Unit 4: Conductor Ampacity and Sizing Flashcards
Learn ampacity tables, analyze temperature adjustments, and determine correct conductor sizing.
Fill in the blank:
Overcurrent protection for size 18 AWG non-power limited fire alarm (NPLFA) circuit conductors shall not exceed ________ and the overcurrent protection for size 16 AWG NPLFA circuit conductors shall not exceed ________.
7 amperes, 10 amperes
Fill in the blank:
The general rule is where raceways and cables are exposed to direct sunlight on or above rooftops, and the distance above the roof to the bottom of the raceway or cable is less than 7/8 in., a temperature adder of 33°C (60°F) shall be added to the outdoor temperature to determine the applicable ambient temperature for application of the correction factors. An exception to this rule is _______\__.
where the insulated conductors or cables are Type XHHW-2
Fill in the blank:
An emergency system is required to have NO more than, ________ to have power available in the event of failure of the normal supply system.
10 seconds
Fill in the blank:
X-ray equipment installed in a hospital may be served by a hard-service cord with a suitable attachment plug, provided the branch circuit rating does not exceed ________.
30 amperes
Fill in the blank:
Elevator driving motors used with a generator field control are rated as ________ duty motors.
intermittent
Fill in the blank:
Where a direct burial cable has a voltage of 45 kV, the NEC® mandates the MINIMUM burial depth of the cable to be at LEAST ________.
42 in.
Given: A recreational vehicle campground has a total of 150 RV campsites with electrical power. Twenty-five (25) of the campsites are reserved as tent sites.
How many sites are required to have at LEAST one (1) 20- ampere, 125-volt receptacle outlet?
150
Determine the MINIMUM size type SO cord permitted to supply a 40 hp, 460-volt, 3-phase, continuous-duty, ac wound rotor, motor installed in an area with an ambient temperature of 86 degrees F.
2 AWG
FLC of motor = 52 amperes x 125% = 65 amperes
Size 2 AWG SO cord with an ampacity of 80 amperes should be
selected.
Fill in the blank:
Where a 30 hp, 240-volt, 3-phase synchronous motor has a power factor of 90 percent, as per the NEC® the full load running current of the motor is ________.
69.3 amperes
63 amperes x 1.1 (power factor) = 69.3 amperes
Fill in the blank:
When water reaches the height of the established electrical datum plane for an irrigation pond, the on land electrical service equipment must ________.
disconnect
When installing an emergency battery pack lighting unit, what requirement must be met regarding the branch circuit that supplies power to the equipment, disregarding any exceptions?
It must be on the same branch-circuit serving the normal lighting in the area.
In an industrial establishment, what is the MAXIMUM length of 200 ampere rated busway that may be tapped to a 600 ampere rated busway without providing additional overcurrent protection?
50 feet
Fill in the blank:
Size 4/0 AWG, 75 deg. C aluminum secondary conductors of a 3-phase delta-wye transformer, shall be protected at not more than ________.
200 amperes
Size 4/0 AWG AL conductors rated @ 75 deg. C ampacity = 180 amperes
Next standard size OCP is rated at 200 amperes.
NOTE: Sec. 240.4(F) requires secondary OCP on delta-wye transformers.
Fill in the blank:
For trade size 3/4 in. MI cable, the radius of the inner edge of the bend shall NOT be less than ________ times the external diameter of the cable.
five
Fill in the blank:
Where an exposed flat cable assembly, Type FC, is installed LESS than ________ above the floor or fixed working platform, it shall be protected by a cover identified for the use.
8 feet
Fill in the blank:
The MINIMUM burial depth for conduit or cables installed under an airport runway, concourse or tarmac is ________.
1½ feet
Determine the MINIMUM size overload protection required for a 480 volt, 3-phase, 15 hp, continuous-duty motor given the following related information:
- Design C
- temperature rise - 40 deg. C
- service factor - 1.12
- actual nameplate rating - 18 amperes
20.7 amperes
FLA of motor = 18 amps x 115% = 20.7 amperes
Assume where the overload protection you have selected on the above motor is not sufficient to start the motor and trips, therefore, modification of this value is necessary, determine the MAXIMUM size overload protection permitted.
23.4 amperes
FLA of motor = 18 amps x 130% = 23.4 amperes
Where a 50 kVA transformer with a 480-volt, 3 phase primary and a 208Y/120-volt, 3-phase secondary is to be installed and overcurrent protection is required on both the primary and secondary side of the transformer; determine the MAXIMUM size overcurrent protection device permitted for the primary side.
150 amperes
I = kVA x 1,000/E x 1.732 = 50 x 1,000/480 x 1.732 = 50,000 VA/831.36 = 60.2 amperes
60.2 amperes x 250% = 150.5 amperes
What is the demand load, in VA, for the general-use receptacles in an office building that has a total of 150 general-use, 125-volt, 20-ampere, single-phase receptacle outlets installed?
18,500 VA
150 receptacles x 180 VA = 27,000 VA
1st. 10,000 VA @ 100% = 10,000 VA
(remainder) 17,000 VA @ 50% = 8,500 VA
TOTAL DEMAND = 18,500 VA
Determine the MAXIMUM number of size 12 AWG conductors permitted to be housed in a 3½ in. deep, 3-gang masonry box that contains three (3) switches.
21
[masonry box] 9 (Size 12 AWG conductors permitted per gang) - 2 conductors per gang (switch) 7 wires per box x 3 gang = 21 conductors
Fill in the blank:
A horizontal raceway entering a dust-ignition proof enclosure from one that is not, need not have a seal-off if it is at LEAST ________ in length.
10 feet
What requirement must be met for tags on abandoned communications cables that are identified for future use?
It must be of sufficient durability to withstand the environment.
Fill in the blank:
All 125-volt, 15- and 20-ampere receptacles located within ________ of the inside walls of a storable pool, storable spa, or storable hot tub shall be protected by a ground fault circuit interrupter.
20 feet
