When testing a GFCI outlet that is not grounded, how will the outlet respond?

When testing a GFCI outlet that is not grounded, the expected behavior is that it will trip when using the test button on the outlet itself. This action simulates a ground fault condition which is the primary purpose of the GFCI. The device is designed to detect an imbalance in the electrical current flowing through its circuitry, and it will shut off power to prevent electric shock.

However, when using a tester on an ungrounded GFCI outlet, it may not register properly, often because the tester relies on a ground reference to function correctly. As a result, the GFCI will not trip in response to the tester if it does not detect a fault condition that is consistent with its intended function. Thus, the outlet will successfully trip during a test with its built-in button, indicating that it is operational and can provide protection against ground faults. This behavior confirms the integrity of the GFCI mechanism, even in the absence of a ground connection.