Electrical, DC Main Circuit Breaker, Part 2: Wiring

The protective cover for the DC main circuit breaker

The wiring of a DC main circuit breaker would seem to be one of the easier tasks in the complete rewiring of a sailboat. After all, there are only two wires that join it. Things, though, in boat work, never are as easy as they seem. There are unexpected problems that create unexpected delays, and before you know it, what seemed at first as if it would require only a hour's worth of work ends up requiring much of the day. Replacing an existing component of an existing electrical system is not difficult. Creating an entirely new system is not. How much wire will I need? Where will I route it? Where will I terminate it? What size terminals do I need? Will this wire obstruct another that I will need to run through the same area tomorrow or the next day? How much chafe protection do I need? Is it the right size for the wire that I need to create for this component? For that matter, is the wire itself the right size for the job? Will it overheat? Have I taken into account the length of the run and the voltage drop? Wait a second, if I move up to a heavier gauge wire, then I'll need to order additional terminals, and maybe additional conduit, and maybe now the other wires that I planned to run through this area won't fit. These and many other similar questions I asked myself time and time again in the planning and execution of this complete rewiring of Oystercatcher my Ericson 25.

In this posting, the second of two in my article on the DC main circuit breaker, I describe the steps I took and the problems I solved to install two simple wires.

Let's start by looking at the protective cover for the DC breaker. You'll notice that there are two wires exiting it. The one on top is labeled "TO DC PANEL." The one on the right, that is fully sheathed, runs to the battery switch.

Now let's look on the other side of the bulkhead where things are nice and pretty. This was the way it looked after I had temporarily installed all of these components.The red switch is the battery switch. To right of it is the battery monitor, and to the right of the battery monitor is the DC breaker.

What I needed to do was to route a wire from the back of the battery switch (the red thing on the right) to the back of the DC breaker (the black thing on the left). It was clear from the start that I would have to route this wire around the back of the battery monitor (the round white thing in the middle). It was also clear that the blue protective cover that I had planned to install over the back of the battery monitor was no longer an option. It had to go.

What was not clear from the start, however, was that the thickness of the bulkhead would prevent me from connecting the wire from the battery switch to the back of the DC breaker.

Having made the wire and labeled it (tasks that I will not here describe, since I have described similar tasks in detail elsewhere in other articles) I now needed to figure out how to remove some of the plywood from the bulkhead in the area around the back of the DC breaker. You'll recall that I installed the DC breaker in the large hole where the old battery switch used to be. I was fortunate to have done this, because the extra space of this old hole gave me a little more working room.

Using my Dremel, with a sanding drum attached, I slowly routed out pathways of sorts for the two wires, being very cautious not to nick any of the wires in the vicinity. This tool can do a lot of damage in short period of time, if you're not careful. I should note that I did all of this work on my knees, while leaning into the cockpit locker.

I also had to be cautious about sanding too deeply. Otherwise, I would create not a rut, but a hole - a hole clean through the bulkhead. Note that I have covered the back of the battery monitor with duct tape to prevent dust from damaging the instrument.

Once I had routed out these pathways to a sufficient depth, I temporarily installed the two wires on the back of the DC breaker. I continue to use the word wire, but since this wire is 6 AWG (American Wire Gauge), it is normally classified as a cable.

At any rate, the wire that I routed upward from the back of the DC breaker led to the DC distribution panels in the galley. To get there, I routed the wire up and over the blue protective cover for the back of the bilge pump switches. Then I routed it through a small opening between the bulkhead and the hull. This wire, sheathed in a black, split-loom conduit, is near the gray plastic conduit on the far left. You just can't see it in this picture. Note that I used the white AC three-wire cable to hold the wire in place.

Below is a picture of the galley. To the left you can see the various white labeled conduits that I have routed through the small opening between the bulkhead and the hull. To right you can see a Blue Sea Systems terminal stud. It was to this stud that I would connect the wire from the DC breaker. The gray, blue, and orange wires are for the DC branch circuits. I address these in separate articles.

Here's the terminal stud after I have connected the 6 AWG wire to it. The other wires, which are 10 AWG, feed the three DC distribution panels. Connecting these three wires to the panels was one of the last things that I did in this complete rewiring of the boat. By this point, the only 10 AWG wire that I had left was yellow, the color I used elsewhere to indicate negative. Not wanting to order another spool of 10 AWG for such a small amount of wire, I decided to use the yellow 10 AWG but to color-code it with red tape and to label it with a + sign to make it clear that it was positive.

Before going any further I needed to seal the joint between the bulkhead and the hull liner in the galley. To do this, I used NP1, a polyurethane adhesive/sealant not unlike 3M 4200 or Sikaflex. NP1 is available in good hardware stores and, since it's sold as a construction material and not a "marine" material, it's much less expensive. It comes in a variety of colors. I selected Off White to match the interior of the boat.

There was a small gap in the joint. I wanted to seal this, so that air would not freely move between the interior of the boat and the cockpit. The NP1 worked well, and the Off White color blended perfectly with the color of the gelcoat on the interior of the boat.

