|Test fitting the freshly cut panel frame.|
|Shore power AC panel and meter showing AC current.|
|Panel hinges down for easy access.|
|Finished install. Meter is showing AC voltage.|
|A motivating goal: removal of the rat's nest of extension cords.|
Readers have probably heard of GFCI outlets. GFCI stands for "Ground Fault Circuit Interrupter". One commonly sees these sorts of outlets in house bathrooms and lavatories (squarish looking outlets, with red and black buttons, sometimes). GFCI outlets provide fire hazard safety such that they can detect an "electrical short" to ground (green wire) and automatically switch off the circuit in such an event.
ELCI, stands for "Electrical Leakage Circuit Interrupter", and goes one better than GFCI. These switches, installed between the shore power connection and AC distribution panel, monitor current flow on the HOT (black) and NEUTRAL (white) lines of an AC circuit. Physics asserts that the sum current of both sides must be equal to zero at any given time (current in, must equal current out). Any electrical leak will create an imbalance (non-zero sum) detected by the ELCI cutting off the circuit (within a 30 milli-amp tolerance, typically). A short to the ground wire (green) creates such an imbalance and qualifies as an electrical leak, thus ELCI provides the same protection as GFCI.
ELCI switches are more expensive than GFCI switches. So, why not just use a GFCI? Well, when the boat is connected to shore power, protection by a GFCI is only as good as the wiring of the dock's shore power system. All marina shore power wiring can vary in quality (despite local codes). If the ground of the dockside shore power socket has poor or no earth ground, a GFCI will provide NO protection AT ALL.
On a boat, there are more potential paths to earth ground than the shore power's green wire. The boat's bonding system, to metal thru-hulls, to seawater is a common point of electrical leakage faults. Such faults can cause lots of problems not only for your boat's underwater metals (thru hulls and zinc anodes), but those of neighboring boats as well. And any diver, changing zincs underwater, in the vicinity of such a fault, may not be having a great time either.
An ELCI installed on the boat, between the shorepower connection and AC distribution will protect against these faults. Shore power connection ELCIs are now required as part of the ABYC E-11 specification. If you have a steel or aluminum boat, an ELCI is an absolute MUST in my opinion.