Electrical Level 4 Module 1 Questions With 100%
Verified Complete Solution
Name one reason the current-carrying conductor size would be adjusted.
There are more than three current-carrying conductors in a raceway per NEC Section
310.15(B)(3)
Voltage drop rule of thumb (A)
VD for feeders should not exceed 3% to the farthest outlet and 5% for the combo of
feeders and branch circuits to the farthest outlet.
Voltage Drop rule of thumb (B)
When combined, the max VD allowed for the branch circuit is usually 3%, then VD
allowed for feeder can be no more than 2%.
What are the formulas to calculate VD for single-phase circuits with resistive
loads?
VD = 2xLxRxI/1,000 and VD = 2xLxKxI/CM
CM
Area of the conductor in circular mils
Continuous duty load
A load that operates without interruption for more than 3 hours straight
What is the adjusted ampacity for each of six No. 4/0 THHN copper current-
carrying conductors in a single conduit?
See NEC Table 310.15(B)(16) for ampacity and NEC Table 310.15(B)(3)(a) for adjusted
ampacity by 80%
1.732
The square root of 3
VD = square root 3xLxRxI/1,000
Formula for VD of a three-phase feeder with a noncontinuous load
I= VA/V x square root of 3 or I = VA/V x 1.732
Formula for balanced three-phase circuit feeder ampacity
When the overcurrent protection for a conductor is located at the load end
instead of at the supply side of a conductor
Verified Complete Solution
Name one reason the current-carrying conductor size would be adjusted.
There are more than three current-carrying conductors in a raceway per NEC Section
310.15(B)(3)
Voltage drop rule of thumb (A)
VD for feeders should not exceed 3% to the farthest outlet and 5% for the combo of
feeders and branch circuits to the farthest outlet.
Voltage Drop rule of thumb (B)
When combined, the max VD allowed for the branch circuit is usually 3%, then VD
allowed for feeder can be no more than 2%.
What are the formulas to calculate VD for single-phase circuits with resistive
loads?
VD = 2xLxRxI/1,000 and VD = 2xLxKxI/CM
CM
Area of the conductor in circular mils
Continuous duty load
A load that operates without interruption for more than 3 hours straight
What is the adjusted ampacity for each of six No. 4/0 THHN copper current-
carrying conductors in a single conduit?
See NEC Table 310.15(B)(16) for ampacity and NEC Table 310.15(B)(3)(a) for adjusted
ampacity by 80%
1.732
The square root of 3
VD = square root 3xLxRxI/1,000
Formula for VD of a three-phase feeder with a noncontinuous load
I= VA/V x square root of 3 or I = VA/V x 1.732
Formula for balanced three-phase circuit feeder ampacity
When the overcurrent protection for a conductor is located at the load end
instead of at the supply side of a conductor
