Electrical, DC Main Circuit Breaker, Part I: Analysis and Installation

The DC main circuit breaker on Oystercatcher
DC electrical systems, based on one or more battery banks, are the work horses of cruising sailboats. Many important parts of the boat are normally powered by direct current - the navigation lights, the steaming light, and the anchor light, just to name a few. Oh, and let's not neglect to mention the GPS, the VHF radio, and the lights on the interior of the boat. The positive cables from the battery banks are led to the battery switch. From the Common post on the battery switch, a single cable is lead to the DC main circuit breaker. From the DC breaker a single cable is lead to the DC distribution panel, or panels. The DC breaker thus serves as a gatekeeper of sorts for the DC electrical system. Any excessive surge of direct current (DC) from one or both of the battery banks will cause the breaker to trip, thus preventing the surge from entering the smaller, less hearty wires of the DC electrical system downstream. To the electrically well-read and well-practiced, these words might be excessively simple, but to the majority who aren't, perhaps they are helpful. Putting these words down at least helps me be more sharp-minded in my understanding of the electrical system, that system that is, without a doubt, the most difficult to grasp firmly and confidently in the refitting of a sailboat. In this two-part article I will not belabor the purpose or the virtues of a DC main circuit breaker any further. I will instead simply describe my reasons for selecting the location that I selected for the breaker, and I will describe how I installed it and wired it on Oystercatcher, my Ericson 25.
Blue Sea Systems brand 285 series, 70 amp, breaker, PN 7085
The original DC electrical system on my boat, at the time of purchase in 2009, was not just corroded, but also was outdated, undersized, and plagued with all sorts of ill-conceived and unsafe modifications. I have addressed many of these problems in my article, "Electrical, Original."
The original DC distribution panels and battery switches on all Ericson 25s, that I have seen, were placed by the manufacturer on the bulkhead adjacent to the stove. I have discussed the sound reasoning behind this choice for the location for these items in my article, "Electrical, AC Distribution Panel." Here, I will only add one thing - that Ericson neglected to consider (or at least include), back in mid-1970s, a DC main circuit breaker between the battery switch and the distribution panel. Why? I don't know. Maybe that was the norm.
If you've read that AC distribution panel article I mentioned above, then you'll know that I used cardboard mock-ups to help me figure out whether or not I could fit everything I needed to fit into this space - the AC panel, the bilge pump switches, the battery switch, the battery monitor, and the DC main circuit breaker.
You'll also know that my plan was to create trim pieces for all of the components, in order to make them blend harmoniously with the existing mahogany trim that was original to the boat.
I used sapele mahogany for this project, the same type of wood that I had used for many other projects on this boat. See my article, "Companionway Hatch Construction," if your interested in learning more about this wood.
The trim pieces fit quite nicely when I loosely put them into place.
One of the hallmarks of mahogany, especially when quarter-sawn, is what is known as the ribbon-stripe pattern. If you're an Ericson 25 owner, check out your bulkheads in the main salon and V-berth. There are vertically oriented ribbon-stripes all over them.
I first installed the AC distribution panel, then the bilge pump switches, and then the battery switch.
The Blue Sea Systems brand 285 series panel mount breaker requires its own Blue Sea Systems brand trim piece. There are two choices, the panel mount adaptor (PN 7198) or the bezel mount adaptor (PN 7098). The former allows for flush-mounting. The latter, as you can see in the picture below, cause the breaker to protrude about 3/4 inch from the mounting surface. I liked the idea of flush-mounting the breaker, but I did not like the idea of having to cut a square shaped hole through the bulkhead. There is very little room for error in the cutting of this square hole, since the panel mount adaptor (PN 7198) is not a large trim-piece, i.e., one that would disguise a mistake. The benefit of choosing the bezel mount adaptor (PN 7098), is that it allows you to mount the breaker in a round hole - a hole that you can cut relatively easily with a hole saw. The bezel mount adaptor is designed to disguise the edges of this hole.
Below you see the back of the mahogany trim piece and the circular hole that I cut with the hole saw.
In the picture below, ignore the hole on the left. That one I had earlier cut for the battery monitor. Focus instead on the one on the right. I didn't have to cut a hole through the bulkhead for that one, since there was already a large hole in that spot for the old battery switch. In terms of the mahogany trim piece itself, I had no choice but to mount the DC breaker in this position. The bezel mount adaptor, as I said, causes the DC breaker to protrude from the mounting surface by about 3/4 inch. The stovetop on the Origo stove swings upward on a hinge along its backside. The purpose of this hinged stovetop is to allow the user to extract the two alcohol fuel canisters within the stove for the purpose of refilling them with fuel. If I had installed the DC breaker in the middle position, I would not have been able to open the stovetop. Even in the position nearest to the AC panel, the DC breaker still impeded the opening of the stovetop somewhat, but not enough to prevent the removal of the canisters.
The bezel mount adaptor installed.
The breaker installed within the bezel mount adaptor.
Below we see the inside of the cockpit locker with the backside of the AC panel, the two bilge switches, and the DC breaker protruding through the bulkhead. This allows you to see more clearly what I was talking about, when I said that I mounted the DC breaker in the hole that had originally been dedicated to the defunct battery switch.
All in all, I thought the installation of these various components was looking pretty good at this point.
This ends this posting on my installation of the DC main circuit breaker on Oystercatcher, my Ericson 25.

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