Here is a photo of the marine battery installation on my new French-built catamaran. There are things going on here that I’ve never seen before. My main concern is the flat copper bars the builder used to connect my batteries. Shouldn’t this be done with copper cables, as I have always seen it done in the past?

marine battery installation

Yellow arrows point to areas of concern in this battery installation.


Good question. The short answer is yes, cable is recommended. The big question here is the actual area involved. Wire and cable use a circular mil area formula to determine the conductor’s capacity to handle X amount of electrical current (amperage). There is an alternative square mil area formula for the purpose of determining the amperage handling characteristics of things like terminal bus bars and the like.

The risk here has to do with the flexural characteristics of copper bar vs. cable. Cable is recommended to accommodate the natural movement and flexing that is expected on a boat. That said, the links you show in your photo appear fairly short and not too likely to need to do much flexing, so things will probably work out okay on that front. Also, the actual bars are covered with insulating material, which is a good thing for safety. As for the actual conductivity level of the bars vs. short cable pieces, as long as they are not heating up when the system is in use then they have enough amperage handling capability for the task at hand.

What does concern me, looking at the photo, is that the positive terminal and negative terminals (see yellow arrows) do not have insulating covers on them. This could be dangerous if the terminals had a metal object fall on them while underway. It is certainly not standards compliant.

Finally, the arrows we added to your photo are also pointing at the fuses that are connected directly to several of the battery posts. These are probably for some accessories that were added to the boat after the fact. The question becomes whether or not these fuse holders are in fact rated for ignition protection. I do not believe they are. So, if the batteries were on charge and there was any gassing going on in the batteries that got released in the area and a fuse blew, an explosion could occur. Keep in mind that even sealed batteries have vents that only open when excess pressure builds up inside the battery case in the event of overcharging. So, expulsion of explosive hydrogen gas is still something to consider.

See other key questions answered by Ed Sherman, like Is my compass accurate? and Is my boarding ladder safe?

Written by: Ed Sherman
Ed Sherman is a regular contributor to, as well as to Professional Boatbuilder and Cruising World, where he previously was electronics editor. He also is the curriculum director for the American Boat and Yacht Council. Previously, Ed was chairman of the Marine Technology Department at the New England Institute of Technology. Ed’s blog posts appear courtesy of his website, EdsBoatTips.