Exam Cheat Sheet · Quick Reference

Maryland Master Electrician

Maryland · PSI Services Contractor

Verified, not estimated. Every figure below is drawn from the official exam structure we maintain — question counts, passing standard and topic weighting. Practice questions are grounded in the source law with statute citations. We omit any figure we can't verify rather than guess at it.

Total questions

Passing score

70%

Exam time

240 min

Administered by

PSI Services Contractor

Format

Reference materials allowed

Maryland State Portion 90 questions

Electrical Theory 10 Q · 11%

DefinitionsTheory Including Ohm's LawTechniquesTroubleshootingEquipment/DevicesInstrumentsMaterialsMathConversionsDiagramsSymbols

Wiring and Protection 14 Q · 16%

NEC Article 100NEC Article 110NEC Article 200-210NEC Article 215-225NEC Article 230NEC Article 240NEC Article 250-285

Wiring Methods and Materials 13 Q · 14%

NEC Article 300NEC Article 310-314NEC Article 320-330NEC Article 332-356NEC Article 358-374NEC Article 376-398

Equipment for General Use 9 Q · 10%

NEC Article 400-411NEC Article 422-427NEC Article 430-450NEC Article 455-490

Special Occupancies 8 Q · 9%

NEC Article 500-525NEC Article 530-547NEC Article 550-590

Special Equipment 4 Q · 4%

NEC Article 600-675NEC Article 680-695

Special Communications 2 Q · 2%

NEC Article 700-708NEC Article 720-830

Calculations 30 Q · 33%

Branch-circuit and feeder load calculations for dwelling units (standard and optional methods)Service load calculations including demand factors for multifamily and commercial occupanciesMotor circuit conductor sizing (single motor, multiple motors, and combination loads)Motor branch-circuit short-circuit and ground-fault protective device ratings (Table 430.52)Motor overload protection sizing and trip current percentagesConductor ampacity correction and adjustment factors (ambient temperature, number of conductors)Conduit and raceway fill calculations for conductorsTransformer overcurrent protection sizing (primary and secondary, Tables 450.3(A) and 450.3(B))

Key Distinctions

OverloadvsShort circuit / ground fault

An overload is operation of equipment in excess of normal, full-load rating that causes damage or dangerous overheating when it persists, while a fault such as a short circuit or ground fault is expressly not an overload (both are overcurrent conditions, but they require different protective approaches).

NEC 2020 Article 100 — Definitions, Overload

Surge arrestervsSurge-protective device (SPD)

A surge arrester limits surge voltages by discharging or bypassing surge current and prevents continued flow of follow current while remaining capable of repeating the function, whereas an SPD limits transient voltages by diverting or limiting surge current.

NEC 2020 Article 100 — Definitions, Surge Arrester

Interrupting ratingvsShort-circuit current rating / available fault current

Interrupting rating is the highest current at rated voltage a device is identified to interrupt under standard test conditions; short-circuit current rating is the prospective symmetrical fault current an apparatus can be connected to without damage, and available fault current is the largest current deliverable at a point during a short circuit.

NEC 2020 Article 100 — Definitions, Interrupting Rating

Motor full-load current from NEC tablesvsMotor nameplate current

Per 430.6(A)(1) the NEC full-load current tables (e.g., Table 430.250 for three-phase) are used to size branch-circuit conductors, while the nameplate current is used only for sizing separate motor overload protection per 430.6(A)(2).

NEC 2020 Section 430.6(A)(1)

Continuous-duty motor conductor sizing (430.22(A))vsIntermittent-duty (elevator) motor conductor sizing (Table 430.22(E))

Continuous-duty motors use 125% of the table full-load current, while motors in other than continuous duty (short-time, intermittent, periodic, varying) use the Table 430.22(E) percentages — 140% of nameplate current for intermittent-duty elevator service with a continuous-rated motor.

NEC 2020 Informative Annex D, Example D9; Table 430.22(E)

Transformer 'primary only' protection (≤1000 V)vsTransformer 'primary and secondary' protection (≤1000 V)

For primary currents less than 9 amperes, the primary-only method permits a maximum of 167%, while the primary-and-secondary method permits a maximum primary overcurrent protection of 250% per Table 450.3(B).

NEC 2020 Table 450.3(B)

Annex C standard fill tables (e.g., Table C.1)vsAnnex C (A)-suffix fill tables (e.g., Table C.1(A), C.9(A))

The standard tables apply only to concentric stranded conductors, while the companion (A) tables must be used for compact stranded conductors and are based on Chapter 9, Table 5A rather than Table 5.

NEC 2020 Informative Annex C, Table C.1 Note 1

EMT support spacing (358.30(A))vsFMC support spacing (348.30(A))

EMT must be fastened within 900 mm (3 ft) of each box, cabinet, conduit body or other termination (and at intervals not over 10 ft), while FMC (and AC cable) must be secured within 300 mm (12 in.) of each termination.

