MTTC Electrical Trade Test cheat sheet

Qualified person: one who has demonstrated skills and knowledge related to the construction and operation of electrical equipment and installations and has received safety training on the hazards involved.

Approach boundaries (unqualified persons, 600 V class): limited 10 ft, restricted 5 ft, prohibited to the live part; qualified persons use shock-protection boundaries based on voltage and incident energy.

Lockout/tagout order: notify affected workers, identify all energy sources, shut down, isolate, apply locks and tags, release stored energy, verify de-energized with a tester rated for the voltage.

NFPA 70E PPE categories are selected from an incident-energy analysis or tables; arc-rated clothing and equipment must have an arc rating at least equal to the calculated incident energy.

Working space in front of equipment (Table 110.26(A)(1)): 3 ft for 0-150 V to ground, 3 ft for 151-300 V, 3.5 ft for 301-400 V, 4 ft for 401-600 V, measured from the live part.

GFCI protection is required for 125-240 V receptacles in bathrooms, garages, outdoors, kitchens, laundry areas, basements, and within 6 ft of sinks, per Article 210.

Bonding jumpers around water meters and at service equipment must be sized from Table 250.102(C)(1); equipment grounding conductors from Table 250.122 based on the overcurrent device rating.

A circuit is de-energized only after a voltage test with a meter proved functional before and after the test; treat conductors as energized until tested.

Ohm's law: E = I x R; power P = E x I = I^2 x R = E^2 / R. In a series circuit, current is common and voltage divides; in parallel, voltage is common and current divides.

Three-phase power: P = sqrt(3) x E_line x I_line x power factor; apparent power S (VA) = sqrt(3) x E x I; reactive power Q = sqrt(S^2 - P^2).

Impedance Z = sqrt(R^2 + (X_L - X_C)^2); inductive reactance X_L = 2 x pi x f x L; capacitive reactance X_C = 1 / (2 x pi x f x C).

Transformer turns ratio: E_primary / E_secondary = N_primary / N_secondary = I_secondary / I_primary; a step-down voltage means step-up current.

Induced EMF in a conductor: e = B x l x v (flux density x length x velocity), with direction given by the right-hand rule; generator action requires relative motion between conductor and field.

Conductor resistance rises with temperature and length, and falls with cross-sectional area: R = (K x L) / CM, where CM is circular mils and K is the resistivity constant.

Motor synchronous speed: N_s = (120 x f) / P; percent slip = (N_s - N_r) / N_s x 100. A 4-pole motor on 60 Hz has N_s = 1800 rpm.

Effective (RMS) value of a sine wave = 0.707 x peak; average value = 0.637 x peak; peak = 1.414 x RMS.

NM-B cable may not be installed in wet locations, in masonry cavities, in raceways outdoors, or where subject to physical damage; it requires protection where passing through framing within 1-1/4 in of the surface.

MC cable and AC cable each need listed connectors; AC cable's armor serves as the equipment grounding path via the bonding strip, while MC cable requires a separate green grounding conductor.

Box fill (Article 314.16): count each current-carrying conductor as 1, each clamp as 1, each device as 2 (yoke), each grounding conductor as 1; multiply by the volume per conductor from Table 314.16(B).

Support intervals: NM cable every 4.5 ft and within 12 in of boxes; EMT every 10 ft with a support within 3 ft of each box; rigid metal conduit every 10 ft; PVC schedule 40 every 3 ft for smaller sizes per Table 352.30.

Bending radius for raceways: one-shot bends must not kink or flatten; minimum radius for EMT is 2.5 times the trade size for 1/2 in and 3/4 in, per Table 344.24/358.24.

Conductor ampacity adjustments: Table 310.15(C)(1) applies when more than three current-carrying conductors share a raceway; 4-6 conductors = 80%, 7-9 = 70%, 10-20 = 50%.

Ambient temperature correction factors from Table 310.15(B)(1) reduce ampacity in hot locations; the ampacity used is the lower of the corrected value and the termination rating.

Receptacle outlets on a 20 A small-appliance branch circuit must be grounded; kitchen countertop receptacles require GFCI and no more than 4 ft from a point along the wall to a receptacle.

Conduit fill (Chapter 9): one conductor 53%, two conductors 31%, over two 40% of the raceway's internal cross-sectional area; use Annex C for exact counts by conductor type and size.

Conductor insulation ratings: THHN/THWN-2 is 90 C dry, 75 C wet; ampacity must be taken from the 75 C column for terminations rated 75 C unless the equipment is listed otherwise.

Voltage drop: VD = (2 x K x I x L) / CM for single-phase, and (sqrt(3) x K x I x L) / CM for three-phase, where K is about 12.9 for copper and 21.2 for aluminum.

Cable tray and busway fill, plus raceway nipples 24 in or less, permit a 60% fill; nipples may also allow reduced conductor sizing per 310.14(A)(2).

Conductors in parallel must be the same length, same conductor material, same insulation type, and terminated to the same equipment; minimum size is 1/0 AWG in most cases.

Expansion fittings are required where raceways cross building expansion joints and where straight runs exceed temperature-change limits; PVC needs expansion couplings per 352.44.

Cable supports for Type SE and USE service-entrance cable: within 12 in of boxes and every 4.5 ft; direct-burial conductors need 24 in cover for 0-600 V unless under a 2 in concrete slab.

Raceway sealing: conduit entering a building from a hazardous location or from outdoors must be sealed per 300.5(G) and 501.15 to prevent gas or moisture migration.

Standard branch-circuit ratings: 15, 20, 30, 40, 50, 60 A; small-appliance and laundry circuits must be 20 A, and at least two small-appliance circuits are required in a dwelling kitchen.

Continuous loads are calculated at 125% for branch circuits and feeders; the overcurrent device must be at least 125% of the continuous load plus 100% of the noncontinuous load.

