Specifications
20
Table 2.3 A sample of gauge No.s and its equivalent are given in the following table.
10 Two runs of 13 SWG 19 Two runs of 22 SWG
12 Two runs of 15 SWG 19 Two runs of 25 SWG
14 Two runs of 17 SWG 19 Two runs of 27 SWG
17 Two runs of 20 SWG 19 Two runs of 28 SWG
Standard
Gauge Number
Equivalent Gauge
Number and runs
Standard Gauge
Number
Equivalent Gauge
Number and runs
2. Area of Cross-section of one particular wire gauge number is two times more than that
of gauge number, when increased by three. For example area of cross-section for 17
gauge wire is approximately two times more than that of 20 gauge wires. If 17 gauge
wire is not available then we use two 20 gauge wires.
3. When 20 gauge and 17 gauge wires are used for particular length, then the weight of
17 gauge wire is double as that of the weight of the 20 gauge wire, because weight is
directly proportional to the area of cross-section of the wire.
4. Resistance of the winding wire is indirectly proportional to the cross-sectional area of
the wire. Therefore, the resistance of 17 gauge wire is half of the resistance value of 20
gauge wire.
5. Resistance of winding is measured in two methods.
(i) By using multimeter, the resistance of the winding is directly measured in ohms
or kilo ohms.
(ii) 15 to 20% value of the rated voltage is applied by using auto transformer to each
phase of three phase winding. Then current in each phase is measured and then
the resistance of the winding is calculated.
Table 2.4 Resistance value of Copper and Aluminum wires
Cross
sectional
area mm
2
Cross
sectional
area inch
2
Approx
S.W.G
No.
Copper
wt.kgm
per km
Resistance
ohm/ km.
at 20
0
C
Aluminum
weight
Kgm / km
Resistance
at 20
0
C
ohm/km
1 mm
2
0.00155 18 8.89 17.86 2.7 30.3
1.5 mm
2
0.00230 17 13.34 11.91 4.04 20.2
2.5 mm
2
0.0038 15 22.33 7.144 6.74 12.12
4 mm
2
0.0062 13 35.56 4.46 10.8 7.575
6 mm
2
0.0093 11 53.34 2.977 16.2 5.05
10 mm
2
0.0155 9 88.90 1.786 27 3.03
2.8 GAUGE PLATE: The sizes of wire are estimated by a device, called gauges, which consist
of plates of circular or oblong form having notches of different widths around their edges. Each
notch is stamped with a number, and the wire which just fits a given notch, is stated to be of,
say, No. 10, 11, 12, etc., of the wire gauge.