The Offshore Voyaging Reference Site

Why I Won’t Power Our Boat With a Portable Generator

A few weeks ago we published an article on the dangerous issues I have found in the shore power system on our new-to-us J/109 and what I’m doing to fix them.

During the ensuing discussion a member asked whether or not supplying power to a cruising boat with a portable generator through the shore power cable was safe.

I have to confess that I had never really thought about it, and that Phyllis and I did just that while taking care of a friend’s boat one winter in Greenland.

And while I’m in the confessional I also have to admit that I was considering just that option (among several others) for our J/109.

But when I started really thinking about this, I was surprised how difficult I found it to quantify the dangers and understand the solutions (if any), despite having a good understanding of electricity from my time as a mainframe computer technician back in the day when the machines filled rooms.

The big issue here is where the neutral and ground wires are tied together as well as the earth itself. Getting this right is a fundamental requirement for shore power safety.

So first off let’s take a look at how things work when we are plugged into a marina shore power system, and then we will see how plugging into a generator is different.

Note: Everything that follows is applicable to North America only. There may be differences in other countries, but as we will see, I don’t need to get into that to reach my conclusion.