FREE E2 Motors and Transformers Questions and Answers

Question 1

An inspector is examining a 10 HP, 460-volt, 3-phase squirrel-cage motor.
According to NEC Table 430.250, its Full Load Current (FLC) is 14A.
What is the maximum permitted rating for an inverse-time circuit breaker used for branch-circuit short-circuit and ground-fault protection?

Accepted Answer

35A

Answer

25A

Answer

40A

Answer

30A

Question 2

A dry-type transformer is installed indoors in a commercial building. According to NEC Article 450, which of the following is a general requirement for its installation?

Accepted Answer

A disconnecting means must be located in sight of the transformer, unless it is lockable and its location is field-marked on the transformer.

Answer

The transformer must always be installed in a fire-resistant vault.

Answer

The primary overcurrent protection must not exceed 100% of the transformer's rated primary current.

Answer

Ventilating openings can be blocked as long as the ambient temperature does not exceed 30°C.

Question 3

When sizing separate overload protection for a continuous-duty motor with a service factor of 1.15, what is the maximum percentage of the motor's nameplate full-load ampere (FLA) rating that should be used?

Accepted Answer

125%

Answer

115%

Answer

250%

Answer

100%

Question 4

An inspector observes a dry-type transformer with a horizontal top surface installed in a readily accessible electrical room. What specific marking is required on the transformer's top surface according to NEC 450.9?

Accepted Answer

A marking to prohibit storage.

Answer

The transformer's kVA rating and voltage.

Answer

A warning to maintain 3 feet of clearance.

Answer

The date of installation.

Question 5

A motor controller for a 480V motor is located in an electrical room, and the motor itself is located 100 feet away on the factory floor, out of sight from the controller. Which of the following is required by NEC 430.102(B)?

Accepted Answer

A disconnecting means must be installed in sight from the motor and driven machinery location.

Answer

The motor circuit conductors must be oversized by 25%.

Answer

The motor controller must have a horsepower rating.

Answer

A second set of overload heaters must be installed at the motor.

Question 6

For a transformer rated 1000 volts or less with a primary current of 15 amperes, what is the maximum rating of an overcurrent protective device (OCPD) on the primary side if it is the *only* protection for the transformer?

Accepted Answer

125% of the primary current

Answer

250% of the primary current

Answer

150% of the primary current

Answer

115% of the primary current

An inspector is examining a 10 HP, 460-volt, 3-phase squirrel-cage motor.According to NEC Table 430.250, its Full Load Current (FLC) is 14A.What is the maximum permitted rating for an inverse-time circuit breaker used for branch-circuit short-circuit and ground-fault protection?

An inspector is examining a 10 HP, 460-volt, 3-phase squirrel-cage motor.
According to NEC Table 430.250, its Full Load Current (FLC) is 14A.
What is the maximum permitted rating for an inverse-time circuit breaker used for branch-circuit short-circuit and ground-fault protection?