Exam Cheat Sheet · Quick Reference
Texas Master Electrician Calculations Portion
Texas · 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
33
Passing score
70%
Exam time
170 min
Administered by
PSI Services Contractor
Format
Reference materials allowed
Texas State Portion 33 questions
Calculations and Theory
2 Q · 7%
Branch-circuit load calculations for dwelling and non-dwelling occupanciesFeeder and service load calculations including demand factorsMotor circuit conductor sizing and overcurrent protectionConductor ampacity tables and correction/adjustment factorsOptional load calculation methods for dwelling units and multifamily buildingsCooking appliance and clothes dryer demand factor calculationsNeutral load calculations and permitted reductionsOvercurrent protection ratings and tap conductor rules
Electrical Services, Service Equipment, and Separately Derived Systems
8 Q · 27%
Service conductor ampacity sizing and minimum size requirements (Articles 230.23, 230.31, 230.42, 220)Service disconnecting means rating, number, and location requirements (Article 230.70–230.85)Grounding electrode system selection, installation, and sizing for services (Articles 250.50–250.68)Main bonding jumper and system bonding jumper sizing for services and separately derived systems (Articles 250.28, 250.24, 250.30)Separately derived system grounding and bonding requirements including grounding electrode conductor sizing (Article 250.30)Ground-fault protection of equipment requirements for solidly grounded wye services (Article 230.95)Service load calculations including demand factors for dwelling and non-dwelling occupancies (Article 220)Overcurrent protection requirements for service conductors and transformer secondary conductors (Articles 230.90, 450.3)
Electrical Feeders
3 Q · 10%
Minimum feeder conductor ampacity for continuous and noncontinuous loads (125% rule)Feeder overcurrent protection rating requirements (Article 215.3)Feeder and service load calculations using demand factors (Article 220 Parts III and IV)Optional feeder load calculation methods for dwelling units and multifamily buildingsFeeder neutral load calculation and permitted reductions (220.61)Ground-fault protection of equipment for feeders rated 1000 amperes or more (215.10)Feeder tap conductor rules (10-ft, 25-ft, and outside tap provisions per 240.21(B))Surge-protective device requirements for feeders supplying dwelling and similar occupancies (215.18)
Branch Circuit Calculations and Conductors
4 Q · 13%
Minimum conductor ampacity for continuous and noncontinuous branch-circuit loads (125% rule)Branch-circuit ratings, overcurrent protection sizing, and standard ampere ratingsConductor ampacity tables, temperature correction factors, and adjustment factors for bundled conductorsDwelling unit load calculations including general lighting, small-appliance, laundry, and cooking appliance loadsDemand factors for household ranges, dryers, and non-dwelling receptacle and lighting loadsGFCI and AFCI protection requirements by location and occupancy typeMotor branch-circuit conductor sizing and short-circuit/ground-fault protection ratingsMinimum conductor sizes and receptacle ratings for specific branch-circuit sizes (10A through 50A)
Electrical Wiring Methods and Electrical Materials
2 Q · 7%
Conductor ampacity calculations using Tables 310.16 and 310.17 (raceway, free air, and direct burial)Ambient temperature correction factors for conductor ampacity (Table 310.15(B)(1)(1) and (1)(2))Adjustment factors for more than three current-carrying conductors in a raceway or cable (Table 310.15(C)(1))Conduit fill calculations using Chapter 9 Tables for EMT, RMC, IMC, PVC, FMC, and other racewaysConductor sizing for single-phase dwelling services and feeders (Table 310.12(A))Minimum cover requirements for underground installations by wiring method and location (Table 300.5(A))Securing and supporting intervals for specific wiring methods (EMT, RMC, IMC, FMC, LFMC, NM cable, MC cable, PVC)Cable tray fill calculations and ampacity for multiconductor and single-conductor cables (Article 392)
Electrical Equipment and Devices
2 Q · 7%
Motor branch-circuit conductor sizing (125% rule, single and multiple motors)Motor branch-circuit short-circuit and ground-fault protective device ratings (Table 430.52)Motor overload protection ratings and selection (430.32, service factor and temperature rise thresholds)Transformer overcurrent protection ratings (Tables 450.3(A) and 450.3(B))Disconnecting means ratings and current requirements for motors and motor controllersAC/DC motor full-load current table values (Tables 430.247–430.250) used for calculationsPanelboard and switchboard overcurrent protection and short-circuit current ratingsAir-conditioning and refrigerating equipment branch-circuit conductor and protective device sizing (Article 440)
