Master Electrician (NEC) Practice Test
Preguntas frecuentes
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Un banco completo de preguntas originales de Master Electrician (NEC) en las áreas oficiales, con el peso del examen real y explicaciones. Gratis, sin registro.
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Unas 150 preguntas, 300 minutos, y necesitas 75% para aprobar. Practica por tema aquí y luego haz el simulacro cronometrado para medir tu preparación.
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Preguntas de práctica de ejemplo
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- 1. Calculations
A single-family dwelling has 2,000 sq ft of habitable floor area. Using the standard calculation method at 3 VA per sq ft, what is the general lighting and general-use receptacle load before any demand factors?
- a.3,000 VA
- b.6,000 VA
- c.4,000 VA
- d.8,000 VA
Respuesta: b
Explicación: General lighting is figured at 3 VA per sq ft: 2,000 sq ft x 3 VA = 6,000 VA. This value is calculated before applying the general-lighting demand factors.
- 2. Services & Distribution
What is the maximum number of service disconnecting means permitted for a single set of service-entrance conductors (each in a separate enclosure)?
- a.Eight
- b.Six
- c.One
- d.Four
Respuesta: b
Explicación: A service is limited to a maximum of six disconnecting means. In the 2023 NEC each of the up-to-six disconnects must be in a separate enclosure or be part of listed equipment.
Fuente: 2023 NEC 230.71
- 3. Advanced Wiring
The equipotential bonding grid around a permanently installed pool must use a solid copper conductor no smaller than:
- a.#4 AWG
- b.#8 AWG
- c.#6 AWG
- d.#10 AWG
Respuesta: b
Explicación: Pool equipotential bonding must use an insulated, covered, or bare solid copper conductor not smaller than #8 AWG.
Fuente: 2023 NEC 680.26(B)
- 4. Theory & Design
A transformer has a 4:1 turns ratio and a 10-A primary current. What is the secondary current (ideal)?
- a.2.5 A
- b.40 A
- c.10 A
- d.20 A
Respuesta: b
Explicación: Current is inversely proportional to the turns ratio: Is = Ip x (Np/Ns) = 10 x 4 = 40 A.
- 5. Calculations
A 75-kVA transformer with a 208-A secondary (over 9 A) is protected on both the primary and the secondary. What is the maximum secondary overcurrent device (next higher standard permitted)?
- a.300 A
- b.260 A
- c.250 A
- d.225 A
Respuesta: a
Explicación: Table 450.3(B) allows up to 125% on the secondary where both sides are protected: 208 x 1.25 = 260 A. Since 260 A is not a standard size, Note 1 permits the next higher standard rating, 300 A. Trap: 250 A is the next lower standard and would be too small to carry full secondary load.
Fuente: 2023 NEC 450.3(B)
- 6. Calculations
A one-family dwelling has 2,500 sq ft of habitable floor area. Using the standard method at 3 VA per sq ft, what is the general lighting and general-use receptacle load before demand factors?
- a.9,000 VA
- b.5,000 VA
- c.6,000 VA
- d.7,500 VA
Respuesta: d
Explicación: 2023 NEC 220.41 figures dwelling general lighting at 3 VA/sq ft: 2,500 x 3 = 7,500 VA, calculated before the 220.42 demand factors are applied.
- 7. Calculations
A box contains five #12 AWG and three #10 AWG conductors and nothing else. Using the box-fill volume allowances, what minimum box volume is required?
- a.16.5 cu in
- b.20.0 cu in
- c.17.25 cu in
- d.18.75 cu in
Respuesta: d
Explicación: 2023 NEC Table 314.16(B): #12 = 2.25, #10 = 2.5 cu in. (5 x 2.25) + (3 x 2.5) = 11.25 + 7.5 = 18.75 cu in.
- 8. Services & Distribution
Where two ground rods are used as the grounding electrode, what is the minimum required spacing between them?
- a.8 ft
- b.3 ft
- c.10 ft
- d.6 ft
Respuesta: d
Explicación: 2023 NEC 250.53(A)(3): rod, pipe, or plate electrodes that supplement each other must be at least 6 ft apart.
- 9. Advanced Wiring
A hospital's essential electrical system for a Type 1 facility is divided into which branches?
- a.isolated and grounded branches
- b.life safety, critical, and equipment branches
- c.emergency and legally required branches
- d.normal and standby branches only
Respuesta: b
Explicación: 2023 NEC 517.30: the Type 1 essential electrical system consists of the life safety branch, the critical branch, and the equipment branch.
- 10. Theory & Design
A transformer has a 10:1 turns ratio and a 5-A primary current. What is the ideal secondary current?
- a.5 A
- b.50 A
- c.15 A
- d.0.5 A
Respuesta: b
Explicación: Current is inversely proportional to the turns ratio: Is = Ip x (Np/Ns) = 5 x 10 = 50 A.