Circuit, Interrupted


When was the last time you checked your onboard ground fault circuit interrupters (GFCIs)? Recent data indicate that approximately 30 percent of GFCI outlets installed in homes and 50 percent of the units in the marine environment don’t work, mostly because they are sensitive electronic instruments that are easily damaged by spikes in power or the environment where they reside. These devices have an extremely high failure rate, especially in the marine environment. One of the reasons for failure is that few of us follow the Underwriters Laboratories standards and the manufacturer’s “test monthly” suggestion. Doing so helps exercise the mechanism inside the unit, ensuring it can move freely when called into action.

A GFCI outlet adds a greater level of safety by reducing the risk of electric shock. The American Boat and Yacht Council (ABYC) recommends the use of ground fault protection receptacles in a head, galley and machinery space or on a weather deck (splash or spray). The units are designed to protect people from line-to-ground electrical shock hazards by monitoring for a current imbalance between the hot and neutral wire, and they break the circuit if that condition occurs. A circuit breaker usually will trip if you receive a shock, but it may not act fast enough to protect you from harm. A GFCI outlet is more sensitive and acts faster than a circuit breaker or fuse and, thus, is an important safety feature. A GFCI is different than a circuit breaker in that the GFCI is designed to protect you, and a circuit breaker is there to protect the electrical conductors.

In a properly wired GFCI, the slightly larger left slot is called “neutral” (white conductor), the right slot is called “hot” (black conductor) and the hole below them is called “ground” (green conductor). If an appliance is working properly, all electricity the appliance uses will flow from hot to neutral, and a GFCI monitors that amount of current. Basic electrical theory says that whatever voltage goes in must equal what is going out. If there is any imbalance (fault), then that difference is going somewhere it was not intended. If a fault does occur and the leakage level exceeds four to six milliamps, the GFCI unit can react as quickly as one-30th of a second to protect the user by opening the circuit, thus interrupting the power supply and limiting the duration of any electrical current flow. This quick action is too little time for current to build to a dangerous level.

A GFCI outlet may be wired in a branch circuit, which means other outlets and electrical devices may share the same circuit and breaker. When a properly wired GFCI trips, the other devices down the line from it will also lose power.

GFCI outlets should be tested periodically, at least once a month, using the “Test” and “Reset” buttons, which need exercise, because it takes very little corrosion to render them useless. Pressing the “Test” button will trip the outlet and break the circuit. Pressing “Reset” will restore the circuit. Some units have a small indicator light to show that they have power. If you press the “Test” button but the outlet still has power, the outlet is miswired. A miswired outlet is dangerous and should be fixed immediately.

GFCIs are inexpensive and easy to replace. Use only high-quality devices from a reliable manufacturer and not the cheap ones from the local discount store, and test one immediately after replacing it.

In 2015, Underwriters Laboratories published a new standard applying to all permanently installed GFCIs. UL 943 requires all units to automatically monitor GFCI functionality every three hours or less. If the device can no longer provide this protection, it must deny power and provide a visual and/or audible indication for end of life.


Read an update to this article written by a Sea Magazine reader.

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