Exam Cheat Sheet · Quick Reference
ICC T18 Residential Electrician Exam (2020 NEC)
National · Pearson Vue
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
60
Passing score
70%
Exam time
180 min
Administered by
Pearson Vue
Format
Reference materials allowed
National State Portion 60 questions
General Knowledge
7 Q · 12%
Electrical Theory and General Electrical Load CalculationsCode Definitions and TermsNEC Purpose, Scope, and Code Arrangement (Article 90)General Requirements for Electrical Installations (Article 110)Working Spaces and Clearances Around Electrical EquipmentConductor Properties, Ratings, and ConnectionsGrounded Conductor Identification and Neutral Load CalculationsOhm's Law, Series, Parallel, and Combination Circuit AnalysisAC Power Calculations: Watts, kW, kVA, Horsepower, Power Factor, and ImpedanceElectrical Symbols, Field Terms vs. NEC Terms, and Wiring Diagrams
Services and Service Equipment
13 Q · 22%
Service Load CalculationsService Equipment & Service ConductorsSystem Grounding and BondingService Disconnecting Means RequirementsService Overcurrent ProtectionGrounding Electrode System and Electrode TypesGrounding Electrode Conductor Sizing and InstallationEquipment Grounding Conductor Types and SizingDemand Factors for Dwelling Unit Appliances and Cooking EquipmentOverhead and Underground Service Conductor Requirements
Feeders
8 Q · 13%
Load CalculationsEquipment GroundingFeeder conductor ampacity and minimum size requirements (Article 215)Overcurrent protection for feedersFeeder neutral load calculations (Section 220.61)Optional feeder load calculations for dwelling units (Section 220.82)Demand factors for cooking appliances, clothes dryers, and kitchen equipmentOutside feeder clearances, disconnecting means, and wiring methods (Article 225)Feeder conductor identification (grounded, equipment grounding, and ungrounded conductors)
Branch Circuits and Conductors
15 Q · 25%
Branch Circuit CalculationsRequired Outlets & GFCI/AFCI ProtectionOvercurrent ProtectionEquipment GroundingConductorsConductor Identification (Grounded, Ungrounded, and EGC Color Coding)Ampacity Correction and Adjustment Factors (Temperature and Bundling)Voltage Drop Calculations for Branch CircuitsConductor Insulation Types and Application Provisions (THHN, THWN, RHW, XHHW, etc.)Multiwire Branch Circuit RequirementsBranch-Circuit Voltage Limitations by OccupancyConduit Fill Calculations Using Chapter 9 Tables
+1 more
Wiring Methods and Materials
8 Q · 13%
Raceway InstallationsBoxes and EnclosuresFlexible Cords and CablesCable wiring methods (NM, MC, SE, USE, UF) — uses permitted and not permittedConduit fill calculations and conductor count tables (Chapter 9 Table 1 and Annex C)Underground installation requirements and minimum cover depths (Table 300.5)Protection of cables and raceways from physical damage (NEC 300.4)Conduit bending — 90° stubs, offsets, saddle bends, and back-to-back bendsSecuring and supporting requirements for conduit and cable wiring methodsConductors in raceways — same-circuit grouping, continuity, and splicing rules
Equipment and Devices
5 Q · 8%
LuminairesReceptacles, Switches and Other DevicesAppliances and Other EquipmentLuminaire installation in specific locations (wet, damp, closets, bathtub/shower areas)Recessed luminaire clearances and thermal protection (Type IC vs. non-Type IC)Lighting track installation requirements and prohibited locationsLow-voltage lighting system components, listing, and secondary circuit requirementsSwitch ratings, types, and load control limitations (AC snap, dimmer, electronic control)Grounding of switches, receptacles, and luminairesAppliance disconnecting means requirementsNEMA receptacle and attachment plug configurations and ratings
Special Occupancies, Equipment, and Conditions
4 Q · 7%
Swimming Pools and Similar InstallationsLow Voltage Circuits, Alarm & Similar SystemsGFCI Requirements for Pools, Spas, and Hot TubsEquipotential Bonding for Pool Structures and EquipmentUnderwater Luminaires and Junction Box RequirementsReceptacle and Lighting Clearance Distances from WaterFire Alarm Circuit Power Sources and Wiring Methods (NPLFA and PLFA)Class 1, Class 2, and Class 3 Circuit Classifications and Power Source RequirementsAntenna Systems Grounding and Bonding for Radio and Television EquipmentCommunications Cable Types, Listings, and Installation Applications
Key Distinctions
Surge arrestervsSPD (surge-protective device)
Per Article 100, a surge arrester limits surge voltages by discharging or bypassing surge current and prevents continued flow of follow current while remaining capable of repeating these functions, whereas an SPD limits transient voltages by diverting or limiting surge current.