The next issue I faced concerned the final installation of the breaker itself. Up until this point the breaker was only loosely seated in its housing with short screws. Now I needed to mount it with fasteners of sufficient length to prevent it from working itself free. I did not have fasteners of sufficient length, so I had to make a trip to the hardware store. Fortunately, here in Charleston, South Carolina, there are still some traditional hardware stores that sell individual stainless steel fasteners from open bins rather than prepackaged fasteners in quantities that you often do not need.

The fasteners had to be long enough to penetrate the first or second layer of the bulkhead, but not too long that they would pass all the way through these layers.

The DC breaker as it appeared shortly after I had screwed it fully into position.

One problem that I ran into, in terms of the fasteners was that, in the area above the back of the breaker, there was no bulkhead into which I could screw a fastener. The only material that the fastener could grab was the mahogany of the decorative backer. This was not necessarily a problem in and of itself. The problem, rather, was that the end of the fastener penetrated the mahogany and projected into the space where the wire for the DC panel needed to run. To remedy this problem, I pulled out the Dremel and sanded away the end of the fastener. By the time I finished, all that was left was a small stainless steel nub that was barely detectable when touched by a fingertip.

Despite the smoothness and the almost non-existence of this nub, I still thought it would be wise to cover it with several layers of black electrical tape. This was insurance of sorts against the possibility of chafing action.

Next, I needed to focus more closely on the wire that ran from the battery switch to the breaker. Up until this point it was just loosely connected to these two components.

One reason I kept it loose was because I still needed to connect the 1 AWG wires to the back of the battery switch. I had to be sure that this 6 AWG wire would fit with all of these larger wires in this space.

Fortunately, it looked like it would, so I screwed the protective cover into place over the back of the battery switch.

Now I was able to focus on tightening the nuts on the back of the DC breaker and finding a protective cover for it.

Here I encountered another obstacle. When I had earlier hand tightened the lock nuts on these studs on the back of the breaker, everything seemed okay. Now, using a ratchet wrench, I could not get a good grip on these nuts. Therefore, I experimented with different nuts in my miscellaneous bag of stainless steel hardware. A number 10 nut was too small, and a 1/4 inch nut was too large. Puzzled, I made a trip to the hardware store. There, I discovered that the nut I needed was in fact a metric sized nut. Fortunately, this hardware store keeps stainless steel metric fasteners in stock. Back at the boat, I tightened these metric nuts into place using a metric ratchet - a tool that I rarely use, but one that I am glad that I had. I'm still not sure why Blue Sea Systems opted for the metric system on this breaker when they use the English system on all their other components that I have encountered. While I'm at it, I should note that I was able to solve this metric puzzle by taking the original nuts to the hardware store. Yes, this breaker came with nuts. I needed a second set of nuts, because I used the first set as stand-offs. In other words, I installed them behind the lugs. This helped me in the seating of these lugs in this tight space.

Now that I had solved the nut problem, I needed to solve another. As I contemplated how I might protect the back of the DC breaker, I slowly began to remember a conversation that I had had with the tech person at Blue Sea Systems and the notes I had taken at that time. I had asked this tech person if I needed to fuse the wire that would run between the battery switch and the DC breaker. He said that, according to ABYC (American Boat and Yacht Council) standards, the battery switch is a power source. Therefore, he said, if the wire coming off it were to be over 7 inches in length, then it would need to be protected by a fuse. He added, however, that if this wire were to be protected by a sheath or conduit, then it could be up to 40 inches in length without being protected by a fuse. After consulting my notes, I pulled out my tape measure to check the length of the wire. Sure enough, it was an inch or two over the 7 inch limit. I knew that given the space restrictions a fuse was out of the question. Therefore, I decided on the quickest and easiest solution possible - sheathing the wire in a split-loom conduit.

This was something that I really should have done in the first place, given the twists and turns that this wire had to make in such a small space, and given the proximity of this wire to the wire that fed the DC distribution panels. As an added measure of protection I wrapped the end of the conduit many times with black electrical tape to insulate this wire from the adjacent one on the back of the breaker.

In terms of protecting the back of the breaker itself, I experimented with several options until I settled on the one you see pictured below. Yes, this is an electrical box for an AC receptacle. Specifically, it is known as a "shallow work" box, due to its slim profile. It fit perfectly in this space, and it left plenty of room for the two wires to enter and exit the box.

At this point, my complete rewiring of the boat was almost at its end. This is the way the cockpit locker appeared at this time.

Despite the fact that it was obvious to me at this moment that this was the main DC breaker, I still went ahead and labeled the box. This would provide immediate recognition and clarity for me or for anyone else (who might be assisting me) at any point in the future.

Yes, this was a lot of work for two simple wires, but then again I could tell countless stories of similar tasks in the refitting of this boat that seemed at first to be simple, but ended up being much more time consuming than I had ever imagined.

This ends this posting on how I wired the DC main circuit breaker on Oystercatcher, my Ericson 25.