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Wire Types and Sizes
16 questions By Tony R. Kuphaldt
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Question 7 of 16
What is meant by the ampacity rating of a wire? What criteria establish the ampacity rating of any given wire?
Reveal answerThe “ampacity” of a wire is its maximum rated current. I won’t tell you what criteria establish the “ampacity rating of a wire, but I will say that you will find the characteristics of the insulation coating a wire has as much to do with a wire’s ampacity as the physical characteristics of the metal itself!
Notes:Be sure to ask your students what resource(s) proved helpful in researching the answer to this question. Being essentially a safety issue, there are several industry publications on electrical safety regulations that may prove informative.
This question connects several important principles together: physical ratings of materials, power dissipation in metallic conductors, and electrical safety. Challenge your students to “connect” these principles on their own by probing their knowledge with follow-up questions.
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Question 8 of 16
Examine the following American Wire Gauge table. Please note that most of the odd-numbered gauges have been omitted because the even-numbered gauges tend to be more common:
Gauge # Diameter (inches) Area (circular mils)
4/0 0.4600 211,600
3/0 0.4100 168,100
2/0 0.3650 133,225
1/0 0.3250 105,625
1 0.2890 83,521
2 0.2580 66,564
4 0.2040 41,616
6 0.1620 26,244
8 0.1280 16,384
10 0.1020 10,404
12 0.0810 6,561
14 0.0640 4,096
16 0.0510 2,601
18 0.0400 1,600
20 0.0320 1,024
22 0.0253 640.1
How many gauge numbers must you increase to (approximately) double the diameter of any given wire gauge? What effect does the doubling of diameter have on the cross-sectional area of the wire?Reveal answerWire diameter approximately doubles once for every six wire gauge sizes. Cross-sectional area quadruples for the same wire gauge interval.
Notes:Wire gauge numbers and diameters for this table were taken from table 2-85 of the American Electrician’s Handbook (eleventh edition) by Terrell Croft and Wilford Summers. Area in circular mils for each AWG size was calculated from the given diameter.
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Question 9 of 16
How many gauge American Wire Gauge sizes must you increase to (approximately) double the ampacity of any given wire gauge?
Reveal answerThe “rule of thumb” here is that a change of three gauge sizes will either double or halve the ampacity, depending on which way the gauge size changes.
Notes:Although this rule is only approximate, it is useful to know!
