American wire gauge numbering

Aviation Mechanic Powerplant (AMP) practice question 13 of 13 on Engine Electrical Systems. ACS element AM.III.F.K7 · difficulty: recall. Want to answer it in a timed quiz? Use the Aviation Mechanic Powerplant (AMP) practice mode.

Question bank updated 2026-09-22

QUESTIONUnder the American wire gauge (AWG) standard used for aircraft wire, how does conductor diameter relate to the gauge number?

ADiameter increases steadily as the number gets larger.
BGauge numbers show only the strand count.
CDiameter decreases as the number gets larger.

Show the answer and explanation

Correct answer: C. Diameter decreases as the number gets larger.

A — incorrect This reverses the standard; a number 40 wire is the smallest commonly used size, not the largest.
B — incorrect Gauge numbers compare conductor diameter; strand count enters only when the total area of a stranded wire is found by multiplying one strand's area by the number of strands.
C — correct The handbook states that under the AWG standard the wire diameters become smaller as the gauge numbers become larger, with number 0000 the largest commonly used size and number 40 the smallest.

BACKGROUND

Aircraft wire is manufactured in sizes according to the American wire gauge (AWG) standard, in which wire diameters become smaller as the gauge numbers become larger. The largest commonly used size is number 0000 and the smallest is number 40; larger and smaller sizes are manufactured but are not commonly used. Size can be checked with a wire gauge that reads from number 0 to number 36: the bare wire is inserted in the smallest slot that just accommodates it, and that slot's number is the wire size. The semicircular opening at the end of each slot is only there to let the wire move through and must not be mistaken for the measuring slot. Not every wire or cable can be measured accurately this way, since large wires are usually stranded to increase flexibility.

STUDY TIP

Remember one anchor pair, 0000 as the largest and 40 as the smallest, and the direction of the numbering never gets confused.

KEY POINTS

Larger AWG numbers mean smaller conductor diameters.
Number 0000 is the largest and number 40 the smallest commonly used size.
A wire gauge reads the size from the smallest slot that fits the bare wire.

SOURCES

amp-powerplant/ch04.txt "Wire Size"

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