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Texas - Journeyman 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
26
Passing score
70
Exam time
110 min
Administered by
PSI Services Contractor
Format
Reference materials allowed

Texas State Portion 26 questions

Cálculos y Teoría 2 Q · 8%
Servicios Eléctricos, Equipos de Servicio y Sistemas Derivados Separadamente 4 Q · 17%
Alimentadores Eléctricos 3 Q · 12%
Cálculos de Circuitos Ramales y Conductores 4 Q · 17%
Métodos de Cableado Eléctrico y Materiales Eléctricos 2 Q · 8%
Equipos y Dispositivos Eléctricos 2 Q · 8%
Motores y Generadores 2 Q · 8%
Dispositivos de Control Eléctrico y Medios de Desconexión 1 Q · 4%
Ocupaciones, Equipos y Condiciones Especiales 3 Q · 12%
Tecnologías de Energía Renovable 1 Q · 4%

Key Distinctions

Continuous Load (Branch Circuit)vsNon-Continuous Load (Branch Circuit)

Continuous loads require conductor ampacity of at least 125% of the load current, while non-continuous loads are calculated at 100%.

NEC 215.2(A)(1)(a)
Feeder Ampacity (Motor Only)vsFeeder Ampacity (Motor + Other Loads)

Motor-only feeders use 125% of largest motor FLC + 100% of all other motor FLCs, while mixed feeders also add 125% of any continuous non-motor loads.

NEC Table 430.250, Section 430.24
Branch Circuit Conductor Sizing (Motor, NEC 430.22)vsFeeder Conductor Sizing (Motors, NEC 430.24)

A single-motor branch circuit conductor must be ≥125% of that motor's FLC, while a motor feeder must be ≥125% of the largest motor FLC plus 100% of all remaining motor FLCs.

NEC Table 430.248, Section 430.22
Temperature Correction FactorvsConduit Fill Adjustment Factor

Temperature correction compensates for ambient heat above the conductor's rated temperature, while conduit fill adjustment derates for heat buildup from multiple current-carrying conductors in the same raceway; both factors are multiplied together against base ampacity.

NEC Table 310.16, Table 310.15(B)(2)(a), Table 310.15(B)(3)(a)
Straight Pull Box (NEC 314.28(A)(1))vsAngle Pull Box (NEC 314.28(A)(2))

Straight pull box minimum length = 8× the largest conduit trade size; angle pull box minimum distance = 6× the largest conduit trade size plus the sum of all other conduit trade sizes on the same wall.

NEC 314.28(A)(1)
Single-Phase Voltage Drop FormulavsThree-Phase Current Formula

Single-phase VD uses a factor of 2 in the numerator (VD = 2×K×I×D / CM), while three-phase current uses √3 (1.732) as the divisor (I = VA / (E × 1.732)).

NEC Chapter 9, Table 8
Motor Overload Protection (NEC 430.32(A)(1)) — Service Factor ≥1.15vsMotor Branch-Circuit OCPD (NEC 430.52, Inverse-Time CB)

Overload protection is set at 125% of the motor nameplate current (for SF ≥1.15), while branch-circuit short-circuit/ground-fault protection via inverse-time CB is set at 250% of the Table FLC (next standard size up if needed).

NEC Section 430.32(A)(1)
Motor Disconnect Rating (NEC 430.110(A))vsMotor Branch Circuit Conductor Ampacity (NEC 430.22)

The disconnect must be rated at least 115% of motor FLC, while branch circuit conductors must have an ampacity of at least 125% of motor FLC.

NEC Table 430.250, Section 430.110(A)
Time-Delay (Dual-Element) Fuse for Motor Protection (NEC Table 430.52)vsInverse-Time Circuit Breaker for Motor Protection (NEC Table 430.52)

Time-delay dual-element fuses are sized at 175% of motor FLC (next standard size up if needed), while inverse-time circuit breakers are sized at 250% of motor FLC (next standard size up if needed).

NEC Table 430.250, Table 430.52, Section 240.6(A)
Sign Load Branch Circuit — Dedicated (NEC 600.5(A))vsSign Load Conductor Sizing — Continuous (NEC 600.5(C))

NEC 600.5(A) prohibits other loads on a sign branch circuit (dedicated use only), while NEC 600.5(C) classifies sign loads as continuous, requiring conductor ampacity ≥125% of the sign load.

NEC 600.5(A), 600.5(C)
3-Phase Transformer Secondary Currentvs3-Phase System Load Current

Both use I = VA / (E × √3), but transformer secondary current is calculated from kVA rating to size protective equipment, while system load current is calculated from total calculated VA to size feeder conductors.

