Substituting (2) in (1)
| watts | ||
| ————— | ||
| power factor | watts | |
| current = | ——————— = | ————————— (3) |
| volts | power factor × volts |
Fig. 2,704.—Rope type of stranded copper cable which is used when a high degree of flexibility is required. The construction of this cable is the stranding together of seven groups, each containing seven wires and producing a total of 49 wires. In cases when a greater carrying capacity is desired than can be obtained through the use of the 7 × 7 or 49 wire cable, the number of groups is increased to nineteen thereby making a total of 133 wires (19 × 7).
EXAMPLE.—A 50 horse power 440 volt motor has a full load efficiency of .9 and power factor of .8. How much current is required?
Since the brake horse power of the motor is given, it is necessary to obtain the electrical horse power, thus
| brake horse power | 50 | |
| E.H.P. = | ———————— = | —— = 55.5 |
| efficiency | .9 |
which in watts is
55.5 × 746 = 41,403