Electrical Measurements.
Reading edition
The Paris Congress Units (1884) are now universally adopted and consist as follows:
Electro-motive Force, and Potential (E).—The Volt. The legal volt is ·926 of the E. M. F. of a Daniell’s cell, which for rough purposes may be taken as a volt.
Resistance (R).—The Ohm. The legal ohm is now represented by the resistance of a column of mercury of a square millimetre in section at the temperature of zero centigrade 1·062 metres long.
Current (C).—The Ampère. This is the strength of current sent through a wire having the resistance of 1 ohm at the E. M. F. of 1 volt.
Quantity (Q).—The Coulomb. It is the quantity of electricity given by an ampère in a second. One coulomb decomposes ·00142 grain of water.
Heat or Work (W).—The Joule, or Volt-Coulomb, is the work done by 1 coulomb in 1 ohm. The work done by any current per second is obtained in ergs by the product of the current into the electro-motive force producing it or W = CE or W = C²R. The Erg is the C. G. S. unit of work.
Power (P).—The Watt, 1 ÷ 746 of a horse-power, employed in doing 1 joule of work in 1 second.
HP, or the Horse-power, is found by dividing C E by 746, thus (CE)⁄₇₄₆ or (C²R)⁄₇₄₆ = HP.
See also explanation of terms.
ELECTRICAL TABLE OF THE BIRMINGHAM WIRE GAUGE FOR PURE COPPER.
B.W.G. No. Diameter in Inches. Diameter in Millimeters. Area in Square Inches. Circumference in Inches. Pounds per Mile. Feet per Pound Feet per Ohm. Ohms per 1000 Feet.
1 ·3 7·62 ·070686 ·94248 1444·0087 3·662 8706·843 ·1148
2 ·284 7·21 ·063347 ·89221 1291·8699 4·0988 7803·51 ·1282
3 ·259 6·58 ·052685 ·81367 1074·5697 4·9262 6490·09 ·1540
4 ·238 6·04 ·044488 ·74770 907·3683 5·850 5580·01 ·17007
5 ·22 5·59 ·038013 ·69115 773·045 6·83 4681·1 ·2136
6 ·203 5·16 ·032365 ·63774 657·205 8·02 3985·7 ·2509
7 ·180 4·57 ·025447 ·56549 517·493 10·20 3134·8 ·3190
8 ·165 4·19 ·021382 ·51836 434·861 12·14 2633·7 ·3797
9 ·148 3·76 ·017203 ·46495 349·853 15·10 2119·9 ·4719
10 ·134 3·40 ·014103 ·42097 286·651 18·44 1737·0 ·5757
11 ·120 3·05 ·011309 ·37699 229·997 22·95 1392·9 ·7179
12 ·109 2·77 ·009331 ·34243 189·763 27·82 1149·4 ·8700
13 ·095 2·41 ·007088 ·29845 144·144 36·63 873·1 1·1454
14 ·083 2·11 ·005411 ·26075 110·035 47·98 665·3 1·503
15 ·072 1·83 ·004071 ·22619 82·790 63·77 501·5 1·9941
16 ·065 1·65 ·003318 ·20420 67·478 78·25 408·7 2·4466
17 ·058 1·47 ·002642 ·18221 51·3163 102·89 310·8 3·2176
18 ·049 1·24 ·001886 ·15394 38·3486 137·68 232·3 4·3052
19 ·042 1·07 ·001385 ·13195 28·1741 187·40 170·6 5·8599
20 ·035 ·89 ·000962 ·10995 19·5677 269·83 118·5 8·4381
21 ·032 ·81 ·000804 ·10053 16·3574 322·79 99·1 10·094
22 ·028 ·71 ·000616 ·08796 12·5242 421·58 75·8 13·185
23 ·025 ·63 ·000491 ·07854 9·9845 528·82 60·5 16·539
24 ·022 ·55 ·000380 ·06911 7·7299 683·06 46·8 21·357
ELECTRICAL RESISTANCE OF COPPER WIRE IN FRENCH MEASUREMENTS.
B.W.G. No. Diameter in Millimetres. Area in Millimetres. Circumference in Millimetres. Metres per Kilogramme. Kilogrammes per Metre.
1 7.62 45.6 23.9 1ᵐ.95 0ᵏ.514
2 7.21 40.8 22.6 2.78 0.360
3 6.58 34 20.7 3.33 0.300
4 6.04 28.7 19 3.95 0.253
5 5.59 24.5 17.6 4.61 0.217
6 5.16 21 16.2 5.43 0.184
7 4.57 16.4 14.3 6.90 0.145
8 4.19 13.8 13.1 8.20 0.122
9 3.76 11.1 11.8 10.20 0.098
10 3.40 9.1 10.7 12.50 0.080
11 3.05 7.3 9.6 13.50 0.074
12 2.77 6 8.7 18.87 0.053
13 2.41 4.6 7.6 24.80 0.0403
14 2.11 3.5 6.63 32.40 0.0309
15 1.83 2.63 5.75 45.10 0.0232
16 1.65 2.14 5.18 52.90 0.0189
17 1.47 1.70 4.62 69.40 0.0144
18 1.24 1.21 3.90 94.30 0.0106
19 1.07 0.9 3.36 135.10 0.0074
20 0.89 0.62 2.80 181.8 0.0055
21 0.81 0.51 2.54 212.8 0.0047
22 0.71 0.39 2.23 285.7 0.0035
23 0.63 0.31 1.98 364 0.0028
24 0.55 0.24 1.73 465 0.00215
B.W.G. No. Resistance in Ohms Kilogrammes per Ohm. Metres per Ohm.
per Kilogramme. per Metre.
1 0.00073515 0.0003777 1360 2652
2 0.00116760 0.000420 860 2379
3 0.00168165 0.000505 595 1980
4 0.00232260 0.000588 430 1700
5 0.03227000 0.000700 310 1430
6 0.00452319 0.000833 220 1200
7 0.00731400 0.00106 137 945
8 0.01025000 0.00125 98 802
9 0.01581000 0.00155 63 646
10 0.0237500 0.00190 42.20 527
11 0.0318600 0.00236 31.40 424
12 0.0539682 0.00286 18.60 350
13 0.0932480 0.00376 19.70 266
14 0.160380 0.00495 6.26 202
15 0.294954 0.00654 3.40 153
16 0.430077 0.00813 2.30 123
17 0.73564 0.0106 1.35 94.5
18 1.33906 0.0142 0.75 70.4
19 2.60743 0.0193 0.38 51.9
20 5.05404 0.0278 0.20 36
21 7.04368 0.0331 0.14 30.2
22 12.37081 0.0433 0.08 23.1
23 19.6924 0.0541 0.05 18.5
24 32.5500 0.0700 0.03 14.3
For Table of English Measurements see page 105.