Motors & EquipmentPregunta 89 de 120
A 30-horsepower, 460-volt three-phase motor has a table full-load current of 40 amperes. What is the minimum ampere rating of the disconnecting means?
a.50 amperes
b.40 amperes
c.46 amperes
d.60 amperes
Explicación
The disconnecting means must have an ampere rating of at least 115 percent of the full-load current: 40 x 1.15 = 46 A, so a 60-ampere switch would be the practical selection. The 40-ampere answer omits the 115 percent factor entirely, and 50 or 60 amperes are available equipment ratings rather than the calculated minimum the question asks for.
Referencia Legal: 2023 NEC §430.110(A)Practica las 120 preguntas gratis — sin registro.
Preguntas relacionadas de este tema
- For that 34-ampere three-phase squirrel-cage motor, what is the maximum inverse-time circuit breaker permitted for branch-circuit short-circuit and ground-fault protection, using the next standard size allowance?
- For the same 34-ampere motor, what is the maximum dual-element time-delay fuse permitted at the standard percentage?
- A 5-horsepower, 230-volt single-phase motor has a table full-load current of 28 amperes. What is the minimum copper branch-circuit conductor at 75 degrees C terminations?
- A feeder supplies a 25-horsepower motor (34 amperes) and a 10-horsepower motor (14 amperes), both 460 volts three phase. What minimum conductor ampacity is required?
- For that same two-motor feeder, if the largest branch-circuit protective device is 90 amperes, what is the maximum feeder overcurrent device rating?
- When sizing motor branch-circuit conductors and short-circuit protection, which current value must be used?
Última revisión: · proceso editorial
Equipo Editorial de PrepPass · Verificado con Journeyman Electrician Licensing Exam (NEC-based) · Cómo revisamos