Lesson 4: Finalizing Ampacity Calculations Flashcards
Drag the words into the blanks to complete the statement below.
The ____ rating associated with the _____ of a conductor shall be selected and coordinated so as not to exceed the _____ temperature rating of any connected _____, conductor, or device.
temperature, ampacity, lowest, termination.
Where different temperature limitations of individual components are applied to a single circuit, the principle of the ? is often used to determine the temperature rating of the entire circuit.
a.
chain reaction
b.
skin effect
c.
strong will survive
d.
weakest link
d. weakest link
NEC ? requires that electrical equipment be installed and used according to any instructions included with the equipment’s listing or labeling.
a.
110.26(A)
b.
110.3(B)
c.
240.4(B)
d.
310.16
b.
110.3(B)
NEC Article 100 permits a 75°C conductor to be used with equipment marked 60°C, provided the ampacity of the 75°C conductor is taken from the ? column of Table 310.16.
a. 60°C
b. 75°C
c. 90°C
d. 150°C
a. 60°C
110.14(C)(1)(a)(2)
which of the following lighting loads would NOT generally be considered a continuous load?
a. commercial office space lighting
b. residential lighting
c. retail show window lighting
d. retail store lighting
b. residential lighting
NEC: article 100
a load where the maximum current is expected to continue for 3 hours or more would be defined as ____?
a. continuous duty
b. continuous load
c. intermittent duty
d. uninterrupted
b. continuous load
NEC: article 100
which of the following loads would generally be considered a continuous load? select all that apply
a. fixed electric space heating equipment
b. fixed electric space heating equipment for pipelines and vessels
c. fixed outdoor electric deicing equipment
d. fixed storage type water heater with a 100 gallon capacity
all of them
see NEC: 422.13, 424. 4 (B), 426.4 and 427.4
which of the following loads would generally be considered a continuous load?
a. a refrigerator
b. an electric clothes dryer
c. an electric range
d. an electric sign installed at the front of a retail store
d. an electric sign installed at the front of a retail store
see NEC: Article 100 and 600.5(C)
A 4/0 AWG THHN aluminum conductor is connected to a 200-ampere rated circuit breaker with an unknown temperature rating. What is the ampacity of this conductor when terminated to this circuit breaker?
180 A
see NEC: 110.14(C)(1)(A)(2)
A 12 AWG THWN-2 copper conductor is connected to a circuit breaker with termination temperature limitation marked 60 C/75 C. what is the ampacity of this conductor when terminated to this circuit breaker?
25 A
See NEC: 110.14(C)(1)(a)(3)
a 14 AWG THW copper conductor is connected to a motor marked with design letter B. what is the ampacity of this conductor when terminated to the motor?
20 A
see NEC: 110.14(C)(1)(a)(3)
a 14 AWG THW copper conductor is connected to a motor marked with design letter B. what is the ampacity of this conductor when terminated to the motor?
20 A
see NEC: 110.14(C)(1)(a)(4)
what minimum size THHN feeder circuit conductors are required for a circuit when it supplies 80 amperes of continuous load and 40 amperes of noncontinuous load? the equipment terminations have a temperature rating of 75 degrees C.
a. 2 AWG
b. 1 AWG
c. 1/0 AWG
d. 2/0 AWG
c. 1/0 AWG
215.2(A)(1)
What minimum size THW branch circuit conductors are required for a circuit when it supplies a 240-volt, 4-kilowatt electric baseboard heater? The equipment terminations have an unknown temperature rating.
a. 14 AWG
b. 12 AWG
c. 10 AWG
d. 8 AWG
c. 10 AWG
424.4(B)
P/E=I
4000/240=16.67 A
16.67x1.25=20.8375 A
Table 310.16 10 THW out of the 60 degrees C column has an ampacity of 30 A.
what is the minimum size THWN-2 feeder circuit conductors are required for a 480 volt, 3-phase circuit when it supplies 50 Kilowatts of continuous load and 10 kilowatts of noncontinuous load? The equipment terminations have an unknown temperature rating.
a. 3 AWG
b. 2 AWG
c. 1/0 AWG
d. 2/0 AWG
b. 2 AWG
215.2(A)(1)
(50 kW x 1.25) + 10 kW = 72.5 kW
72,500 W / (480x1.732) = 87.21 A
Table 310.16
2 AWG THWN-2 out of the 60 degrees C column has an ampacity of 95 A
What is the minimum size THW branch circuit conductor permitted to be protected by the following overcurrent protection device when all equipment is listed at 75 degrees C and the conductors do not supply more than one receptacle?
