What happens to the magnetic or mechanical stress when the peak current is reduced to one third during a short-circuit condition?

When the peak current during a short-circuit condition is reduced to one third, the mechanical and magnetic stresses associated with that current also change significantly. In electrical systems, the stress is often proportional to the square of the current. Therefore, if the current is reduced to one third, you would calculate the new stress as follows:

1. The original stress at peak current can be represented as proportional to ( I^2 ), where ( I ) is the current.

2. If the current is reduced to ( \frac{1}{3} I ), then the new stress is calculated as ( \left(\frac{1}{3} I\right)^2 = \frac{1}{9} I^2 ).

3. In this case, the new stress is one ninth of the original stress.

This relationship demonstrates why the correct answer indicates that the stress is cut to one ninth when the peak current is reduced to one third. Understanding this quadratic relationship between current and stress is crucial for evaluating short-circuit scenarios and ensuring safety in electrical designs.