What type of current does a GFCI protect against?

A Ground Fault Circuit Interrupter (GFCI) is designed specifically to protect against ground faults, which occur when there is an unintended path between an electrical source and a grounded surface, usually due to the presence of moisture or faulty wiring. A GFCI monitors the current flowing in a circuit and compares the current going to the load with the current returning. If there is a discrepancy, indicating that some of the current is leaking to the ground, the GFCI will quickly cut off the power to prevent electric shock.

This protection is critical in areas where electrical outlets may come into contact with water, such as kitchens, bathrooms, and outdoor spaces. The GFCI significantly enhances safety by reducing the risk of electrical shock or electrocution in those environments.

While direct current and alternating current are types of electrical current, GFCI devices aren't designed specifically to provide protection against them; instead, they focus on detecting ground faults. Surge current pertains to brief spikes in voltage, which could be caused by lightning strikes or power surges, but again, GFCIs do not provide protection against such events. Thus, the primary function and protective capability of a GFCI revolves around ground faults, making it the correct answer.