Motors and Generators
6 Q · 20%
Branch-circuit conductor sizing for single and multiple motors (430.22, 430.24)Motor branch-circuit short-circuit and ground-fault protective device ratings using Table 430.52(C)(1)Motor overload protection sizing percentages for continuous-duty motors (430.32)Full-load current determination from Tables 430.247–430.250 for AC and DC motorsMotor feeder conductor ampacity and feeder overcurrent protection rating (430.24, 430.62)Disconnecting means rating requirements at 115% of motor full-load current (430.110)Generator conductor ampacity at 115% of nameplate rating and overcurrent protection (445.12, 445.13)Hermetic refrigerant motor-compressor branch-circuit conductor sizing and short-circuit protection (440.22, 440.32)
Electrical Control Devices and Disconnecting Means
1 Q · 3%
Motor disconnecting means type, rating, and location requirements (Article 430 Part IX)Motor branch-circuit short-circuit and ground-fault protective device rating calculations using Table 430.52(C)(1)Motor controller ratings, markings, and horsepower requirements (Article 430 Part VII)Motor overload protection sizing percentages and device selection (Article 430 Part III)Disconnecting means current rating calculations including 115% requirement and combination loadsAC/DC disconnecting means requirements for hermetic refrigerant motor-compressors (Article 440 Part II)Service disconnecting means rating, location, and number of disconnects (Article 230 Part VI)Switch ratings and uses including general-use snap switches and motor-circuit switches (Article 404)
Special Occupancies, Equipment, and Conditions
1 Q · 3%
Hazardous location classification (Class I, II, III; Division 1 and 2; material groups A-G)Protection techniques for hazardous locations (explosionproof, dust-ignitionproof, intrinsic safety, purged/pressurized, etc.)Conductor ampacity calculations for electric welders (arc and resistance; duty cycle factors; group welder calculations)Overcurrent protection sizing for electric welders (arc welders at 200% and resistance welders at 300%)EVSE branch circuit, overcurrent protection, and load calculations (125% continuous load factor; energy management systems)Wiring methods and sealing requirements in hazardous classified locations (Class I conduit seals; Class II sealing; Articles 501-503)Health care facility essential electrical system branch sizing and load calculations (Articles 517; feeder demand factors; branch circuit requirements)Crane and hoist conductor ampacity and overcurrent protection calculations (Table 610.14; duty cycle; multiple motor demand factors)
Renewable Energy Technologies
1 Q · 3%
PV system maximum DC voltage calculations using temperature correction factors (Table 690.7(A))PV circuit maximum current calculations and conductor ampacity sizing (690.8)Overcurrent protection device ratings for PV and renewable energy circuits (690.9, 694.15, 706.31)Busbar and feeder sizing for interconnected power source load-side connections (705.12)Wind electric system circuit sizing and overcurrent device ratings (694.12)Energy storage system circuit sizing and overcurrent protection calculations (706.30, 706.31)Conductor ampacity for interconnected power production source output circuits (705.28)
Key Distinctions
Single-phase current formulavsThree-phase current formula
Single-phase uses I = VA / E (e.g., 45,000/240 = 187.5A), while three-phase divides by line voltage times √3, I = VA / (E × 1.732) (e.g., 75,000/(208×1.732) = 208.2A).
Three-phase current formula: I = kVA × 1,000 / (E × 1.732)Single-phase voltage-drop formulavsThree-phase voltage-drop formula
Single-phase uses the factor 2 — VD = (2 × K × I × D)/CM — while three-phase substitutes 1.732 for the 2, VD = (1.732 × K × I × D)/CM.
NEC 2026 Chapter 9, Table 8Motor nameplate FLAvsTable 430.250 FLC
Overload protection is sized from the motor's actual nameplate current (e.g., 28A × 1.25 = 35.0A), while branch-circuit conductors and feeders are sized from the Table 430.250 full-load current per 430.6(A)(1) (e.g., 65A × 1.25 = 81.25A).
NEC 2026 Section 430.32Continuous loadvsNon-continuous load
Continuous load is multiplied by 125% before sizing conductors/OCPD, while non-continuous load is counted at 100% (e.g., 85A cont. × 1.25 + 40A non-cont. = 146.25A).
NEC 2026 Section 230.42Grounding electrode conductor (Table 250.66)vsEquipment grounding conductor (Table 250.122)
The GEC is sized from the size of the largest ungrounded service-entrance conductor (4/0 Cu → 2 AWG Cu GEC), while the EGC is sized from the rating of the overcurrent device (400A OCPD → 3 AWG Cu EGC).
