In addition to the forces involved the heating effect of large cur-
rents must be considered.
Power loss = PR watts.
Increasing the circuit current from 20 A to 2500 A will increase the
power loss by a factor (2500/20)
or 15 625 times. It is easy to envis-
age the effect this will have on the circuit insulation. Within a few
cycles of an a.c. supply, plastic insulation will melt.
HEATING OF CABLES Since all conductors in normal service have resistance, the passage
of current along the conductor gives rise to a voltage drop. The