MT Journeyman Electrician cheat sheet

Ohm's law: E = I × R; power: P = E × I = I²R = E²/R. For three-phase, P = √3 × E_line × I_line × PF.

Ampacity adjustment for ambient temperature uses Table 310.15(B)(1); for more than three current-carrying conductors in a raceway or cable, use Table 310.15(C)(1).

Voltage drop approximation for single-phase: VD = 2 × K × I × L / CM; three-phase: VD = √3 × K × I × L / CM, where K ≈ 12.9 for copper, 21.2 for aluminum.

Conductor resistance changes with temperature: R2 = R1 × [1 + α(T2 − 25)], α ≈ 0.00323/°C for copper at 25°C reference.

Series circuit: same current through all elements; total resistance is sum. Parallel circuit: same voltage across branches; total conductance is sum of branch conductances.

Power factor correction capacitor kVAR = P × (tan θ1 − tan θ2), where θ1 and θ2 are the initial and target power-factor angles.

A balanced three-phase wye system: line voltage = √3 × phase voltage; line current = phase current. Delta: line current = √3 × phase current; line voltage = phase voltage.

The grounded conductor (neutral) carries only unbalanced current in a balanced multiwire circuit; in a 120/240 V single-phase three-wire system, the neutral carries the difference of the two ungrounded conductor currents.

NM-B cable is permitted only in normally dry locations; it must be protected where subject to physical damage and cannot be embedded in masonry or concrete.

Type AC cable and Type MC cable differ: AC cable has a bare aluminum bonding strip in intimate contact with the armor; MC cable armor is not suitable as an equipment grounding conductor unless listed and identified for that use.

RMC requires support within 3 ft of each box and at intervals not exceeding 10 ft. IMC support intervals are the same; EMT requires support within 3 ft and at intervals not exceeding 10 ft, with additional rules for specific lengths.

Liquidtight flexible metal conduit (LFMC) requires a separate equipment grounding conductor when used in corrosive areas or where flexibility is needed; the conduit itself may serve as EGC only if listed and terminated with listed fittings.

The number of conductors permitted in a raceway is limited by Table 1 of Chapter 9; conduit fill for over two conductors is 40% of the raceway internal cross-sectional area.

Box fill calculations per NEC 314.16(B): each current-carrying conductor counts as one volume allowance; each device yoke counts as two; each grounding conductor counts as one; each cable clamp counts as one.

The minimum burial depth for direct-buried conductors depends on the wiring method and voltage: 24 in. for direct-buried cable or conduit under a building or street; 18 in. for direct-buried cable or conduit in other areas; 12 in. for residential branch circuits rated 120 V or less with GFCI protection and maximum 20 A.

Expansion fittings are required for raceways where significant temperature changes occur, such as exposed runs on rooftops; the fitting must accommodate the calculated expansion of the raceway material.

Conductors in parallel must be the same length, same conductor material, same circular mil area, same insulation type, and terminated in the same manner; the minimum size is 1/0 AWG for general use.

The service neutral (grounded conductor) must be bonded to the equipment grounding conductor at the service disconnecting means only; downstream panels must have separate neutral and ground buses.

The grounding electrode system must include a metal underground water pipe in direct contact with the earth for 10 ft or more, a concrete-encased electrode, and a ground ring, where available; supplementary electrodes may be added.

The equipment grounding conductor for a feeder is sized per Table 250.122 based on the rating of the overcurrent device protecting the feeder.

Standard overcurrent device ratings are 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300, 350, 400, 450, 500, 600, 700, 800, 1000, 1200, 1600, 2000, 2500, 3000, 4000, 5000, 6000 A.

The next higher standard overcurrent device rating is permitted for branch circuits and feeders only when the conductor ampacity does not exceed 800 A and the next higher rating does not exceed 800 A, and the ampacity is not less than the load.

For a 120/240 V single-phase service, the minimum service disconnecting means rating is 100 A for a one-family dwelling; the service conductors must be sized for the calculated load and the neutral may be reduced per 220.61.