NEC 2020 Article 100 — Definitions, Surge ArresterInvertervsRectifier
Per Article 100, an inverter is equipment that changes dc to ac, while a rectifier performs the opposite function (ac to dc); a transformer changes voltage levels within the same current type and a dc-to-dc converter changes dc voltage/current levels.
NEC 2020 Article 100 — Definitions, InverterGrounded (neutral) conductor color, 120/240-V single-phase three-wirevsUngrounded conductor colors, 120/240-V single-phase three-wire
The grounded neutral is white or gray (NEC 200.6(A)), while line one ungrounded is black and line two ungrounded is red.
Ugly's Electrical References, 2023 ed., Common Electrical Distribution Systems, Page 13 (2020 ed.: Common Electrical Distribution Systems)120/240-V three-phase four-wire delta high-leg systemvs120/240-V single-phase three-wire system
The delta high-leg (4-wire delta with the midpoint of one phase winding grounded) has a B phase/higher-voltage-to-ground conductor that must be durably and permanently marked orange or tagged per NEC 110.15, which the single-phase three-wire system does not have.
Ugly's Electrical References, 2023 ed., Common Electrical Distribution Systems, Page 13 (2020 ed.: Common Electrical Distribution Systems)225.39(C) one-family dwelling feeder disconnectvs225.39(D) 'all others' feeder/branch-circuit disconnect
For a one-family dwelling the feeder disconnecting means shall be rated not less than 100 amperes, 3-wire, while all installations other than one-circuit, two-circuit, or the one-family dwelling disconnect must be rated not less than 60 amperes.
NEC 2020 Section 225.39(C)225.39(B) two-circuit installation disconnectvs225.39(D) 'all others' disconnect
For installations of not more than two 2-wire branch circuits the disconnecting means must be rated not less than 30 amperes, versus not less than 60 amperes for all other installations.
NEC 2020 Section 225.39(B)220.82(B) optional dwelling unit calculationvs220.83(A) existing dwelling calculation (no added A/C or electric space heating)
The optional dwelling calculation takes 100% of the first 10 kVA plus 40% of the remainder, while the existing-dwelling additional-load calculation with no added air-conditioning or electric space-heating equipment takes 100% of the first 8 kVA plus 40% of the remainder.
NEC 2020 Section 220.82(B)Straight pull box sizing, 314.28(A)(1)vsAngle pull box sizing, 314.28(A)(2)
For straight pulls with 4 AWG or larger conductors the box length shall not be less than 8 times the trade size of the largest raceway; for angle pulls the distance to the opposite wall shall not be less than 6 times the trade size of the largest raceway plus the sum of the diameters of all other raceway entries on the same wall.
NEC 2020 Section 314.28(A)(1)Ampacity adjustment for 7–9 current-carrying conductorsvsAmpacity adjustment for 10–20 current-carrying conductors
Table 310.15(C)(1) requires 70 percent of the table ampacity for 7 to 9 current-carrying conductors in a raceway or cable and 50 percent for 10 to 20 current-carrying conductors.
NEC 2020 Table 310.15(C)(1)GFCI protection at dwelling kitchen countertop receptaclesvsAFCI protection at dwelling kitchen outlets
NEC 210.8(A)(6) requires GFCI protection for dwelling kitchen receptacles serving countertop surfaces, while 210.12(A) separately requires AFCI protection for all 120-volt, single-phase, 15- and 20-ampere branch circuits supplying outlets in dwelling unit kitchens — both are required.
