Exam Cheat Sheet · Quick Reference

South Carolina Residential Electrical

South Carolina  ·  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
60
Passing score
73%
Exam time
180 min
Administered by
PSI Services Contractor
Format
Reference materials allowed

South Carolina State Portion 60 questions

General Electrical Knowledge 13 Q · 22%
Calculate voltage, current and resistance in series, parallel and combination circuitsCalculate power used in a circuitUnderstand and apply fundamental ac theoryCalculate voltage drop for branch circuits or feedersTroubleshoot and test systemsUnderstand and apply definitionsInstall smoke alarmsRead and interpret blueprints and drawingsPerform quantity take-offsEnsure structural requirements not compromised
Services, Feeders, and Branch Circuits 15 Q · 25%
Install servicesInstall feedersInstall branch circuitsInstall temporary installationsInstall motors used in dwellingsInstall three-phase service
Overcurrent Protection 5 Q · 8%
Understand and apply knowledge of NEC overcurrent protection requirements
Grounding and Bonding 6 Q · 10%
General requirementsUse tables to obtain the required sizes of grounding electrode conductorUse tables to obtain the required sizes of equipment grounding conductor
Conductors and Cables 5 Q · 8%
Install underground conductors and cablesPerform vertical installationsSelect a conductorArmored Cable Type ACMetal-Clad Cable Type MCNonmetallic-Sheathed Cable Type NM, NMC, NMSService Entrance Cables: Type SE and USEUnderground Feeder and Branch Circuit Cable Type UF
Raceways and Boxes 4 Q · 7%
Understand and apply general raceway requirementsUnderstand and apply general box requirementsInstall RMC (rigid metal conduit)Install EMT (electric metallic conduit)Install IMC (intermediate metal conduit)Install RNC (rigid non-metallic conduit)Install FMC (flexible metal conduit)Install LFMC (liquid-tight flexible metal conduit)Install FMT (flexible metallic tubing)Calculate area of raceway and number of conductors (conduit fill)Install outlet, device, pull and junction boxesCalculate box volume and fill
Lighting 4 Q · 7%
Install fixturesGround fixturesInstall fixture wiringUnderstand fixture construction requirementsInstall fluorescent fixturesInstall recessed fixturesInstall switches
Specialty – pool/spa, garages, generators, wheelchair lifts 4 Q · 7%
Install wiring for pools, spas and hot tubsInstall bonding and grounding for swimming pool, hot tub and spa bonding and all associated equipmentInstall pool, spa and hot-tub lightingInstall generatorsInstall wheelchair liftsInstall equipment in garages
Safety 4 Q · 7%
Understand Responsibility for Providing Personal Protective EquipmentPrepare Emergency Action PlansEnsure Safety Training is Conducted when NeededEnsure First Aid Kit is Available per RequirementsEnsure Personal Protective Equipment is Used CorrectlyUse All Tools and Equipment in Accordance with RequirementsUtilize Ladders in Accordance with RequirementsMaintain Material Safety Data Sheets (MSDS)Provide Fall Protection

Key Distinctions

Main bonding jumpervsSystem bonding jumper

The main bonding jumper is the connection between the grounded circuit conductor and the equipment grounding conductor at the service, while the system bonding jumper makes that same type of connection at a separately derived system such as a transformer.

NEC 2017 Article 100 — Bonding Jumper, Main definition
Grounding electrode conductor (sizing basis)vsEquipment grounding conductor (sizing basis)

The GEC is sized from Table 250.66 based on the size of the largest ungrounded (service) conductor, while the EGC is sized from Table 250.122 based on the rating or setting of the automatic overcurrent device ahead of the equipment.

NEC 2017 Section 250.66 / Table 250.66
Motor overload heater sizingvsMotor branch-circuit conductor and overcurrent device sizing

Per 430.32 overload heaters are sized on the motor nameplate amperes, whereas branch-circuit conductors and overcurrent devices are sized from the full-load current tables.

NEC 2017 Section 430.32
Single-phase formulasvsThree-phase formulas

Three-phase calculations include the 1.73 (√3) multiplier — in the denominator for amperes, as the multiplier for kW/kVA, and in place of the factor 2 in voltage drop — while single-phase formulas do not use 1.73 (the factor 2 is used for two-phase, four-wire).

Ugly's Electrical References 2020, Formulas for Calculating Amperes, Horsepower, Kilowatts, and kVA
AC circuit formulasvsDC circuit formulas

AC formulas include power factor (and 1.73 for three phase), while DC formulas use neither power factor nor the 2 or 1.73 multipliers (e.g., DC amperes I = (kW × 1000) ÷ E; DC HP = (E × I × %EFF) ÷ 746).