Ground-fault protection of equipment (GFPE) is required for solidly grounded wye services of more than 150 V to ground but not exceeding 600 V phase-to-phase, with a disconnect rating of 1000 A or more; the setting must not exceed 1200 A and must have a delay.

Bonding jumpers around water meters, gas piping, and other metallic piping systems must be sized per Table 250.102(C)(1) based on the largest ungrounded service conductor.

The maximum allowable ground-fault return path impedance must be low enough to ensure the overcurrent device opens; equipment grounding conductors must be continuous and not rely on conduit fittings alone unless listed.

Dwelling unit general lighting load: 3 VA per square foot; small-appliance and laundry branch circuits: 1500 VA each; the neutral load is subject to the 220.61 demand factors.

Standard method for dwelling unit service calculation: add general lighting, small-appliance, laundry, and all other loads; apply demand factors from Table 220.42; add the largest of the heating or cooling load; add 25% of the largest motor.

Optional method for dwelling units per 220.82: total general load (3 VA/ft² plus 1500 VA per small-appliance and laundry circuit plus nameplate ratings of all appliances) is subject to a 100% demand factor for the first 10 kVA and 40% for the remainder.

For a single-family dwelling, the minimum number of 20 A small-appliance branch circuits is two; laundry requires one 20 A circuit; bathroom receptacle outlets require at least one 20 A circuit.

Receptacle outlet spacing in dwelling units: no point on a wall space is more than 6 ft from a receptacle; wall spaces wider than 2 ft require a receptacle; kitchen countertop receptacles must be spaced so no point is more than 24 in. from a receptacle.

Voltage drop for branch circuits and feeders should not exceed 3% for branch circuits and 5% total for branch circuit plus feeder; these are recommended limits in NEC 210.19(A) informational note and 215.2(A) informational note.

Feeder conductor sizing: the feeder ampacity must be at least 125% of the continuous load plus 100% of the noncontinuous load before applying adjustment or correction factors.

The minimum size of service-entrance conductors for a one-family dwelling is 100 A; for a two-family dwelling, each unit must have a minimum 100 A service or a single service sized for the calculated load.

For a 120/240 V single-phase service, the neutral conductor may be reduced to the larger of the unbalanced load or the minimum size permitted by 250.24(C) for the grounding electrode conductor.

Motor branch-circuit short-circuit and ground-fault protection: use Table 430.52; for a standard inverse-time circuit breaker, the maximum rating is 250% of the motor full-load current; for a dual-element fuse, 175%.

Motor overload protection is sized per 430.32: for a motor with a marked service factor of 1.15 or more, the overload device must be sized at no more than 125% of the motor nameplate full-load current.

Motor conductor ampacity must be at least 125% of the motor full-load current from Table 430.250 for the motor horsepower and voltage.

The disconnecting means for a motor must be located within sight of the motor and must be capable of being locked in the open position; the disconnect rating must be at least 115% of the motor full-load current.

For a hermetic refrigerant motor-compressor, the branch-circuit conductor ampacity must be at least 125% of the rated-load current, and the short-circuit and ground-fault protection must not exceed the marked maximum.

A contactor is a magnetically operated switch used for controlling motors; an overload relay provides running overload protection and must be selected based on the motor nameplate current and service factor.

The motor control circuit is a circuit that carries the electric signals directing the performance of the controller; it is not the main power circuit. Control transformers must be protected per Article 430, Part VI.

For a motor supplied by a variable-frequency drive, the conductor sizing and overcurrent protection are based on the drive input current, and the drive must be listed for the application.

Class I locations are those in which flammable gases or vapors are or may be present; Division 1 vs. Division 2 depends on the likelihood of the hazard being present during normal operations.

Class II locations involve combustible dust; Class III locations involve easily ignitable fibers or flyings. Equipment must be marked with the appropriate class, division, and group.

In hazardous (classified) locations, seals are required in conduit systems to prevent the passage of gases or vapors; the seal fitting must be located within 18 in. of the enclosure for Class I, Division 1.

Bathroom receptacle outlets must be GFCI protected; all 125 V, single-phase, 15- and 20-A receptacles in dwelling unit bathrooms must have GFCI protection.