NEC 2020 Section 210.8(A)(6) and 210.12(A)Minimum conductor size, coppervsMinimum conductor size, aluminum or copper-clad aluminum
For voltage ratings up to and including 2000 volts the minimum size is 14 AWG copper versus 12 AWG aluminum or copper-clad aluminum, except as permitted elsewhere in the Code.
NEC 2020 Section 310.3(A)Installations covered by the NECvsInstallations not covered (Article 90.2)
The Code does not cover ships, watercraft other than floating buildings, railway rolling stock, aircraft, or automotive vehicles, but it does cover mobile homes and recreational vehicles.
NEC 2020 Section 90.2(B)(1)Key Terms
Continuous load (Article 100) NEC 2020 Article 100
A load where the maximum current is expected to continue for 3 hours or more; conductors and overcurrent devices for such loads are typically rated at 125% of the continuous load current.
Surge arrester (Article 100) NEC 2020 Article 100 — Definitions, Surge Arrester
A protective device for limiting surge voltages by discharging or bypassing surge current that also prevents continued flow of follow current while remaining capable of repeating these functions.
Inverter (Article 100) NEC 2020 Article 100 — Definitions, Inverter
Equipment that changes dc to ac.
Authority having jurisdiction (Article 90.4) NEC 2020 Section 90.4
The AHJ for enforcement of the Code has responsibility for making interpretations of the rules, deciding on approval of equipment and materials, and granting special permission contemplated in the rules.
Small-appliance branch circuits (210.11(C)(1)) NEC 2020 Section 210.11(C)(1)
Two or more 20-ampere small-appliance branch circuits must be provided in a dwelling unit for all receptacle outlets specified by 210.52(B), in addition to other required branch circuits.
Range branch-circuit minimum (210.19(A)(3)) NEC 2020 Section 210.19(A)(3)
For dwelling units, household electric ranges rated 8¾ kW or more require a minimum branch-circuit rating of 40 amperes.
Building/structure disconnect grouping (225.33(A)) NEC 2020 Section 225.33(A)
The disconnecting means for each supply to a building or structure shall consist of not more than six switches or six circuit breakers in a single enclosure, a group of separate enclosures, or in/on a switchboard or switchgear.
Overhead span clearance (225.18(1)) NEC 2020 Section 225.18(1)
Overhead spans of open conductors not over 1000 volts nominal must have a clearance of not less than 3.0 m (10 ft) above finished grade where the voltage does not exceed 150 volts to ground and the area is accessible to pedestrians only; vegetation such as trees shall not be used to support overhead conductor spans (225.26).
High-impedance grounded neutral system (250.36) NEC 2020 Section 250.36
A system in which a grounding impedance limits ground-fault current to a low value; permitted for 3-phase ac systems of 480 volts to 1000 volts provided all specified conditions are met.
Grounded conductor at a separate building (250.32(B)(1)) NEC 2020 Section 250.32(B)(1)
An equipment grounding conductor must be run with the supply conductors and connected to the building disconnecting means and grounding electrode(s); any installed grounded conductor shall not be connected to the equipment grounding conductor or grounding electrode(s) at the separate building or structure.
Grounding electrode conductor cap for rod, pipe, or plate electrodes (250.66(A)) NEC 2020 Section 250.66(A)
Where connected solely to rod, pipe, or plate electrode(s) and not extending to other electrodes requiring a larger conductor, the grounding electrode conductor is not required to be larger than 6 AWG copper or 4 AWG aluminum.
Common grounding electrode conductor for multiple separately derived systems (250.30(A)(6)(a)(1)) NEC 2020 Section 250.30(A)(6)(a)(1)
A common grounding electrode conductor of the wire type shall not be smaller than 3/0 AWG copper or 250 kcmil aluminum.
