Which statement describes the difference between two-wire and three-wire control circuits?

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Multiple Choice

Which statement describes the difference between two-wire and three-wire control circuits?

The main idea is where the control circuit’s power comes from. Two-wire control uses line power for the control circuit—the same supply that feeds the load drives the control coil or switch, so the control and load share the same source. Three-wire control uses an independent control power source, typically provided by a transformer, to energize the control circuit, so the control devices operate on a separate supply from the main line voltage. This separation makes control wiring more flexible and isolates the control circuitry from the main power. The other options don’t fit because they either misstate the power sources (phase, conductor count) or claim the power schemes are identical.

The main idea is where the control circuit’s power comes from. Two-wire control uses line power for the control circuit—the same supply that feeds the load drives the control coil or switch, so the control and load share the same source. Three-wire control uses an independent control power source, typically provided by a transformer, to energize the control circuit, so the control devices operate on a separate supply from the main line voltage. This separation makes control wiring more flexible and isolates the control circuitry from the main power. The other options don’t fit because they either misstate the power sources (phase, conductor count) or claim the power schemes are identical.

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