Replacing The Boats Main Electrical Panel

One of the major projects on my to-do list is finally finished. The original 30-year-old main electrical panel is now a thing of the past, and several of the upgrades I have been wanting to do are finally finished. Before I even begin, let me add a strong word of caution here. If you are, in any way, unfamiliar with the electrical systems on a boat or unsure of your capabilities, don't try and tackle this yourself. I have been doing this for a living for many years, so I have already made all of the mistakes, and a misstep in working with either the DC side or the AC side of a boats electrical systems can have devastating affects for not only yourself, but every other boat nearby.

A terrible marina fire at McCotter's Marina, Washington, NC has been traced to an electrical issue on board one of the boats in a covered slip. Doing any electrical repairs or upgrades to your boat can have disastrous consequences if not properly done. These kinds of projects should not be taken lightly considering the potential for disaster. Having said that, the replacement went rather well with few surprises, after all this is a boat.

Rather than try and list all of the proper tools, I consider a picture worth at least a thousand words. If you plan on doing any electrical work on the boat for repairs, upgrades or additions, I highly recommend that you spend a few extra dollars and get the proper tools and not cut corners. Your average inexpensive hardware store crimpers and strippers may not be the best choice. At a minimum, I like to use a pair of strippers that allow me to be specific with the wire size and will not damage the wire itself while removing the outer covering. Most of the wiring problems I have encountered comes from two issues. One is corrosion which is a constant battle on a boat, and the other is from faulty connectors. Faulty connectors are usually a result of poor crimping in the installation process. For just this reason, I never used the typical hardware store variety of wire crimpers. It is my opinion that only a quality pair of ratcheting crimpers should ever be used on a boat. I actually have a couple of different pairs depending on what and where I am working. In addition, I have a heavy duty crimper for large cables, but they are very expensive, and unless you plan to do a lot of this type of work, not worth the expense, in my opinion. Another invaluable tool, is a circuit tester, especially working on older boats where previous owners have added and removed wiring without any identification. It allows me to chase down both ends of any wire and determine if it should be connected somewhere or removed. And of course, a good multi-meter is a must have on the boat at any time to troubleshoot or do repairs.

My first step was to be sure all power to the existing panel was disconnected. The shore power cord was completely disconnected and the main battery cables also removed. Since the battery cables were scheduled for replacement anyway, now was a good time to start the removal process. The biggest challenge is to keep track of which wires go where. The new panel was made for me by Paneltronics and is their 5401 analog model. I chose this one for several reasons. I have used Paneltronics line for a long time and always found them to be of very good quality. The 5401 would allow me to customize the breakers in any fashion I needed, and most importantly, the panel fit quite well in the space where the old panel came out. This meant I would not have to make any modifications to the bulkhead, which would add a lot of additional time and work to the project. In the process of removing the existing wiring, I carefully labeled each wire as to what load it feeds and was very careful to keep the DC and AC separated and easily identifiable. The original panel had the battery switch included, but the new panel would not, so all of the connections for the batteries were completely removed. This is very tedious, but an extremely important process. A small label-maker is very helpful at this time. This is also a good time to separate and organize the wiring if it looks like a plate of spaghetti before you start. It is also a good time to have a close look at all of the connectors and give each a good hard yank to be sure they are secure. Any that look suspect should be replaced, and all of them should get a cleaning and coating. I like CRC product for cleaning the connectors and adding a protective coating. Once all of the wiring was removed and sorted out, the old panel could be removed. The next step was to mount the new panel, and since the dimensions were very close to the old panel, this was the easiest part of the entire installation.

Once the new panel was mounted in place, all of that wiring had to be reconnected. If I had the time, I would do a complete rewire of the entire system. But since this would be a massive undertaking and that good old work thing takes up much of my time, I chose to only replace wiring that was suspect or that obviously needed to be replaced. There were quite a few, but fortunately, during many of our other projects, we have already replaced many runs. I generally start from the top of the panel, which in this case is the DC side, and work down. Once all of the DC is re-installed, the AC side is done. I did upgrade some of the wiring from the shore power inlets, from the number 10 wiring to number 8 on one of the inlets. Of the two, on the one we installed, we used number 8 wire. The shore power is connected via a transfer switch that feeds the panel from the shore power or from the inverter. The second shore power inlet only feeds the smaller AC sub panel that we installed earlier. This smaller panel only feeds the circuit for the air conditioning at this time, but we can add other circuits later if need be.