NEC 2026 Table 250.66THHN (90°C column)vsTHWN (75°C column)
THHN ampacity calculations start from the 90°C column of Table 310.16 (and use the 90°C temperature-correction column), while THWN is rated 75°C and starts from the 75°C column (e.g., 4/0 Cu: 260A/90°C basis for THHN vs 230A for THWN).
NEC 2026 Table 310.16, Table 310.15(B)(1)(1), Table 310.15(C)(1)Branch-circuit conductor sizing, 210.19(A)(1)vsFeeder conductor sizing, 215.2(A)(1)(a)
Both apply 125% to continuous load, but 210.19(A)(1) governs branch-circuit conductors (48A × 1.25 = 60A) and 215.2(A)(1)(a) governs feeders as non-continuous load plus 125% of continuous load.
NEC 2026 Section 210.19Straight pull box sizingvsAngle pull box sizing
Per 314.28(A)(1) a straight pull requires a minimum length of 8 × the trade diameter of the largest raceway (3" → 24 in.), whereas the 6 × largest-conduit figure belongs to the angle-pull formula.
NEC 2026 Section 314.28Largest motor in a feeder calculationvsAll other motors in a feeder calculation
Per 430.24 the largest motor's FLC is taken at 125% while every other motor's FLC is added at 100% (65A × 1.25 + 34A + 14A = 129.25A).
NEC 2026 Table 430.250, Section 430.24Chapter 9, Table 5vsChapter 9, Table 4
Table 5 gives the cross-sectional area of each insulated conductor (10 AWG THHN = 0.0211 sq in.), while Table 4 gives the allowable raceway fill area for the trade size (1" EMT at 40% = 0.346 sq in.).
NEC 2026 Chapter 9, Table 5Chapter 9, Table 8vsTable 310.16
Table 8 supplies circular-mil (CM) areas used in voltage-drop math (4 AWG Cu = 41,740 CM), while Table 310.16 supplies allowable ampacities used for conductor sizing (3/0 Cu at 75°C = 200A).
NEC 2026 Chapter 9, Table 8EMT run with no pull pointvsEMT run with a conduit body added mid-run
358.26 limits bends to 360° between pull points, so adding a conduit body (a pull point) mid-run permits each section on either side of it to have up to 360° of bends.
NEC 2026 Section 358.24(B) (EMT — number of bends in one run)Key Terms
Full-load current (FLC), Table 430.250 NEC 2026 Table 430.250, Section 430.22, Section 430.6
The tabulated three-phase motor current used for conductor and feeder sizing per 430.6(A)(1) (e.g., 50 HP @ 460V = 65A; 25 HP = 34A; 10 HP = 14A; 40 HP = 52A; 30 HP @ 208V = 88A).
Motor overload protection, 430.32(A)(1) NEC 2026 Section 430.32
For a motor with a service factor of 1.15 or greater, the maximum overload trip setting is 125% of the motor's nameplate full-load amperes, not the table FLC.
Continuous load NEC 2026 Section 210.19, 210.20, 210.11
A load whose conductors and overcurrent device must be rated at not less than 125% of that load per 210.19(A)(1), 210.20(A), 215.2(A)(1)(a) and 230.42(A)(1).
Service-entrance conductor minimum ampacity, 230.42(A)(1) NEC 2026 Section 230.42
Service-entrance conductors must have an ampacity not less than the non-continuous load plus 125% of the continuous load.
Grounding electrode conductor (GEC), Table 250.66 NEC 2026 Table 250.66
The conductor sized from the size of the largest ungrounded service-entrance conductor; insulation type does not affect the sizing (4/0 Cu or 500 kcmil Al → 2 AWG Cu; 3/0 Cu → 4 AWG Cu; 400 kcmil Cu → 1/0 Cu).
Equipment grounding conductor (EGC), Table 250.122 NEC 2026 Table 250.122
The conductor sized from the rating of the overcurrent protective device ahead of the circuit (300A → 4 AWG Cu; 400A → 3 AWG; 500A → 2 AWG; 600A → 1 AWG).
Ambient temperature correction factor, Table 310.15(B)(2)(a) NEC 2026 Table 310.16, Table 310.15, Table 310.15
A multiplier applied to base ampacity for ambients above 30°C, selected by insulation temperature column (90°C: 0.91 at 36–40°C, 0.87 at 41–45°C; 75°C: 0.88 at 36–40°C).
Adjustment factor for current-carrying conductors (CCC), Table 310.15(B)(3)(a) NEC 2026 Table 310.16, Table 310.15, Table 310.15
A multiplier applied when more than three current-carrying conductors share a raceway (6 CCC = 0.80; 9 CCC = 0.70).
