When a capacitor bank is open and the neutral bus is floated, what voltage will appear on the ungrounded neutral bus?

When a capacitor bank is open and the neutral bus is floated, the voltage that appears on the ungrounded neutral bus is one-half of the phase to ground voltage.

This phenomenon occurs due to the behavior of capacitors in a three-phase system. When the neutral is not grounded, and the capacitor bank is isolated, the influence of the electrical fields associated with the energized phase conductors causes the neutral bus to float at a potential that is influenced by these voltages. Specifically, in a balanced load condition, the neutral point will have a voltage that is equal to half of the voltage measured from phase to ground, reflecting the symmetrical distribution of the phase-to-phase voltages.

In more technical terms, if the system is symmetrical and balanced, the vector sum of the phase voltages leads to this specific relationship at the neutral point. Thus, the floating neutral does not sit at ground potential; instead, it maintains a voltage that is inherently defined by the characteristics of the three-phase system.

This outcome is critical for understanding how to manage and operate capacitor banks safely and effectively in a power distribution system, especially during maintenance or fault conditions.