A. Master electrician Rex Cauldwell responds: Some equipment, including some spas, are pure 240-volt, with no neutral. Most everything else is both 120- and 240-volt. It doesn't make any difference if the load is pure 240-volt (with two hots and no neutral) or 120/240-volt (with two hots and a neutral) — you use the same double-pole GFCI breaker. You even install it the same. Wire both hot conductors to the breaker and the breaker pigtail to the neutral bus. There will be no connection to the breaker neutral, so just ignore it.
The way the breaker works is via "vector addition." It sums the current of the load and uses that as a reference as the current leaves one leg of the breaker. In theory, the current coming back should be the same. If it is not, the breaker opens. The vector addition will not work if the pigtail is not connected.
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