Unit 5: Box and Raceway Sizing

Question 1

Fill in the blank:

In Class II, Division 1 locations, where pendant mounted luminaires are suspended by rigid metal conduit (RMC) or intermediate metal conduit (IMC) and a means for flexibility is not provided, the conduit stems shall have a length of not more than ________.

Answer 1

12 in.

Question 2

Fill in the blank:

All hydromassage bathtub metal piping systems and all grounded metal parts in contact with the circulating water associated with the bathtub shall be bonded together using a solid copper bonding jumper not smaller than ________.

Answer 2

8 AWG

Question 3

Fill in the blank:

Where power-limited fire alarm (PLFA) circuit conductors pass through a wall or floor, the conductors shall be protected by a metal raceway or nonmetallic conduit up to a height of at LEAST ________ above the floor, unless other means of protection is provided.

Answer 3

7 feet

Question 4

Fill in the blank:

Luminaires installed in exposed or concealed locations under metal-corrugated sheet roof decking shall be installed and supported so there is not less than ________ clearance from the lowest surface of the roof decking to the top of the luminaire.

Answer 4

1 ½ in.

Question 5

Fill in the blank:

Transformers with ventilation openings shall be installed so the ventilating openings are not blocked by walls or other obstructions. The required clearances shall be ________.

Answer 5

clearly marked on the transformer

Question 6

Fill in the blank:

Where a one-family or two-family dwelling unit has a three (3) car attached garage, the NEC® requires a MINIMUM of ________ 125-volt, single-phase, 15- or 20-ampere receptacles to be installed in the garage.

Answer 6

three

Question 7

Fill in the blank:

With respect to messenger-supported service-drop conductors and open overhead wiring operating at 0 to 750 volts to ground, the MINIMUM vertical clearance that must be maintained from the base of a swimming pool diving board and the conductors is ________.

Answer 7

22 ½ feet

Question 8

Determine the MINIMUM required size 75 deg. C rated conductors permitted to be used to supply a demand load of 200 amperes where provided with a 208Y/120-volt, 3- phase 4-wire, electrical system. Consider all four (4) conductors to be current-carrying and the ambient temperature is 120 deg. F.

Answer 8

400 kcmil

200 amperes (load)/ .75 (temp. cor.) x .8 (adj. factor) = 200 = 333 amperes/ .6
Size 400 kcmil conductors with an ampacity of 335 amperes
should
be selected from Table 310.16.

Question 9

Fill in the blank:

A metal junction box to be installed will contain the following conductors:

• three - size 6 AWG ungrounded conductors
• three - size 6 AWG grounded conductors
• one size 8 AWG grounding conductor
• three - size 12 AWG ungrounded conductors
• three - size 12 AWG grounded conductors
• one - size 12 AWG grounding conductor

The junction box is required to have a volume of at LEAST ________.

Answer 9

46.50 cubic in.

6 AWG ungrounded conductors - 3 x 5.00 cu. in. = 15.00 cu. in.
6 AWG grounded conductors - 3 x 5.00 cu. in. = 15.00 cu. in.
8 AWG grounding conductor - 1 x 3.00 cu. in. = 3.00 cu. in.
12 AWG ungrounded conductors - 3 x 2.25 cu. in. = 6.75 cu. in.
12 AWG grounded conductors - 3 x 2.25 cu. in. = 6.75 cu. in.
12 AWG grounding conductor - 1 x -0- cu. in. = -0- cu. in.
TOTAL = 46.50 cu. in.

Question 10

Fill in the blank:

In regard to permanently installed swimming pools, where necessary to employ flexible connections to a pool pump motor, ________ shall be permitted as the wiring method(s).

I. UF cable
II. liquidtight flexible metal conduit (LFMC)

Answer 10

II only

Question 11

Fill in the blank:

In regard to legally required standby systems, transfer switches shall be ________ and marked for emergency system or legally required standby use and approved by the authority having jurisdiction.

Answer 11

automatic

Question 12

Fill in the blank:

In commercial vehicle repair garages, lamps and lampholders for fixed lighting located over lanes through which vehicles are commonly driven, shall be located not less than ________ above the floor level, unless the luminaires are of the totally enclosed type.

Answer 12

12 feet

Question 13

Determine the maximum permitted operational setting of an adjustable inverse time circuit breaker used for branch-circuit, short-circuit and ground-fault protection of a 10 hp, 208-volt, 3-phase, squirrel cage, Design B, continuous-duty motor. Assume the motor will start at this setting and exceptions are not applicable.

Answer 13

77.0 amperes

FLC of 10 hp motor = 30.8 amperes x 250% = 77 amperes

Question 14

Fill in the blank:

Where transformer vaults are not protected with an automatic fire-suppression system, they shall be constructed of approved materials that have a MINIMUM fire-resistance rating of ________.

Answer 14

3 hours

Question 15

Fill in the blank:

At a truck plaza, every electrified truck parking space intended to provide an electrical supply for transport refrigerated units (TRUs), shall be equipped with a ________ receptacle outlet.

I. 30 ampere, 480-volt, 3-phase, 3-pole, 4-wire
II. 60 ampere, 208-volt, 3-phase, 3-pole, 4-wire

Answer 15

either I or I

Question 16

What is the MAXIMUM distance allowed to support intermediate metal conduit (IMC) from a junction box, where structural members do not readily permit fastening?

Answer 16

5 feet

Question 17

Fill in the blank:

All signs provided with electric power shall be installed at a height of not less than _______\__ above areas accessible to vehicles unless protected from physical damage.

Answer 17

14 feet

Question 18

Fill in the blank:

Photovoltaic equipment shall be provided with isolating devices or equipment disconnecting means in circuits connected to equipment at a location within the equipment, or within sight and within ________ of the equipment.

Answer 18

10 feet

Question 19

Determine the MAXIMUM standard size inverse time circuit breaker permitted for branch circuit, short-circuit, and ground-fault protection for a 50 hp, ac motor, when given the following related information.

• continuous-duty
• induction type
• 3-phase, 480-volt
• Design L
• nameplate rating 62 amperes

Answer 19

250 amperes

FLC of 50 hp motor = 65 amperes x 400% = 260 amperes

Question 20

Fill in the blank:

In general, on the load side of the point of grounding of a separately derived system such as a transformer, a grounded conductor is not permitted to be connected to ________.

Answer 20

any of these

Question 21

Fill in the blank:

The life safety branch of the essential electrical system of a health care facility shall provide power to ________.

I. automatic doors used for building egress
II. illumination of electrical equipment rooms

Answer 21

I only

Question 22

Fill in the blank:

Intrinsically safe apparatus, associated apparatus, and other equipment shall be installed ________.

Answer 22

in accordance with the control drawings

Question 23

Fill in the blank:

The grounded conductor of a 3-phase, 3-wire, delta service shall have an ampacity not less than ________.

Answer 23

that of the ungrounded conductors

Question 24

Fill in the blank:

Where a 150 kVA service transformer has a 480Y/277- volt, 3-phase primary and a 208Y/120- volt, 3-phase secondary, the full-load ampere rating on the primary side of the transformer is ________.

Answer 24

180 amperes

I = kVA x 1,000/E x 1.732
= 150 x 1,000/480 x 1.732
= 150,000/831.36
= 180.32 amperes

Question 25

# Fill in the blank: Direct-buried cables or conductors located in a trench below 2 inch thick concrete or equivalent shall have a MINIMUM cover requirement of \_\_\_\_\_\_\_\_.

Answer 25

18 in.