Parallel conductors (310.10(G)(1)) NEC 2020 Section 310.10(G)(1)
Aluminum, copper-clad aluminum, or copper conductors for each phase, polarity, neutral, or grounded circuit are permitted to be connected in parallel only in sizes 1/0 AWG and larger; where service-entrance conductors are paralleled in two or more raceways, the grounded conductor in each raceway shall not be smaller than 1/0 AWG (250.24(C)(2)).
Type NM cable bending radius (334.24) NEC 2020 Section 334.24
The radius of the curve of the inner edge of any bend during or after installation of Type NM and NMC cable shall not be less than five times the diameter of the cable.
Type S flexible cord (Table 400.4) NEC 2020 Table 400.4
A 600V hard-service cord with thermoset insulation and thermoset outer covering, suitable for pendant or portable use in damp locations with an extra-hard-usage rating.
Box fill volume allowance, 12 AWG (Table 314.16(B)) NEC 2020 Table 314.16(B)
Each 12 AWG conductor requires a volume allowance of 2.25 in.³ (36.9 cm³); round boxes shall not be used where conduits or connectors requiring locknuts or bushings connect to the side of the box (314.2).
Formulas to Know
Ohm's Law (voltage, current, resistance)
E = I × R; I = E ÷ R (Amperes = Watts ÷ Volts when power is known); R = E ÷ I — e.g., 240 V ÷ 8 A = 30 Ω; 10 A × 12 Ω = 120 V; 1500 W ÷ 120 V = 12.5 AOhm's Law power formulas
P = E × I (volts × amperes = watts); P = E² ÷ R — e.g., 240² ÷ 20 Ω = 2,880 W; R = E² ÷ P — e.g., 120² ÷ 1200 W = 12 ΩSeries and series-parallel resistance / total current
Series: total current is the same in every part (IT = I1 = I2 = I3) and resistances add; two parallel resistors: R = (R1 × R2) ÷ (R1 + R2) (two equal resistors in parallel = R ÷ 2); total I = E ÷ R_total — e.g., 3 + [(8×24)/(8+24)] + 5 = 14 Ω, 28 V ÷ 14 Ω = 2 AMinimum feeder conductor ampacity with continuous load (NEC 2026: 215.4(A)(1); NEC 2023: 215.2(A)(1))
(continuous load × 125%) + noncontinuous load — e.g., (100 A × 1.25) + 30 A = 155 ASingle-phase voltage drop
VD = (2 × K × I × L) ÷ CM, with K = 12.9 for copper and the factor 2 for the out-and-back length — e.g., (2 × 12.9 × 16 A × 60 ft) ÷ 6,530 cmil = 3.79 V (3.79 ÷ 120 ≈ 3.2%)Maximum one-way length for an allowable voltage drop
Allowable VD = V × 0.03 for a 3% limit; L = (VD × CM) ÷ (2 × K × I) — e.g., (7.2 V × 16,510 cmil) ÷ (2 × 12.9 × 40 A) = 115 ft one-wayDwelling general load (Article 220 standard components)
(floor area sq ft × 3 VA/sq ft) + (1,500 VA × number of small-appliance circuits) + (1,500 VA × number of laundry circuits) — e.g., 2,000 sq ft: 6,000 + 3,000 + 1,500 = 10,500 VA; per-unit totals are multiplied by the number of units before demand factorsOptional dwelling unit calculation, general load (220.82(B))
Not less than 100% of the first 10 kVA + 40% of the remainder — e.g., 35 kVA total: 10,000 VA + (40% × 25,000) = 20,000 VA, with the 220.82(C) heating/cooling load added separatelyExisting dwelling additional-load calculation (220.83(A), no added A/C or electric space heating)
100% of the first 8 kVA of existing plus new load + 40% of the remainderFeeder/service neutral (unbalanced) load percentages (220.61)
Range and dryer loads at 70% — e.g., 8,000 VA range → 5,600 VA and 5,500 VA dryer → 3,850 VA; Exception for 3-wire, 2-phase or 5-wire, 2-phase systems: maximum net calculated load between neutral and any one ungrounded conductor × 140%