Concept explainers
In problem 35, it is desired to keep the voltage drop to 3% maximum. What minimum size wire would be installed to accomplish this 3% maximum voltage drop? See 210.19(A), Informational Note No. 4 and 215.2(A)(1), Informational Note No. 2.
Find the minimum size wire that should be installed to accomplish 3% maximum voltage drop.
Answer to Problem 36R
10 AWG or larger value conductor should be installed to accomplish 3% maximum voltage drop.
Explanation of Solution
Given data:
Supply voltage is 120-volt.
Current is 10 A.
The distance between panel and heater is approximately 140 ft.
14 AWG, 12 AWG, 10AWG, and 8 AWG copper conductor.
Calculation:
Write the expression for voltage drop in a single-phase circuit.
Here,
K is the approximate resistance in ohms per circular-mil foot at
I is the current, and
CMA is cross-sectional area of the conductors.
Modify Equation (1) for 14 AWG copper wire.
Refer TABLE 4-7 in the textbook for circular mil area (CMA) for many of the common conductors.
The value of CMA for 14 AWG is 4110.
Substitute
Modify Equation (1) for 12 AWG copper wire.
Refer TABLE 4-7 in the textbook for circular mil area (CMA) for many of the common conductors.
The value of CMA for 12 AWG is 6530.
Substitute
Modify Equation (1) for 10 AWG copper wire.
Refer TABLE 4-7 in the textbook for circular mil area (CMA) for many of the common conductors.
The value of CMA for 10 AWG is 10,380.
Substitute
Modify Equation (1) for 8 AWG copper wire.
Refer TABLE 4-7 in the textbook for circular mil area (CMA) for many of the common conductors.
The value of CMA for 8 AWG is 16,510.
Substitute
Tabulate the calculated value of the voltage drop as shown in Table 1.
Table 1
Sl. No. | Conductor Size | Voltage drop |
1 | 14 AWG | |
2 | 12 AWG | |
3 | 10 AWG | |
4 | 8 AWG |
Find the value of
Compare the obtained value of 3% voltage drop of applied voltage with voltage drops of each conductor as tabulated in Table 1.
A voltage drop of 8AWG conductor (that is 2.19 Volts drop) is less than
Conclusion:
Thus, 10 AWG or larger value conductor should be installed to accomplish 3% maximum voltage drop.
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