Ugly's Electrical References 2020, Formulas for Calculating Amperes, Horsepower, Kilowatts, and kVA
THHN insulationvsTHW insulation

THHN is rated 90°C and is suitable for dry and damp locations only, while THW is rated 75°C and is suitable for dry and wet locations (TW is 60°C, RHW is 75°C dry and wet).

NEC 2017 Section 310.104, Table 310.104(A)
Type USE cablevsType UF cable

Type USE shall not be used for interior wiring (identified for underground use only), while Type UF is permitted underground including direct burial and also for interior wiring when installed per applicable requirements.

NEC 2017 Section 338.12(B)(1)
Voltage (of a circuit)vsVoltage to ground

Voltage of a circuit is the greatest rms difference of potential between any two conductors of the circuit (240 V on a 120/240 V circuit), while voltage to ground is the separately defined measurement from an ungrounded conductor to ground (120 V).

NEC 2017 Article 100 (Definition of Voltage of a Circuit)
Annex C conduit fill tablesvsChapter 9 Table 1 individual-area method

Annex C tables apply only when all conductors are the same size and type (and decimals of 0.8 or larger may be rounded up), while conductors of different sizes or insulation types require summing individual cross-sectional areas and comparing to the allowable fill area.

NEC 2017 Chapter 9, Table 1 and Notes to Tables
240.4(B) next-higher-standard-size permissionvs240.4(C) devices rated over 800 amperes

The next-higher-standard-size rounding permitted by 240.4(B) does not apply above 800 amperes; where the overcurrent device exceeds 800 A the conductor ampacity must equal or exceed the device rating.

NEC 2017 Section 240.4(C)
120/208-volt, 3-phase, 4-wire wye color codevs277/480-volt, 3-phase, 4-wire wye color code

At 120/208 V the conventional colors are A = black, B = red, C = blue with white/gray neutral, while at 277/480 V they are A = brown, B = orange, C = yellow with a gray neutral.

Ugly's Electrical References 2020, Common Electrical Distribution Systems
Minimum cover for rigid metal conduitvsMinimum cover for direct burial cable / rigid nonmetallic conduit

Per Table 300.5, RMC requires only 6 inches of cover in most locations, compared with 24 inches for direct burial cables and 18 inches for rigid nonmetallic conduit without concrete encasement.

NEC 2017 Section 300.5
Peak let-through current (current-limitation chart)vsApparent prospective RMS symmetrical let-through current

Peak let-through current corresponds to the mechanical forces exerted on conductors and equipment during a fault, while the apparent prospective RMS symmetrical let-through value corresponds to the heating effect (clearing time being less than ½ cycle in the current-limiting range).

Ugly's Electrical References 2020, Component Protection (Fuse Let-Through Charts)