40% conduit fill NEC 2026 Chapter 9, Table 5
The maximum permitted raceway fill area from Chapter 9, Table 4 when more than two conductors are installed (EMT: 3/4" = 0.213, 1" = 0.346, 1-1/4" = 0.598, 1-1/2" = 0.814, 2" = 1.342 sq in.).
Pull point, NEC 358.26 NEC 2026 Section 358.24(B) (EMT — number of bends in one run)
A box or conduit body that resets the bend count; 358.26 limits an EMT run to 360° of bends between pull points.
Straight pull, NEC 314.28(A)(1) NEC 2026 Section 314.28
A pull box configuration in which the minimum box length must be at least 8 times the trade diameter of the largest raceway entering it.
Separately derived system, NEC 250.30 NEC 2026 Article 450, Section 250.30
A system such as a transformer secondary whose conductors are sized from the transformer's calculated full-load secondary current.
Standard OCPD size, NEC 240.6(A) NEC 2026 Section 230.90, NEC 240.6
The listed standard ampere ratings (…100, 110, 125, 150…) from which the next size at or above the calculated load is selected, per 230.90 the OCPD must be rated not less than the calculated load.
Range demand, Table 220.55 Column C with Note 1 NEC 2026 Table 120.55, Note 1
One range rated 12 kW or less has an 8 kW demand; Note 1 increases the Column C value 5% for each kW (or fraction) over 12 kW.
K factor (voltage drop constant) NEC 2026 Chapter 9, Table 8
The resistivity constant used in voltage-drop calculations, taken as 12.9 for copper (an aluminum K value gives a larger drop).
Parallel conductors, 310.10(G) NEC 2026 Table 310.16, Section 310.10
Two or more conductors per phase, permitted only in sizes 1/0 AWG and larger (310.10(G)(1)) and required to be the same length, material, circular-mil size, insulation type, and termination method (310.10(G)(2)); each set is sized for the total current divided by the number of sets (416.4A ÷ 2 = 208.2A per conductor → 4/0 AWG).
Formulas to Know
Three-phase current / transformer full-load current
I = VA / (E × 1.732), or I = kVA × 1000 / (E × √3); e.g., 75,000/(208 × 1.732) = 208.2ASingle-phase current / transformer full-load current
I = VA / E (use line-to-line voltage); e.g., 45,000/240 = 187.5A; 42,500/240 = 177AVoltage drop, single-phase and three-phase
Single-phase: VD = (2 × K × I × D) / CM; Three-phase: VD = (1.732 × K × I × D) / CM, with K = 12.9 for copper, D = one-way distance, CM from Chapter 9 Table 8Adjusted (derated) conductor ampacity
Adjusted ampacity = Table 310.16 base ampacity (correct insulation column) × temperature correction factor × CCC adjustment factor; e.g., 75 × 0.91 × 0.80 = 54.6AMinimum conductor ampacity with mixed loads (feeder or service)
Minimum ampacity = non-continuous load (100%) + continuous load × 1.25; e.g., 48A × 1.25 + 32A = 92A; (80,000 × 1.25) + 35,000 = 135,000 VAMaximum continuous load a conductor may serve
Max continuous load = conductor ampacity ÷ 1.25; e.g., 200A ÷ 1.25 = 160AMotor feeder minimum ampacity (430.24)
Feeder ampacity = 125% of largest motor FLC + 100% of all other motor FLCs (+ 125% of any continuous non-motor load per 215.2(A)(1)); e.g., 65 × 1.25 + 34 + 14 = 129.25A; 88 × 1.25 + 40 × 1.25 = 160AMotor branch-circuit conductor and overload sizing
Conductors: 125% × Table 430.250 FLC (65 × 1.25 = 81.25A). Overload (SF ≥ 1.15): 125% × nameplate FLA (28 × 1.25 = 35.0A)Minimum number of lighting branch circuits
Circuits = (total VA × 1.25 for continuous) ÷ (circuit volts × circuit amps), always round UP; e.g., 656,250 ÷ (277 × 20) = 118.5 → 119; 45,000 ÷ 2,400 = 18.75 → 19Conduit fill and range demand
Fill: total area = Σ (qty × Table 5 area per conductor), then pick the Table 4 trade size whose 40% column exceeds it; e.g., (12 × 0.0507) + (8 × 0.0211) = 0.7772 → 1-1/2" EMT. Range: demand = 8 kW × [1 + 0.05 × (kW over 12)]; 16 kW → 8 × 1.20 = 9.6 kW