When paralleling the outputs of two generators, how close must the output voltages be?

When paralleling the outputs of two generators, how close must the output voltages be?

• A. Within a few tenths of a volt.
• B. Within 1 volt.
• C. Within 5 volts.
• D. Exactly equal.

Answer: (A)

When you parallel two generators, their voltages have to line up very closely to prevent currents from flowing between them and to ensure the load is shared predictably. The best practical target is to bring their outputs to within a few tenths of a volt of each other. That tight tolerance keeps circulating currents very small, reduces stress on the generators and bus, and helps the regulators share load smoothly. If the voltage difference is larger, even a small mismatch on a typical 120-volt system can create noticeable circulating current, which can cause overheating, tripping of protective devices, or uneven load sharing. Saying within 1 volt is looser and could still produce unnecessary circulating current, while within 5 volts is far too large for safe, stable paralleling. Exact equality isn’t achievable due to regulator tolerances and dynamic response, so the practical standard is a small difference—on the order of a few tenths of a volt.

When you parallel two generators, their voltages have to line up very closely to prevent currents from flowing between them and to ensure the load is shared predictably. The best practical target is to bring their outputs to within a few tenths of a volt of each other. That tight tolerance keeps circulating currents very small, reduces stress on the generators and bus, and helps the regulators share load smoothly.

If the voltage difference is larger, even a small mismatch on a typical 120-volt system can create noticeable circulating current, which can cause overheating, tripping of protective devices, or uneven load sharing. Saying within 1 volt is looser and could still produce unnecessary circulating current, while within 5 volts is far too large for safe, stable paralleling. Exact equality isn’t achievable due to regulator tolerances and dynamic response, so the practical standard is a small difference—on the order of a few tenths of a volt.