NEC Article 700.4, transformer secondary current formula

Key Terms

Feeder Conductor Minimum Ampacity — Continuous + Non-Continuous Loads NEC 215.2(A)(1)(a)
Per NEC 215.2(A)(1)(a), feeder conductors must have ampacity not less than the non-continuous load plus 125% of the continuous load.
Motor Branch Circuit Conductor Sizing NEC Table 430.250, Section 430.22
Per NEC 430.22, branch circuit conductors supplying a single motor must have an ampacity of not less than 125% of the motor's full-load current from NEC Table 430.248 or 430.250.
Motor Feeder Conductor Sizing NEC Table 430.250, Section 430.24
Per NEC 430.24, feeder conductors supplying multiple motors must have an ampacity of not less than 125% of the largest motor FLC plus 100% of all other motor FLCs.
Overload Protection — Motor with Service Factor ≥1.15 NEC Section 430.32(A)(1)
Per NEC 430.32(A)(1), a motor with a service factor of 1.15 or greater shall have overload protection not exceeding 125% of the motor's nameplate full-load ampere rating.
Motor Disconnect Minimum Rating NEC Table 430.250, Section 430.110(A)
Per NEC 430.110(A), the motor disconnect must be rated at not less than 115% of the motor's full-load current from the applicable NEC table.
Straight Pull Box Minimum Length NEC 314.28(A)(1)
Per NEC 314.28(A)(1), the minimum length of a straight pull box is 8 times the trade size diameter of the largest conduit entering the box.
Angle Pull Box Minimum Distance NEC 314.28(A)(2)
Per NEC 314.28(A)(2), the minimum distance for an angle pull is 6 times the largest conduit trade size on that wall plus the sum of all other conduit trade sizes on the same wall.
Emergency System Battery Minimum Voltage NEC 700.12(C)(4)
Per NEC 700.12(C)(4), storage batteries supplying emergency illumination must maintain voltage at no less than 87½% of nominal voltage for 1½ hours.
Emergency System Ground-Fault Signal Device Maximum Setting NEC 700.6(D)
Per NEC 700.6(D), on solidly grounded wye systems over 150V to ground with protective devices rated 1000A or more, the ground-fault signal device shall be set for a maximum of 1200 amperes.
Sign Branch Circuit — Dedicated Use NEC 600.5(A), 600.5(C)
Per NEC 600.5(A), the branch circuit supplying an electric sign shall supply no other load — it must be a dedicated circuit.
Sign Load — Continuous Load Treatment NEC 600.5(C), 210.19(A)(1), Table 310.16
Per NEC 600.5(C), electric sign loads are considered continuous loads, requiring branch circuit conductor ampacity of not less than 125% of the sign's rated current.
Neon Sign Switch Rating — Non-Inductive NEC 600.6(B)
Per NEC 600.6(B), a control switch not rated for inductive loads must have a current rating not less than twice the total current rating of the transformers it controls.
Conduit Fill — 40% Rule (Multiple Conductors) NEC Chapter 9, Table 4; Chapter 9, Table 5
Per NEC Chapter 9, Table 4, when three or more conductors are installed in a conduit, the total conductor cross-sectional area must not exceed 40% of the conduit's internal cross-sectional area.
Conductor Ampacity Adjustment — Conduit Fill (4–6 CCC) NEC Table 310.16, Table 310.15(B)(2)(a), Table 310.15(B)(3)(a)
Per NEC Table 310.15(B)(3)(a), when 4–6 current-carrying conductors are in a raceway, each conductor's base ampacity must be multiplied by an adjustment factor of 0.80.
Conductor Ampacity Adjustment — Conduit Fill (7–9 CCC) NEC Table 310.16, Table 310.15(B)(2)(a), Table 310.15(B)(3)(a)
Per NEC Table 310.15(B)(3)(a), when 7–9 current-carrying conductors are in a raceway, each conductor's base ampacity must be multiplied by an adjustment factor of 0.70.
Maximum Continuous Load on a Branch Circuit NEC 210.20(A), 210.19(A)(1)
Per NEC 210.20(A), the continuous load on a branch circuit must not exceed 80% of the OCPD rating (equivalently, OCPD rating ÷ 1.25 = maximum continuous load).

Formulas to Know

Continuous Load — Minimum Conductor/OCPD AmpacityMin Ampacity = (Continuous Load × 1.25) + (Non-Continuous Load × 1.00)
Maximum Continuous Load on a CircuitMax Continuous Load = OCPD Rating ÷ 1.25
Motor Branch Circuit Conductor Ampacity (Single Motor)Min Ampacity = Motor FLC (from Table) × 1.25
Motor Feeder Conductor Ampacity (Multiple Motors)Min Ampacity = (Largest Motor FLC × 1.25) + (Sum of All Other Motor FLCs × 1.00)
Adjusted Conductor Ampacity (Temp + Fill Derating)Adjusted Ampacity = Base Ampacity (Table 310.16) × Temperature Correction Factor × Conduit Fill Adjustment Factor
Single-Phase Voltage DropVD = (2 × K × I × D) ÷ CM [K = 12.9 copper; I = amps; D = one-way distance (ft); CM = circular mils]
Three-Phase System CurrentI = VA ÷ (E × √3) [√3 ≈ 1.732]
Three-Phase Transformer Secondary CurrentI = (kVA × 1000) ÷ (E_secondary × 1.732)
Motor Branch-Circuit OCPD — Inverse-Time CB (Max Size)Max CB = Motor FLC × 2.50; if result is not a standard size, round UP to next standard size per NEC 240.6(A)
Motor Branch-Circuit OCPD — Time-Delay (Dual-Element) Fuse (Max Size)Max Fuse = Motor FLC × 1.75; if result is not a standard size, round UP to next standard size per NEC 240.6(A)
Conduit Fill — Minimum Trade Size (Multiple Conductors)Total Fill Area = Σ(Number of each conductor × individual conductor area from Table 5); select smallest conduit from Table 4 where 40% fill area ≥ Total Fill Area
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