Service calculation (dwelling, optional method): general lighting 3 VA per square foot, small appliance and laundry circuits at 1500 VA each, then apply the Table 220.42 demand factors.

Demand factors for ranges and dryers come from Table 220.55; a single 12 kW range may be calculated at 8 kW demand.

Feeder and service conductor sizing uses the calculated load, not the panel bus rating; the service disconnect must be rated at least the calculated load and the panel rating must not be exceeded.

Ampacity of service-entrance conductors must be at least 83% of the service rating for a set of conductors where the load calculation permits; the grounded conductor may be reduced per 220.61.

A feeder tap not exceeding 10 ft may use conductors sized at least 1/10 of the overcurrent device, protected from physical damage, and terminating in a single device.

Panelboard: 42-circuit maximum for a lighting and appliance branch-circuit panelboard unless listed otherwise; unused openings must be closed, and the panel needs a working space of 30 in wide by 36 in deep.

Motor branch-circuit conductor ampacity is at least 125% of the motor full-load current from Tables 430.248-430.250; overload protection is sized from the nameplate service factor and temperature rise.

Short-circuit and ground-fault protection for a standard motor uses Table 430.52: inverse-time breaker up to 250% of FLC, dual-element fuse up to 175%, nontime-delay fuse up to 300%.

Motor disconnecting means must be within sight of the motor and controller, or capable of being locked open; the disconnect must be rated at least 115% of the motor FLC.

A motor controller must have a horsepower rating not less than the motor it controls; a manual starter is limited to motors of 2 hp or less at 300 V or below.

Three-phase motor reversal: swap any two of the three line leads at the motor terminals or at the starter; a phase monitor or rotation meter confirms A-B-C sequence before energizing.

Transformer protection: primary-only protection may be up to 125% of primary FLC for transformers over 1000 V, and Table 450.3(B) governs 600 V and below; secondary conductors must be protected at their ampacity.

Wye-delta and part-winding starters reduce starting current; reduced-voltage starters lower inrush but also lower starting torque by the square of the voltage reduction.

VFD cable should be shielded and the motor grounded per the drive manual; long motor leads require load reactors or filters to limit reflected-wave voltage stress on the winding.

System grounding: the service neutral is bonded to the enclosure and grounding electrode conductor at one point only; downstream panels use a separate ground bar and isolated neutral.

Grounding electrode conductor sizing comes from Table 250.66 and is based on the largest ungrounded service conductor; it never needs to be larger than 3/0 copper or 250 kcmil aluminum.

Equipment grounding conductor sizing comes from Table 250.122 and is based on the rating of the overcurrent device protecting the circuit, not the conductor ampacity.

Overcurrent devices must be sized to carry the load and must not exceed the ampacity of the conductors they protect, except for the specific allowances for motor circuits, taps, and air-conditioning equipment.

Breaker series ratings: a lower-rated breaker may be used on a system with higher available fault current only if it is listed and marked for use with the upstream device.

Fuse classes: RK1 and RK5 are current-limiting and rejection-type; Class J is current-limiting with the smallest footprint; Class T is fast-acting for high fault currents.

Ground-fault protection of equipment (GFPE) at 480Y/277 V services rated 1000 A or more is required per 230.95, with a maximum setting of 1200 A and a time delay.

Bonding of metal water piping, structural steel, and gas piping (where required by local code) must be done with listed clamps; the bonding jumper for a water pipe is sized from Table 250.102(C)(1).

Insulation resistance test: apply a DC voltage for 1 minute and record megohms; a reading below 1 megohm per 1000 V of applied test voltage, or below 1 megohm, indicates a problem.

Continuity testing requires the circuit to be de-energized; a low-resistance ohmmeter verifies grounding paths and switch contacts, and readings above 1 ohm on a grounding path warrant investigation.

Voltage measurements: line-to-line on a 120/208 V wye system reads 208 V, line-to-neutral reads 120 V; a missing neutral shows normal line-to-line but unbalanced or zero line-to-neutral values.

Clamp-on ammeter readings on a three-phase motor should be balanced within a few percent; a large imbalance suggests a winding fault, single-phasing, or a loose connection.

Motor winding resistance test: measure each winding to ground and phase-to-phase; a shorted turn shows low or zero resistance, an open winding reads infinite, and a grounded winding reads low to ground.

Thermography and torque checks are preventive maintenance tasks; loose terminations show as hot spots under load and are a leading cause of failures.

Ground-fault location: a clamp meter around the phase and neutral together reads zero in a healthy circuit; any residual current indicates leakage to ground.

Phase rotation and motor direction are verified with a rotation meter before coupling a driven load, preventing damage from reversed rotation.

Learning objectives should be written with observable action verbs (calculate, size, identify, demonstrate) tied to the trade task, not vague verbs such as know or understand.

Lesson plan sequence: state objective, activate prior knowledge, demonstrate the skill, guided practice, independent practice, and formative check before summative assessment.

Hands-on safety instruction should use a task analysis with each step listed and hazard controls identified; learners are evaluated against the checklist before working live or near energized equipment.

Formative assessment examples in electrical training include quick practical checks, exit tickets on Ohm's law, and code-lookup drills scored against the referenced article.

Assessment validity requires that the test measures the stated objective; a written quiz cannot certify conduit-bending skill, which needs a performance assessment with a rubric.

Rubrics for electrical labs should separate safety compliance, code accuracy, workmanship, and troubleshooting logic so scores give diagnostic feedback.

Differentiation for mixed-experience classes: pair apprentices with experienced helpers on complex tasks, provide code tables as scaffolds, and offer extension problems on load calculations.

Feedback should be specific and timely, referencing the code article or measurement error, so learners can correct the procedure on the next attempt.