NEC ELECTRIC TEST

Question 1

The voltage waveform will lag behind the current waveform in a circuit supplying electricity to capacitive loads:

Accepted Answer

True

Answer

In Capacitor Circuit Voltage waveform lags current waveform and has leading power factor. Inductive circuit will be exactly opposite

Question 2

Which of the following machines is the most efficient?

Accepted Answer

Electrical Transformer

Answer

Electrical Transformer will have higher efficiency as there is no rotating parts and airgap in the flux path involved in it. Generally efficiency of the Transformer is of the order of 95% to 99% during
 full load operation

Question 3

During no-load operation, an induction motor's power factor will be in the range:

Accepted Answer

0.2

Answer

Induction motor during no load condition will draw high magnetizing current. This magnetizing current will not do any useful work (rotating the load). Therefore power factor will be low during no load in Induction Motor

Question 4

Conductors with  _____ marked on the insulation are not allowed to be used in wet locations.

Accepted Answer

THHN

Answer

As shown in Table 310.104(A), conductors with THHN insulation are approved for use in dry and damp locations only and conductors with THWN, THHW, and THW insulation are recognized for use in dry and wet locations.

Question 5

Given: The local utility company provides a 120/240 volt, single-phase electrical system to a one-family dwelling unit with a demand load of
 200 amperes. What is the MINIMUM size of aluminum THW conductors required for this residence's service-entrance conductors?

Accepted Answer

4/0 AWG

Answer

Section 310.15(B)(7)(1) permits one-family dwelling 120/240 volt, single-phase, service-entrance conductors to be sized at an ampacity of not less than 83% of the service rating. 

Therefore, 200 amperes x 83% = 166 amperes

Table 310.15(B)(16) indicates size 4/0 AWG THW aluminum conductors with an allowable ampacity of 180 amperes should be selected for this dwelling.

NEC Practice Test

NEC Practice Test

NEC ELECTRIC TEST