Cruising in the south sound last August, we arrived at the Poulsbo Marina. Calling in on channel 66A we were assigned our slip along “D” dock. We went through the usual litany of our arrival check list. All went well and after tying up we plugged in to the 30 Amp shore power service and were about to head for the harbor master’s office to check in, when we noticed our monitor indicated we were not getting power. After double checking we mentioned this to the office manager. She happened to have an electrician right there and he was sent down to our boat.
“Your boat has a problem”, he told us. As it turned out several other boats just arriving were suffering from the same issue. He explained that as marinas and docks upgrade their facilities, they will be adding Ground-Fault Interrupt (GFI) protection breakers to shore power receptacles. GFI breakers are designed to trip and turn-off power if it detects an imbalance in the power (amperage) going to the boat and returning via the shore power cable/wiring. In the past, marina shore power receptacle breakers have only had over-amperage breaker switches to protect the shore power wires and cables. These new GFI breakers will trip, turning off power, if the boat incorrectly leaks amperage, and will trip if too much amperage is consumed.
Upon returning to our home port I contacted my electrician and after explaining what had happened he suggested I might need what is called an Isolation Transformer. After a bit on on-line research I began to understand the situation better. Apparently, my boat along with a lot of older boats, give off stray voltage into the water and back to the shore power box.
Solution: Either spend what could be quit a lot of money searching for the source of the stray voltage aboard or, install the Isolation Transformer. My electrician advised the later for my particular situation.
So, on a recent morning, Shawn from Pacific Marine Electric showed up with his tools and a heavy wooden crate. The crate contained a heavy metal case containing two copper coils buried in a mixture of sand and epoxy and the connectors for the wiring to the boat. Shawn opened up both the forward hatch leading to the utility tunnel in the deck just below the main helm and the AC breaker panel. In about 3 hours he had the unit installed.
My unit, a Charles Marine ISO-G2 3.6 kVA Isolation Transformer weighs in at 70 pounds and costs around $650 shipped. It must be wired within 10 feet of the shore power inlet on the boat. Wired up, it quietly (does have a faint hum) and completely isolates input power from output power for improved safety and prevents galvanic current corrosion due to direct connection to AC shore power. Basically, it isolates the boat eliminating our problem. We should also see an improvement in the longevity of our zincs. In short, we are now prepared for the coming modernization of our marinas both here and in Canada.
Shawn also noticed the plug in for shore power on the boat and the shore power cord were corroded and recommended they be replaced I had him relace the boat plug immediately and ordered a new Marinco 30 amp cord. Aside from corrosion control measures at connestion points around the boat, I can't imagine what else we can do to make our boat as up to date as possible electrically.