Unit 5: Box and Raceway Sizing Flashcards
Evaluate box fill calculations, analyze raceway sizing factors, and apply NEC 2023 guidelines for compliance.
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 _________.
12 in.
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 _________.
8 AWG
Fill in the blank:
Where power-limited fire alarm (PLFA) circuit conductors pass through 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.
7 feet
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 no less than _________ clearance from the lowest surface of the roof decking to the top of the luminaire where the sheet metal is not covered with 2 inches of concrete.
1½ in.
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 _________.
clearly marked on the transformer
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.
three
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 _________.
22½ feet
200 amperes (load)/.75 (temp. cor.) x .8 (adj. factor) .6 = 200 = 333 amperes
Size 400 kcmil conductors with an ampacity of 335 amperes
should be selected from Table 310.16.
Determine the required size 75 deg. C rated conductors 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.
400 kcmil
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.
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 _________.
46.50 cubic in.
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)
II only
Fill in the blank:
For legally required standby systems, the transfer switches shall be _________ and marked for emergency system or legally required standby used and approved by the authority having jurisdiction.
automatic
Fill in the blank:
In commercial vehicle repair garages, lamps and lamp holders 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.
12 feet
Determine the initial 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 without tripping the circuit breaker.
77.0 amperes
FLC of 10 hp motor = 30.8 amperes x 250% = 77 amperes
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 _________.
3 hours
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
either I or II
What is the maximum distance allowed to support intermediate metal conduit (IMC) from a junction box where structural members do not readily permit fastening?
5 feet
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 _________.
14 feet
Fill in the blank:
Where conductors of solar photovoltaic (PV) systems are exposed to ambient temperatures greater than 30°C (86°F), the ampacities of these conductors shall be corrected in accordance with Table _________ of the Code.
690.31(A)(3)(2)
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.
250 amperes
FLC of 50 hp motor = 65 amperes x 400% = 260 amperes
In general, where is a grounded conductor not permitted to be connected on the load side of the point of grounding in a separately derived system, such as a transformer?
- equipment grounding conductors
- normally noncurrent-carrying metal parts of equipment
- ground the earth
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
I only
Fill in the blank:
Intrinsically safe apparatus, associated apparatus, and other equipment shall be installed in accordance witht the _________.
control drawings
Fill in the blank:
The grounded conductor of a 3-phase, 3-wire, delta service shall have an ampacity not less than _________.
that of the ungrounded conductors
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 _________.
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
