Re: Shore Power Voltage Drop
Voltage drop accumulates all along the path from the utility's transformer up to the point of utilization, proportional to resistance in the circuit. It includes the marina's service equipment and distribution system, your extension cord and your boat's circuitry. It only becomes evident as more current is used.
The variations in voltage that you're seeing may be coincident with changes to the load on the system caused by other boaters. I expect that the available voltage will be at its lowest when the marina is well occupied and perhaps on a hot day when a number of air conditioners are running. If that is the case, the voltage will read low even before you add your 10 amp load. If the addition of your 10 amps causes the voltage to drop dramatically from normal levels, then the problem is likely local to your boat. It could be that the marina's wire size to your slip is too small or too long or both. To ensure that your equipment doesn't contribute the last straw that increases the accumulated voltage drop to an unacceptable point, I suggest you use the shortest extension cord possible with the largest gauge of wire that you can afford to buy.
As mentioned by others, loose connections can cause this problem too, but unless there's an obvious hot spot, my bet would be that the wire size in the distribution system is inadequate. - Grandad
