Unit 7: AC Motor Calculations

Question 1

Fill in the blank:

For household electric ranges of 83⁄4 kW or more rating, the minimum branchcircuit rating shall be _____.

Answer 1

40 amperes

Question 2

Fill in the blank:

Disregarding exceptions, luminaires installed under metal-corrugated sheet roofing decking shall be installed and supported so there is not less than _____ clearance from the roof decking to the top of the luminaires.

Answer 2

11⁄2 inches

Question 3

For the purpose of calculating the general lighting load for a dwelling unit, the floor area should include all the following except:

a. kitchens
b. bathrooms
c. an unfinished basement intended for future living space
d. an open porch not adaptable for future use

Answer 3

d. an open porch not adaptable for future use

Question 4

Fill in the blank:

Where flexible cord is approved for use and used with a specific listed appliance, it shall be considered to be protected _____.

Answer 4

when applied within the appliance listing requirements

Question 5

Fill in the blank:

Electrical equipment, such as distribution panelboards, motor controllers, and motor control centers that are located in other than dwelling units, and are likely to require examination, adjustment, servicing, or maintenance while energized shall be field or factory marked to warn qualified persons of _____.

Answer 5

potential electric arc flash hazards

Question 6

Determine the required ampacity of the branch-circuit conductors to supply a continuous-duty, Design B, 3-phase, 208-volt, 10 hp, ac motor.

Answer 6

38.5 amperes

Question 7

What is the maximum ampere rating permitted for a 125-volt, single-phase, receptacle having a cord-and-plug connected motor-load that does not have overload protection?

Answer 7

15 amperes

Question 8

True or False:

Panelboards and/or loadcenters housing inverse-time circuit breakers shall not be located in clothes closets, in bathrooms and over steps of a stairway.

Answer 8

TRUE

Question 9

Fill in the blank:

Fastened in place utilization equipment, other than luminaires, that is connected to a branch circuit with other loads shall not exceed _____ of the branch circuit rating.

Answer 9

50 percent

Question 10

Fill in the blank:

In compliance with the NEC, a 3 in. x 2 in. x 11⁄2 in. metal device box may contain no more than _____ size 12 AWG conductors.

Answer 10

three

Question 11

Fill in the blank:

The workspace in front of electrical equipment such as panelboards, switchboards and motor control centers rated 1000 volts or less, shall be at least _____ wide or the width of the equipment, whichever is greater.

Answer 11

18 inches

Question 12

Fill in the blank:

Each receptacle of dc plugging boxes in motion picture studios shall be rated at not less than _____.

Answer 12

30 amperes

Question 13

Where a retail clothing store has an actual connected fluorescent general lighting load of 14,000 VA how many 120-volt, 20-ampere, single-phase branchcircuits are required for the general lighting? Given: The lighting loads will be used continuously throughout the business day.

Answer 13

eight

14,000 VA (continuous load) x 125%= 17,500 VA
120 volts x 20 amperes = 2,400 VA (one circuit)
17,500 VA (load) = 7.29 = 8 – 120 volt, 20-ampere lighting circuits
2,400 VA (circuit)

Question 14

Fill in the blank:

The NEC mandates specific branch-circuits, receptacle outlets and utilization equipment to be provided with a ground-fault circuit interrupter (GFCI); this device is intended _____.

Answer 14

for the protection of personnel

Question 15

Fill in the blank:

For a grounded electrical system, the equipment grounding conductor shall be sized in accordance with the _____.

Answer 15

overcurrent protective device

Question 16

Fill in the blank:

When a device box is installed in a wall having a gypsum (drywall) surface, those surfaces that are broken or incomplete around the device box employing a flush-type faceplate shall be repaired so that there are no gaps or open spaces greater than _____ at the edge of the box.

Answer 16

1/8 in.

Question 17

Given: A rigid metal conduit (RMC) originates from a panelboard in an area that is unclassified, then passes through a Class I, Division 1 area, and then terminates in equipment that is also in an unclassified area. The RMC is without any connections or fittings except at the terminations. How many seal-off fittings are required in the RMC?

Answer 17

none

Question 18

Fill in the blank:

Given: The kitchen of a one family dwelling has three ovens rated 6, 8, and 3.5 kW; a cooktop rated 6 kW and a broiler rated 3.5 kW. The demand load, in kW, on the ungrounded feeder conductors for the cooking appliances serving the kitchen is _____ when applying the general method of calculations for dwellings.

Answer 18

12.2 kW

6 kW + 8 kW + 3.5 kW + 6 kW + 3.5 kW = 27 kW (connected load)

Column C, 5 appliances = 45% demand factor 27 kW x 45% = 12.12 kW demand load

Question 19

Fill in the blank:

Receptacles supplying power to freestanding-type office furnishings shall be located not more than _____ from the furnishing that is connected to it.

Answer 19

1 feet

Question 20

Fill in the blank:

For the purpose of determining conductor fill in a device box, the NEC mandates a switch to be counted as equal to two (2) conductors. The volume allowance for the two (2) conductors shall be based on the _____.

Answer 20

largest size wire connects to the switch.

Question 21

Fill in the blank:

A device or group of devices that serves to govern, in some predetermined manner, the electric power delivered to the apparatus to which it is connected is a _____.

Answer 21

controller

Question 22

Which of the following type motors are not approved for use in a Class, I Division 1 location?

a. Totally enclosed fan cooled motors.
b. Submerged motors in a liquid that is flammable only when vaporized.
c. Totally enclosed motors with positive-pressure ventilation.
d. Totally enclosed motors filled with inert gas.

Answer 22

d. totally enclosed fan cooled motors

Question 23

Fill in the blank:

Unless listed and identified otherwise, terminations and conductors of circuits rated 100 amperes or larger, shall be rated for _____.

Answer 23

75°C

Question 24

Determine the conductor ampacity where given the following related information:
• conductors are size 500 kcmil THWN copper
• ambient temperature is 125°F
• eight (8) current-carrying conductors are in the raceway

Answer 24

178.2 amperes

500 kcmil THWN copper ampacity before derating = 380 amperes

380 amps x .67 (temp. correction) x .7 (adj. factor) = 178.22 amperes

Question 25

# Fill in the blank: Receptacles incorporating an isolated grounding conductor connection intended for the reduction of electrical noise, shall be identified by a/an \_\_\_\_\_ located on the face of the receptacle.

Answer 25

orange triangle