Exam (elaborations)
26401 Load Calculations - Feeders And Services: Q&A
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26401 Load Calculations - Feeders And Services: Q&A
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26401 Load Calculations - Feeders And Services: Q&ALoad calculated at 2 circuit 1500VA. Right Ans - Small Appliance Ciruit
Voltage drop formula 1
VD = (2*L*R*I)/1,000 Right Ans - VD = voltage drop (in volts)
L = load center or total length in feet
R = conductor resistance per NEC Chapter 9, Table 8
I = current
The number 1,000 represents 1,000' or less of conductor.
Show window loads should be calculated at _____ per linear foot of show
window. Right Ans - 200VA
What is the minimum demand required for the portion of a feeder that
supplies 30' of show windows?
6,000 VA
5,400 VA
3,000 VA
2,700 VA Right Ans - ft x va = va
30ft x 200VA = 6,000VA
NEC 220.14(C)(2)
At 200 Volt-amperes per linear 300 mm (1 ft) of show window
Voltage drop formula 2
VD = (2*L*K*I)/CM Right Ans - VD = voltage drop
L = load center or total length in feet
K= constant (12.9 for copper conductors; 21.2 for aluminum conductors)
I = current
CM= area of the conductor in circular mils (from NEC Chapter 9, Table 8)
Feeder conductor size is adjusted when?
The load supplied is a continuous-duty load.
More than three current-carrying conductors are in a raceway.
The ambient temperature surrounding conductors exceeds temperature
ratings.
, Voltage drop exceeds 3% for feeders or 5% for the combination of the feeder
and branch circuit.
All of the above Right Ans - All of those above
In calculating feeder-circuit conductors, if noncontinuous loads equal 450
amperes and continuous loads equal 550 amperes, what is the total calculated
feeder load that the conductors must handle?
A. 1137.50 amperes
B. 1100 amperes
C. 950 amperes
D. 1317.50 amperes Right Ans - In order to calculate the total feeder load,
you must add 100% of noncontinuous loads to 125% of continuous loads.
450 + (1.25 × 550) = 1137.50 amperes
Using the 25' tap rule, what is the minimum size copper THWN conductor
required for a tap from a 400A, 480V, 3Phase feeder?
1/0
2/0
No. 1
No. 2 Right Ans - 1/0
Which of the following factors does not affect conductor ampacity
adjustments?
A. Ambient temperature
B. Number of phases
C. Continuous or noncontinuous load
D. Number of conductors in a raceway Right Ans - The number of phases is
not listed as a factor that affects the allowable current-carrying capacity
(ampacity) of a conductor, while the others listed do affect it.
Switchboard Right Ans - A large single panel, frame, or assembly of panels
on which are mounted on the face, back, or both, switches, overcurrent and
other protective devices, buses, and usually instruments. Switchboards are
generally accessible from the rears well as from the front and are not intended
to be installed in cabinets.
If a single-family dwelling has 1,350 sq ft of living area, two small-appliance
circuits in the kitchen, and one laundry room receptacle, what is the calculated
net lighting and small appliance load, including the laundry room circuit,
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