NEC 2020 Section 358.30(A)

Article 706 — Energy Storage SystemsvsArticle 480 — Storage Batteries

Article 706 governs ESS with a capacity greater than 3.6 MJ (1 kWh); systems of 3.6 MJ (1 kWh) or less are governed by Article 480.

NEC 2020 Section 706.1

Covered conductorvsInsulated conductor

A covered conductor is encased in material whose composition or thickness is NOT recognized by the Code as electrical insulation, so it cannot be treated as insulated, while an insulated conductor is encased in material that IS recognized as electrical insulation.

NEC 2020 Article 100 — Definitions, Conductor Covered and Conductor Insulated

SwitchboardvsPanelboard

A switchboard is generally accessible from the rear as well as the front and is not intended for installation in cabinets, while a panelboard is accessible only from the front and is designed for assembly in a cabinet.

NEC 2020 Article 100 — Definitions, Switchboard and Panelboard

SwitchgearvsSwitchboard / motor control center

Switchgear is completely enclosed on all sides and top with sheet metal (except ventilating openings and inspection windows) and contains primary power circuit switching or interrupting devices with buses and connections, unlike a switchboard (open to the rear) or a motor control center (principally motor control units).

NEC 2020 Article 100 — Definitions, Switchgear

Voltage to ground on a grounded circuitvsVoltage to ground on an ungrounded circuit

On grounded circuits it is the voltage between the given conductor and the grounded point or conductor, while on ungrounded circuits it is the greatest voltage between the given conductor and any other conductor of the circuit.

NEC 2020 Article 100 — Definitions, Voltage to Ground

Isolating switchvsGeneral-use switch

An isolating switch has no interrupting rating and is intended to be operated only after the circuit has been opened by other means, while a general-use switch is rated in amperes and capable of interrupting its rated current (a motor-circuit switch is rated in horsepower).

NEC 2020 Article 100 — Definitions, Switch Isolating

Key Terms

Ampacity NEC 2020 Article 100 — Definitions

The maximum current, in amperes, that a conductor can carry continuously under the conditions of use without exceeding its temperature rating.

Continuous load NEC 2020 Article 100 — Definitions

A load where the maximum current is expected to continue for 3 hours or more (typically requiring conductors and devices rated at 125% of the continuous load current).

Overcurrent NEC 2020 Article 100 — Definition of Overcurrent

Any current in excess of the rated current of equipment or the ampacity of a conductor, which may result from overload, short circuit, or ground fault.

Overload NEC 2020 Article 100 — Definitions, Overload

Operation of equipment in excess of normal, full-load rating that, when it persists for a sufficient length of time, would cause damage or dangerous overheating; a fault such as a short circuit or ground fault is not an overload.

Fault current / available fault current NEC 2020 Article 100 — Definition of Fault Current

Fault current is the current delivered at a point on the system during a short-circuit condition; available fault current is the largest amount of current capable of being delivered at that point during a short-circuit condition.

Class A GFCI NEC 2020 Article 100 — Definitions, Ground-Fault Circuit Interrupter (GFCI)

A ground-fault circuit interrupter that trips when ground-fault current is 6 mA or higher and does not trip when it is less than 4 mA.

Arc-fault circuit interrupter (AFCI) NEC 2020 Article 100 — Definitions, Arc-Fault Circuit Interrupter (AFCI)

A device intended to provide protection from the effects of arc faults by recognizing characteristics unique to arcing and functioning to deenergize the circuit when an arc fault is detected.

Readily accessible NEC 2020 Article 100 — Definitions, Accessible Readily (Readily Accessible)

Capable of being reached quickly for operation, renewal, or inspection without requiring those needing ready access to use tools (other than keys), climb over or under, remove obstacles, or resort to portable ladders.

In sight from (within sight) NEC 2020 Article 100 — Definitions, In Sight From (Within Sight From, Within Sight)

The specified equipment must be both visible from and not more than 15 m (50 ft) distant from the other equipment; both conditions must be met.

Demand factor NEC 2020 Article 100 — Definitions, Demand Factor

The ratio of the maximum demand of a system, or part of a system, to the total connected load of that system or part under consideration.

Neutral point NEC 2020 Article 100 — Definitions, Neutral Point

The common point on a wye connection in a polyphase system, the midpoint of a single-phase 3-wire system, the midpoint of the single-phase portion of a 3-phase delta system, or the midpoint of a 3-wire dc system; at that point the vectorial sum of the nominal voltages from all other phases using the neutral is zero potential.

Inverse time (circuit breaker) NEC 2020 Article 100 — Definitions, Circuit Breaker (Inverse Time)

A qualifying term indicating that a delay is purposely introduced in the breaker's tripping action, and that delay decreases as the magnitude of the current increases.

Selective coordination NEC 2020 Article 100 — Definitions, Coordination Selective (Selective Coordination)

Localization of an overcurrent condition to restrict outages to the circuit or equipment affected, accomplished by selecting and installing overcurrent protective devices with ratings or settings suited to the full range of available overcurrents (overload to available fault current) and their associated opening times.

