Ground-Fault Circuit Interrupters

Ground-fault circuit interrupters (GFCIs) are a specialized type of circuit breaker designed to trip open whenever resistance between ground and the ungrounded conductor drops below 25,000 ohms. Any time current is diverted from the white wire, such as through your body when you grab a hot AC wire, the GFCI senses the absence of grounding current and opens the circuit, hopefully in time to prevent all your friends and relatives from having to make premature calls to the florist.

Just as with home installations, boats are required to have ground-fault circuit interrupter outlets on certain branch circuits of the AC service. This type of outlet is easily identified by the test and reset buttons located on the face plate. Many novice electricians assume that the purpose of GFCIs is to protect the circuit or device a circuit is feeding. Not so! GFCIs are intended to protect people from shock, not equipment.

GFCI protection is required in areas of the boat where excess moisture or a particular shock hazard may exist. Specifically, the ABYC recommends GFCIs in heads, galleys, engine rooms, and on deck. For all practical purposes, this means you may want a GFCI on every AC circuit on your boat.

In some cases, protection for all of these areas can be provided by just one GFCI outlet, with conventional outlets installed “downstream” from the GFCI. To protect the other outlets downstream, the GFCI must be the first outlet in the circuit. On larger boats, this protection may be broken up into more than one circuit, necessitating the use of several GFCI outlets.

Ignition Protection with GFCIs

All of this is of particular significance to boats that use gasoline as fuel and must meet ignition-protection requirements as discussed in chapter 4. Most GFCI outlets are not rated for ignition protection and therefore should never be used in engine rooms. Marine-grade GFCIs are available, but at considerable cost. This is really no problem for either the boatbuilder or you if you intend to add an outlet in your boat’s engine room. Simply use a conventional outlet in the space requiring ignition protection, and tie it into a GFCI outlet mounted in a safe area, such as in the galley. Figure 11-8illustrates how this arrangement should be wired.

Testing GFCI Outlets

All GFCI outlets used on boats must be tested monthly. The delicate internal mechanism of a GFCI outlet used in the harsh marine environment can corrode and cause the unit to not trip when you need it most. The simple test procedure is often overlooked, and not testing each outlet every month can cause obvious problems (it won’t work when it’s really needed).

TEST Green

White

RESET Black

GFCI OUTLET

STANDARD OUTLET

Fig. 11-8. A GFCI outlet with a non-GFCI outlet wired in to share protection.