Swimming pool underwater luminaires must be GFCI protected and must be installed with a listed pool niche; the forming shell must be bonded to the pool bonding grid.

For a health care facility, essential electrical systems must be separated into critical, life safety, and equipment branches; the transfer switch must be configured to ensure continuity of power.

In a commercial garage, each branch circuit supplying receptacles for portable equipment must have GFCI protection if the receptacle is within 18 in. of the floor.

For a mobile home, the service must be a 120/240 V single-phase, three-wire system; the feeder must be sized per Article 550 and the grounding electrode conductor must be sized per 550.16.

Box fill calculation per NEC 314.16: count each conductor that terminates in the box, each conductor that passes through without termination, and each device yoke (two conductors) and grounding conductor (one conductor).

The volume allowance per conductor depends on the conductor size: 14 AWG = 2.0 in³, 12 AWG = 2.25 in³, 10 AWG = 2.5 in³, 8 AWG = 3.0 in³, 6 AWG = 5.0 in³.

The minimum size of a box for a given number of conductors is found by multiplying the number of volume allowances by the cubic inch allowance for the largest conductor.

Raceway fill: for one conductor, 53% of the raceway internal area; for two conductors, 31%; for over two conductors, 40%. These percentages are from Chapter 9, Table 1.

The number of conductors in a raceway is limited by the raceway size and the conductor insulation thickness; use Annex C tables for quick reference.

Boxes must be supported; a box must be rigidly supported unless it is a listed box that is supported by the raceway. The maximum support spacing for raceways is 10 ft for RMC, IMC, and EMT.

Conductors in a raceway must be protected from abrasion; bushings or listed fittings are required where conductors enter a box or enclosure.

The minimum bending radius of a raceway is specified in Chapter 9, Table 2; for a 1-in. EMT, the minimum radius is 5.75 in. for a field bend.

The maximum number of quarter bends (90° bends) between pull points in a raceway is four; this includes offsets and other bends that are not pulls.

Montana electrical licensing is administered by the Montana Board of Electrical Examiners within the Department of Labor and Industry; the board adopts rules that reference the NEC.

A journeyman electrician license in Montana requires a combination of documented work experience and passing a written examination; the specific hour requirements and application procedures are set by board rule.

Montana law requires that electrical work be performed by licensed electricians or under the supervision of a licensed electrician, with limited exceptions for homeowners working on their own residence.

Continuing education is required for license renewal in Montana; the number of hours and the approved subject areas are specified by the board.

A contractor's license is required for anyone engaged in the business of electrical contracting in Montana; the contractor must employ a licensed master or journeyman electrician.

The Montana Electrical Code is the NEC as adopted by the board, with any amendments published in the Administrative Rules of Montana (ARM).

Violations of Montana electrical licensing laws can result in fines, license suspension, or revocation; the board has authority to investigate complaints and hold hearings.

License reciprocity in Montana is limited; applicants from other states must meet Montana requirements and may be required to pass the Montana examination.

NFPA 70E requires an arc flash risk assessment to determine the incident energy and the arc flash boundary; the assessment must be updated when a major modification or renovation occurs.

The arc flash boundary is the distance at which a person without arc-rated clothing could receive a second-degree burn; it is calculated from the incident energy and the working distance.

PPE categories: arc-rated clothing and equipment must have an arc rating at least equal to the incident energy; the arc rating is expressed in cal/cm².

The shock approach boundaries are limited, restricted, and prohibited; the limited approach boundary for a 480 V system is 10 ft, and the restricted approach boundary is 1 ft.

Lockout/tagout procedures must be followed before working on or near energized equipment; the equipment must be de-energized and verified absent of voltage, unless justified as infeasible and approved.

A job hazard analysis should be performed before starting work; it identifies hazards, required PPE, and emergency procedures.

Test instruments must be rated for the voltage and category of the circuit being tested; a CAT III meter is required for distribution-level measurements.

Working alone on energized equipment is prohibited for voltages above 600 V; a second person must be present to provide assistance in case of emergency.