50 A
Choose…
90 A
Choose…
150 A
Choose…
225 A
Choose…
300 A
Choose…
50 A = 8 AWG THW
90 A = 4 AWG THW
150 A = 1 AWG THW
225 A = 4/0 AWG THW
300 A = 250 kcmil
NEC: 240.4(B) and table 310.16
A 480-volt, 3-phase circuit supplies a 50-kilowatt continuous load and a 10-kilowatt noncontinuous load. What is the minimum standard size inverse-time circuit breaker?
90 A
NEC: 210.20 and 215.3
(50 kw x 1.25) + 10 kW = 72.5 kW
72,500 W / (480 x 1.732) = 87.2 A
up to the next standard size OCPD of 90 A from table 240.6(A)
A 120-volt circuit supplies 38 amperes of continuous load. What is the minimum standard size fuse required for overcurrent protection of the circuit?
50 A
NEC: 210.20
38 A x 1.25 = 47.5 A
Table 240.6(A) bumps up to 50 A
A 240-volt single phase circuit supplies a 5 kW continuous load and 6 kW noncontinuous load. what is the minimum standard size inverse time circuit breaker?
60 A
NEC 210.20 and 215.3
(5000 x 1.25)+6000= 12,250 W
12,250W/240= 51.04 A
bump up to next standard size OCPD out of table 240.6(A) 60 A
What is the maximum standard size overcurrent protective device permitted to protect the following THW conductors when they are not part of a branch circuit supplying more than one receptacle and are terminated to equipment rated 75°C?
6 AWG THW
2/0 AWG THW
4/0 AWG THW
350 kcmil THW
600 kcmil THW
The correct answer is: 6 AWG THW → 70 A, 2/0 AWG THW → 175 A, 4/0 AWG THW → 250 A, 350 kcmil THW → 350 A, 600 kcmil THW → 450 A
Note: See NEC 240.4(B) and Table 240.6(A).
A 120/208-volt, 3-phase feeder supplies continuous load of 37.5 kVA, consisting of computers and other nonlinear loads. the feeder is installed in a RMC, in an area with an ambient temperature of 95 degrees F. what is the minimum standard size OCPD required?
a. 100 A
b. 110 A
c. 125 A
d. 150 A
d. 150 A
NEC: 215.3
37.5 kVA x 1.25 = 46.88 kVA
46,880 VA / (208x1.732) = 130.13 A
round up to next standard size OCPD in table 240.6(A) 150 A
A 120/208-volt, 3-phase feeder supplies continuous load of 37.5 kVA, consisting of computers and other nonlinear loads. the feeder is installed in a RMC, in an area with an ambient temperature of 95 degrees F. what minimum size ungrounded THHN conductors are required for the feeder?
a. 2 AWG
b. 1 AWG
c. 1/0 AWG
d. 2/0 AWG
b. 1 AWG
215.2
37,500 VA / (208 x 1.732) = 104.09 A
104.09 x 1.25 = 130.11 A
table 310.16
1 AWG has the ampacity of 130 A out of the 75 degree C column
215.2(A)(2)
1 AWG 145 A x .96 x .8 = 111.36 A is sufficient load of 104.09 A
A 480-volt, 3- phase feeder supplies 85 amps of cont. load and 50 amps of noncont. load.
the feeder is installed in RMC in an area with an ambient temperature of 123 degrees F. what minimum size ungrounded THWN conductors are required for the feeder?
a. 2/0 AWG
b. 3/0 AWG
c. 4/0 AWG
d. 250 kcmil
d. 250 kcmil
NEC: 215.2
(85 x 1.25)+50= 156.25
A 480-volt, 3- phase feeder supplies 85 amps of cont. load and 50 amps of noncont. load.
the feeder is installed in RMC in an area with an ambient temperature of 123 degrees F. what minimum standard size overcurrent protective device is required for the feeder?
175 A
215.3
(85 x 1.25)+50= 156.25
round up to next standard size OCPD 175 A out of 240.6(A)
a load where the maximum current is expected to continue for 3 hours or more would be defined as continuous duty.
true or false
False
from a practical point of view, after the cont. load and noncont. loads are calculated, the size of the circuit conductors should be determined first and the size of the OCPD should be selected second.
true or false
False
