RCD/ELCI's are a very good idea however at this point I don't know of anyone who has the 3106 in stock as I was looking for one last month. Also keep in mind that this breaker takes up three slots on your panel as opposed to two so some re-routing will be necessary if updating an existing panel that uses "world series" circuit breakers.
Here's some more background that I posted last year on SN :
Some confusion lies with the new ABYC E-11 requirements.
The update to E-11 requires an RCD (Residual Current Device) or ELCI (Equipment Leakage Circuit Interrupter). This requirement however is brand new and was only mandated for ABYC compliant builders as of 7/31/2010. It was supposed to go into effect back in 2009 but the market could not supply the product fast enough.
11.4.10 Equipment Leakage Circuit Interrupter (ELCI) - A residual current device which detects equipment ground fault leakage current and disconnects all ungrounded (110 V & 240V) and grounded (110 V neutral) current carrying conductors from the supply source at a preset trip threshold.
A regular GFCI interrupts current at a 5mA level and an ELCI at a 30 mA level. In an AC system that is working as it should the amount of current flowing through the neutral and hot wires is supposed to be equal. If it is not this denotes "leakage" or a ground fault. This leakage is often due to wire jacketing that has been breached but can also happen internally in inverters or battery chargers due to corrosion or failure etc. etc..
If the hot AC wire is leaking and you also have a faulty AC green ground wire, happens a LOT more than you'd think, then the AC current tries to find it's way to ground and can energize just about anything it can leading to dangerous shock hazards both on-board and in the water near the vessel.
An ELCI or GFCI monitors the balance of electricity in the wires and if it sees a 5 mA (GFCI) or 30 mA (ELCI) difference or imbalance it opens and breaks the circuit.
ELCI's protect the entire vessel and should be within 10' of the shore power inlet. Keep in mind this is 10 feet of wire not as the crow flies. If your shore power inlet is within 10 feet of wire then the ELCI can serve as your main AC breaker.
The Blue Seas 3106 toggle ELCI is intended to retrofit and replaces the standard world series double pole breaker. It is an easy retrofit and but it does take up an additional slot in the panel over the double pole breaker, three slots vs. two.
GFCI's protect individual AC branch circuits at 5 mA. GFCI's should be used in the galley, head, machinery spaces or in a weather deck location.
A properly wired double pole breaker within 10' WIRE feet from the shore power inlet is still okay for the existing boat owner provided it is wired correctly and your AC ground (green wire) is connected to the DC ground buss on the boat and also back to shore.
ELCI's are a great idea and eventually the price will come down. I suspect a lot of retrofit applications will uncover some leakage that was previously unknown and this will be a good thing!
