Which statement about voltage surges is consistent with the described coupling between phase and neutral?

• A. Phase voltage always increases
• B. Phase voltage decreases while neutral increases
• C. Phase voltage decreases and neutral decreases
• D. Phase voltage increases while neutral decreases

Answer: (B)

When a surge couples between phase and neutral, the energy doesn’t push both conductors in the same direction. Parasitic coupling paths and the relative impedances to ground set up a situation where current favors charging the neutral path more than the phase path. The neutral voltage rises as surge current returns through it, while the phase voltage tends to drop across the coupling impedance to keep the instantaneous current balance. So the observed effect is that the phase voltage decreases while the neutral voltage increases. This opposite movement is a natural consequence of the way energy is shared between closely coupled conductors during a transient.