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Wire Types and Sizes
16 questions By Tony R. Kuphaldt
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Question 13 of 16
Determine the cross-sectional area of these conductors (viewed from one end), in units of “square inches” as well as “circular mils”:
Reveal answerFrom left to right:
XXXXXXXX XXXXXXX XXXXXXX 0.049 in2 0.008 in2 2.0 in2 62,500 cmil 10,384 cmil 2,546,479 cmil Notes:Calculating the cross-sectional area of the 1 ×2 busbar in units of circular mils may be challenging for some students, because an equation directly relating linear dimensions to circular mil area may not be easy to obtain. However, even in the event that no equation can be found, there is a way to solve for the busbar’s area in units of circular mils by observing the answers obtained for the other two conductors’ areas.
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Question 14 of 16
Small electrical wires are almost always sized by gauge rather than by circular mils (cmils). So, if you had to calculate the resistance of a length of 22-gauge copper wire and did not have the proper tools to measure the wire’s diameter, how could you find the equivalent cross-sectional area in circular mils so as to use the equation R = [(ρl)/A]?
Reveal answerThis information may be found in a wire gauge table, where gauge numbers and circular mil values are cross-referenced.
Notes:Show your students a wire gauge table, if their textbooks do not already contain one.
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Question 15 of 16
If an electric drill is plugged into a very long extension cord instead of being plugged directly into a power receptacle, what will happen to the drill’s performance? Explain your answer, with reference to Ohm’s Law.
Reveal answerThe drill will not perform with as much power as it would if directly plugged into a power receptacle.
Challenge question: draw an equivalent schematic diagram showing the resistance of the extension cord conductors as resistors with the labels Rwire1 and Rwire2.
Notes:Students who have worked with power tools, especially on construction sites where long extension cords are commonly used, will be familiar with this phenomenon. Ask your students what effect different gauges of wire in the extension cord would have on this degradation of drill motor performance. Also, ask about different lengths of extension cord. What, exactly, is the electrical quantity that varies with these dimensional changes, that causes the drill motor performance to vary?
