Make Electronics

Experiment 32: A Little Robot Cart

282 Chapter 5

FundAmentAls

Wire    gauges

If you’re going to power larger motors, or

other components that take more current than

LEDs or small relays, you really need to know

about wire gauges. In particular, what’s the

relationship between wire thickness and AWG

(American Wire Gauge)? And what gauge of

wire should you use for any given current?

You can find numerous charts and tables if you

go online, but many of these sources con-

tradict each other, especially on the topic of

how much current is safe to run through each

gauge of wire.

After making several comparisons (and testing

some wire samples myself), I’ve compiled the

table in Figure 5-103, which I recommend as a

compromise. Note the following:

• This table applies to solid-core copper
  wire.


• For stranded wire, or copper that has
  been tinned (giving it a silver appear-
  ance), the number of ohms per foot will
  increase, the number of feet per ohm will
  decrease, and the maximum amperage
  will decrease, probably by around 20%.
  The maximum amperage assumes that the
  wire is insulated, preventing it from radiating
  heat as effectively as a bare conductor. I am
  also assuming that the wire is likely to be at
  least partially enclosed, inside a box or cabi-
  net. At the amperages listed for each gauge of
  wire, you should expect the wire to become
  noticeably warm, and personally I would tend
  to use thicker wire instead of the maximums
  indicated in the table.
  Most tables of this type only tell you the resis-
  tance of each gauge of wire in ohms per 1,000
  feet. I have included that number but have
  also expressed the function the other way
  around, as the number of feet per ohm, as this
  doesn’t require you to do so much arithmetic
  with decimals.^30 0.010^10

28 0.013 15

26 0.016 25

24 0.02 39

22 0.025 62

20 0.032 99

18 0.04 157

16 0.051 249

14 0.064 396

12 0.081 630

10 0.102 1,000

8 0.128 1,590

7 0.144 2,010

6 0.162 2,510

5 0.182 3,190

4 0.204 4,020

3 0.229 5,080

2 0.258 6,400

1 0.289 8,070

0 0.325 10,200

00 0.365 12,800

000 0.41 16,200

0000 0.46 20,400

AWG

Diameter

in

inches

Feet

per

ohm

103.2

64.9

40.1

25.7

16.1

10.2

6.39

4.02

2.53

1.59

0.999

0.628

0.498

0.395

0.313

0.249

0.197

0.156

0.124

0.098

0.078

0.062

0.049

Ohms

per

1,000 ft

0.5

1.0

1.5

2.5

5

8

10

13

17

23

32

44

51

60

70

80

90

100

125

150

175

200

225

Maximum

amps

(insulated)

Figure 5-103. American wire gauges (AWG) and their properties.