied to the total.

Motor Conductor Sizing

Branch-circuit conductors supplying a single motor must have ampacity at least 125% of the motor full-load current from the applicable Article 430 table.

Motor Overload Protection

Running overload protection is sized from the motor nameplate service factor and temperature rise, protecting the winding from sustained excess current, not short circuits.

Motor Disconnect Rating

The disconnecting means must be rated at least 115% of the motor full-load current and located within sight of the motor or lockable open.

Reduced-Voltage Starting

A starting method that lowers voltage during acceleration, reducing inrush current but also reducing starting torque in proportion to the square of the voltage reduction.

Grounding Electrode Conductor

The conductor connecting the grounded service conductor to the grounding electrode; sized from Table 250.66 based on the largest ungrounded service conductor.

Equipment Grounding Conductor

The conductive path connecting equipment enclosures to the system grounding point; sized from Table 250.122 based on the overcurrent device rating.

Series Rating

An arrangement where a downstream breaker with lower interrupting rating is protected by an upstream current-limiting device, only when listed and marked as a combination.

GFPE Requirement

Ground-fault protection of equipment is required for solidly grounded wye services over 150 V to ground and 1000 A or more, with settings not exceeding 1200 A.

Insulation Resistance Test

A DC overvoltage test measuring leakage in megohms; readings below 1 megohm, or below 1 megohm per 1000 test volts, indicate degraded insulation.

Clamp Meter Residual Reading

Placing the clamp around all circuit conductors together should read zero; any residual current indicates leakage or a ground fault on the circuit.

Motor Winding Resistance Test

Measuring phase-to-phase and phase-to-ground resistance detects opens (infinite), shorted turns (near zero), and grounds (low resistance to the frame).

Performance Assessment

An evaluation in which learners demonstrate a trade task such as conduit bending or motor wiring against a rubric covering safety, code compliance, and workmanship.

Formative Assessment

A low-stakes check during instruction, such as an exit ticket or code-lookup drill, used to adjust teaching before the summative evaluation.