Key Terms

Continuous load NEC 2017 Article 100 — Continuous Load definition
A load where the maximum current is expected to continue for 3 hours or more; conductors and devices for such loads are typically rated at 125% of the continuous load current.
Nominal voltage 29 CFR 1926, §1926.449 (Voltage, nominal definition)
A nominal value assigned to a circuit or system for the purpose of conveniently designating its voltage class (as 120/240, 480Y/277, 600, etc.), with actual operating voltage permitted to vary within a range allowing satisfactory equipment operation.
Voltage (of a circuit) NEC 2017 Article 100 (Definition of Voltage of a Circuit)
The greatest root-mean-square (rms) (effective) difference of potential between any two conductors of the circuit concerned.
Main bonding jumper NEC 2017 Article 100 — Bonding Jumper, Main definition
The connection between the grounded circuit conductor and the equipment grounding conductor at the service.
System bonding jumper NEC 2017 Article 100 (Definition: Bonding Jumper, System)
The connection between the grounded circuit conductor and the supply-side bonding jumper, the equipment grounding conductor, or both, at a separately derived system.
Grounding electrode conductor NEC 2017 Article 100 — Grounding Electrode Conductor definition
A conductor used to connect the system grounded conductor or the equipment to a grounding electrode or to a point on the grounding electrode system.
Bonding conductor or jumper NEC 2017 Article 100 (Definition: Bonding Conductor or Jumper)
A reliable conductor used to ensure the required electrical conductivity between metal parts required to be electrically connected, important where boxes have concentric or eccentric knockouts that can impair conductivity.
Tap conductor NEC 2017 Section 240.2
A conductor, other than a service conductor, that has overcurrent protection ahead of its point of supply exceeding the value permitted for similar conductors protected as described in 240.4.
Current-limiting overcurrent protective device NEC 2017 Section 240.2
A device that, when interrupting currents in its current-limiting range, reduces the current flowing in the faulted circuit to a magnitude substantially less than that obtainable in the same circuit if the device were replaced with a solid conductor of comparable impedance.
Multiwire branch circuit NEC 2017 Section 210.4(A)
A branch circuit permitted to be considered as multiple circuits whose conductors must all originate from the same panelboard or similar distribution equipment and be provided with a means to simultaneously disconnect all ungrounded conductors where the circuit originates.
Electrically safe work condition Ugly's Electrical References 2020, Electrical Safety Definitions (from NFPA 70E)
A state in which a conductor or circuit part has been disconnected, locked/tagged out per established standards, tested to verify the absence of voltage, and, if necessary, temporarily grounded for personnel protection.
Effective ground-fault current path NEC 2017 Section 250.4(A)(5)
The intended fault-return path required by 250.4(A)(5); the earth shall not be considered an effective ground-fault current path because its resistance is too high to reliably operate overcurrent devices.
Type NM cable NEC 2017 Section 334.10(1)
Nonmetallic-sheathed cable (with Types NMC and NMS) permitted in one- and two-family dwellings and their attached or detached garages and storage buildings.
Type UF cable NEC 2017 Section 340.10
A factory assembly of insulated conductors with nonmetallic material suitable for direct burial, permitted underground including direct burial and also for interior wiring when installed per applicable requirements.
Objectionable current NEC 2017 Section 250.6(B)
Current resulting from multiple grounding connections; where it occurs, one or more but not all of the grounding connections may be discontinued provided 250.4(A)(5) or (B)(4) requirements are still met.
Horsepower Ugly's Electrical References 2020, Formulas for Calculating Amperes, Horsepower, Kilowatts, and kVA
The energy required to lift 33,000 pounds one foot in one minute; electrically equivalent to 745.6 watts, commonly rounded to 746 watts.

Formulas to Know

Ohm's Law current and power from voltage and resistanceI = E ÷ R (e.g., 120 V ÷ 12 Ω = 10 A); P = E² ÷ R (e.g., 120² ÷ 12 = 1,200 W)
Amperes when kilowatts are knownSingle-phase: I = (kW × 1000) ÷ (E × PF); Three-phase: I = (kW × 1000) ÷ (E × PF × 1.73); DC: I = (kW × 1000) ÷ E
Amperes for a single-phase AC motor when horsepower is knownI = (HP × 746) ÷ (E × %EFF × PF); e.g., (0.5 × 746) ÷ (115 × 0.92 × 0.80) = 4.4 A
Horsepower from volts and amperesSingle-phase AC: HP = (E × I × %EFF × PF) ÷ 746; DC: HP = (E × I × %EFF) ÷ 746 (no PF, no 1.73)
Kilowatts and kilovolt-amperes1φ kW = (E × I × PF) ÷ 1000; 3φ kW = (E × I × PF × 1.73) ÷ 1000; 3φ kVA = (E × I × 1.73) ÷ 1000 (PF is not used for kVA)
Voltage drop and percent voltage dropSingle-phase: Vd = (2 × K × L × I) ÷ Cm; Three-phase: Vd = (1.73 × K × L × I) ÷ Cm, with K = 12.9 for copper and 21.2 for aluminum at 75°C; %Vd = Vd ÷ source voltage × 100 (e.g., 7 V ÷ 240 V = 2.9%); NEC recommends not exceeding 5% total, 3% each
Ampacity correction and adjustment (derating)Corrected ampacity = base ampacity × ambient temperature correction factor × conductor-count adjustment factor; base tables assume 30°C ambient (e.g., 100 A × 0.88 at 40°C/75°C × 0.80 for 4–6 current-carrying conductors = 70.4 A)
Cost of operating an applianceCost = Watts × Hours Used × Rate per kWh ÷ 1000 (e.g., 5000 W × 360 h × $0.15 ÷ 1000 = $270)
Feeder conductor ampacity for multiple motors (430.24)Minimum ampacity = (125% × FLC of largest motor) + sum of FLCs of all other motors (e.g., 1.25 × 65 A + 40 A = 121.25 A)
Short-circuit estimating rulesTransformer %Z = applied primary voltage ÷ rated primary voltage (9.6 ÷ 480 = 2%Z); motor short-circuit contribution ≈ total motor current × 4; at a single-phase center-tapped transformer, I(L-N) = 1.5 × I(L-L)
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