Stray Current Protection
When shore power develops a “leak” on board and stray current is present, it will find all possible ways to return to its source. That source is, of course, shore-based, and ground is the boatyard or marina, so current will flow through the water as part of its path home. This can upset devices aboard other vessels and be potentially lethal to a swimmer.
For many years on-board ground-fault circuit interrupters, usually as part of a receptacle, kept people safe from stray current. Just like at home, the boat had them in areas where shock hazards are present, and American Boat & Yacht Council standards mandated them in the galley, head, engine room and exposed weather decks.
It was then decided that whole-boat protection, similar to the European standard, provides a safer environment in and around a boat using shore power. Because of the nature of typical stray-current sources, the new device is called an equipment leakage circuit interrupter and is also a residual current device.
An ELCI circuit breaker measures the electrical current flowing in the two conductors carrying current — black (ungrounded, or “hot”) and white (grounded, or “neutral”) — to the vessel’s loads and back, and compares them. If there is leakage with a device, the current flowing to it will be greater than the current returning. If the difference exceeds 30mA (0.030 of an amp), the whole shore power circuit is broken.
The ELCI circuit breaker also will open when total current exceeds the 30-amp threshold, so it is the first device through which shore power flows. It can be located in one of two places, determined by the length of the shore power conductor in the boat from the inlet to the main panel. If the conductor length is less than 10 feet, the ELCI can be at the panel. If the distance along the wire is greater than 10 feet, the ELCI must be adjacent to the inlet as the first device in line.
The ELCI is an important safety device. If a new system is being installed, include an ELCI in the circuit.