Separately derived system NEC 2020 Article 100 — Definitions, Separately Derived System

An electrical source, other than a service, having no direct connection to circuit conductors of any other electrical source other than those established by grounding and bonding connections.

Thermal protector (as applied to motors) NEC 2020 Article 100 — Definitions, Thermal Protector (as applied to motors)

A protective device assembled as an integral part of a motor or motor-compressor that, when properly applied, protects the motor against dangerous overheating due to overload and failure to start; such a motor is 'thermally protected.'

Controller NEC 2020 Article 100 — Definitions, Controller

A device or group of devices that serves to govern, in some predetermined manner, the electric power delivered to the apparatus to which it is connected.

Type 1 SPD NEC 2020 Article 100 — Definitions, Surge-Protective Device (SPD)

A permanently connected surge-protective device intended for installation between the secondary of the service transformer and the line side of the service disconnect overcurrent device (Type 2 is load side of the service disconnect, Type 3 at point of utilization, Type 4 component SPDs).

Uninterruptible power supply (UPS) NEC 2020 Article 100 — Definitions, Uninterruptible Power Supply

A power supply used to provide alternating current power to a load for some period of time in the event of a power failure.

Nonlinear load NEC 2020 Article 100 — Definitions, Nonlinear Load

A load where the wave shape of the steady-state current does not follow the wave shape of the applied voltage.

Copper-clad aluminum conductor NEC 2020 Article 100 — Definitions, Copper-Clad Aluminum Conductors

A conductor drawn from a copper-clad aluminum rod with copper metallurgically bonded to an aluminum core, the copper forming a minimum of 10 percent of the cross-sectional area of a solid conductor or of each strand.

Class I Group B NEC 2020 Section 500.6(A)(2)

A flammable gas or flammable/combustible liquid-produced vapor mixed with air that may burn or explode, having a maximum experimental safe gap (MESG) of 0.45 mm or less or a minimum igniting current (MIC) ratio of 0.40 or less.

Formulas to Know

Minimum feeder conductor ampacity with continuous and noncontinuous load (215.2(A)(1))(continuous load × 125%) + noncontinuous load; e.g., (100 A × 1.25) + 30 A = 155 A

Minimum motor feeder conductor ampacity (430.24)125% of the largest motor FLC + sum of the FLCs of the other motors; e.g., (1.25 × 15.2) + 15.2 + 15.2 = 49.4 A

Branch-circuit conductor ampacity for intermittent-duty (elevator) motor, continuous rated (Table 430.22(E))nameplate current × 140%; e.g., 52 A × 1.40 = 72.8 A (continuous duty instead uses 125% per 430.22(A))

Generator output conductor ampacity (445.13)ampacity ≥ 115% of generator nameplate current; 80 A × 1.15 = 92 A; 200 A × 1.15 = 230 A

Inverse time circuit breaker sizing for a motor (Table 430.52 / 430.52(C)(1) Exc. 2(c))

Max = 250% of motor FLC (single-phase), rounded up to the next standard size if the motor will not start: 50 A × 2.5 = 125 A → next standard size 150 A; absolute ceiling where needed for starting = 400% of FLC for FLC ≤ 100 A: 60 A × 4.00 = 240 A

Motor overload protection maximum (430.32(A)(1))

Separate overload device ≤ 125% × nameplate FLC for motors with a marked service factor ≥ 1.15 or marked temperature rise ≤ 40°C; ≤ 115% × nameplate FLC for all other motors. These are maximums, not a range: 30 A → 37.5 A max (service factor 1.15) or 34.5 A max (other motors)

Dwelling calculated load, Article 220 components

(floor area × 3 VA/sq ft) + (1500 VA × number of 2-wire small-appliance circuits) + (1500 VA × number of laundry circuits); e.g., 2000 sq ft: 6000 + 3000 + 1500 = 10,500 VA; per-unit totals × number of units before demand factors (8100 × 4 = 32,400 VA); dwelling units only: a retail store uses the Table 220.12 unit load, 1.9 VA/sq ft, plus 180 VA per receptacle outlet

Conduit fill check (Chapter 9, Table 1)

Max fill = 40% for 3 or more conductors; conduit area = π r², conductor area = π r² each; fill % = total conductor area ÷ conduit area (e.g., 0.0368 in² ÷ 0.7854 in² ≈ 4.7% < 40%)

Series-parallel DC circuit total current

R(parallel of two) = (R1 × R2)/(R1 + R2) or 1/Rp = Σ1/R; R_total = series R + Rp; I = E / R_total; branch current = (I × Rp) ÷ R_branch (e.g., 36 V ÷ 12 Ω = 3 A; 12 V ÷ 24 Ω = 0.5 A)

Box and pull box sizing rules

Box fill: 2.25 in.³ (36.9 cm³) per 12 AWG conductor; straight pull box length ≥ 8 × the metric designator (trade size) of the largest raceway for conductors 4 AWG or larger

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