Power cords, amplifying
OK, imagine four objects: you, your boat, the shore power box, and the shore power cord. The shore power cord has two distinguished ends: boat plug and shore plug. This system has four relevant states, depending on which ends of the cord are attached. UNPLUGGED (UNENERGIZED, SAFE): Neither end of the power cord is connected. If you fall in the water with it coiled around your shoulder, it is a weight that may entangle you, but it won't electrocuted you. FULLY PLUGGED (LIVE, SAFE): The power cord is plugged in at both boat and shore. Electricity courses through it, but even if the middle of the cord falls in the water, its heavy insulation prevents any shock to swimmers. BOAT-PLUGGED (UNENERGIZED, SAFE): The power cord is plugged in at the boat, and the shore end is free. Your boat's electrical system does NOT energize the power cord. If you fall into the drink with the unplugged end, the cord may entangle you, but it won't electrocute you. SHORE-PLUGGED (LIVE, DEADLY): The power cord is plugged in at the shore, and the boat end is free. The power cord is energized with 120VAC or 240VAC. If you trip and fall in the drink with the free end, you will be severely shocked before you drown. Safety rule: NEVER let a power cord get in the last state. Instead, always pass through the "boat plugged" state. If you are removing shore power, unplug it at the SHORE before the boat. If you are plugging in, always plug in the BOAT before the shore. In other words, the dangerous shore connection should be made last and undone first.And, yes, I know. There is also a switch on the shore box, and if it is fully switched off, the cord is unenergized. And, yes, there is some likelihood, in the worst case, that the shore's circuit breaker will flip before you are completely disabled in the water. The funny thing is: with all these automatic safety checks, people still die from mixing AC and water.