During the replacement of the panel, I also added new Blue Seas bus bars for the AC ground (green wires) the AC neutral (white wires) and the DC grounds. This cleaned up the wiring considerably, made all of the connections neater and gave me the chance to replace all of the connectors. Once all of the wiring was reconnected, everything was checked and double checked to be sure the right wire was connected to the right breaker and everything on the AC side of the panel was indeed AC, and the same for the DC side. With all of this completed it was time to move on to connecting the batteries to the DC side of the panel. 

The battery cables were the original copper wire cables that were installed by the boatbuilder. They were probably too small and were connected via two battery banks. My new house bank is combined to have all of the batteries make up a single large bank. This improves the efficiency of the house bank and increases the longevity. With this set up, there only needs to be a single cable from the house bank to the DC panel and a single on and off switch, rather than a 1,2 or a "both" switch that was on the old panel. In each installation, this might be different depending on the set up and the needs of the owner. Some like to have the start battery on the switch so it can be combined with the house bank in an emergency. I prefer to have the start battery totally separate and have a set of jumper cables in the engine compartment should this be necessary. With this set up, there is no danger of me forgetting to change the switch and killing all of the batteries. But this is a matter of personal preference. The run from the house bank to the panel is a short one, and #2 wiring is more than sufficient to make the connections. Both the positive and negative cables were replaced as was the battery switch. In calculating wire size, the maximum amps that can be carried on the wiring and the length of wire round trip, from the battery bank to the panel and back to the batteries, need to be factored in. Likewise the battery switch needs to be sized properly. An excellent calculator for wiring size can be found here. What works in our installation may or may not be correct for another. A good solid connection on the cable ends is also very important in making up these cables. Some installers like to do a combination of soldering and crimping on battery cables. Myself, I prefer crimping only, but it must be done right. This is where my serious cable crimpers come in to play. I also use a heat shrink tube on every cable connection to prevent internal corrosion and to keep the connections neat and clean. This is done on all connections to the batteries and with any wiring used in the bilge or a wet area. For smaller wiring I use heat shrink connectors. I do not use heat shrink connectors on smaller wire, other than battery cables, that connect on the panel. But that is just my choice, since these connectors are considerably more expensive. I also installed fuses on the battery terminals for added protection and security. These fuses must be sized correctly.

With all of the connections completed, the moment of truth is at hand. Everything has been checked, double checked and triple checked. For me, there is always a bit of anxiety in firing up an electrical panel for the first time, no matter how many times I have done it. For me, the DC is the least scary, so that is the one I check first. It was simply a matter of throwing the battery switch and then the DC main on the panel. The voltage meter registered fine, and there was no smoke or sizzle. You need to be cautious with electricity or electronics since they are driven by smoke. If you let out all of the smoke, they won't work. So far so good, and one circuit breaker at a time was switched on. Once again, no smoke escaped. Now it was time to check all of the connections and the entire DC side of the panel with my multi-meter to look for problems and anomalies. Everything looked just fine, and the battery voltage was holding correctly for the loads applied. Every circuit was tested and inspected. Next came the really scary part. The AC panel.

With all of the AC circuit breakers off and the transfer switch in the off position, the shore power cord was plugged in. Oh good, no smoke or sizzle. If that were to happen with either DC or AC, the power must be turned off immediately and the problem solved. Once the shore power was plugged in, the transfer switch was changed to the shore power setting and the main breaker turned on at the new panel. Once again, so far so good. One at a time the new breakers were switched on and the voltage meter monitored carefully. All circuits were tested with the multi-meter. This is where it is very important that you know what you are doing since you will be dealing with live 120-volt power. This is no place for the inexperienced and can in fact be life threatening. All of the circuits on the panel checked out fine, and each outlet on the boat was tested for correct polarity and for faults. A simple outlet tester will work just fine, however, some cheap hardware testers may show a fault when none exists. So be sure the problem, if one shows, is in fact the circuit and not the tester. All of the outlets on the boat checked out and none of the GFCI plugs tripped, a good thing. All of the appliances on board were turned on to be sure they all worked. The final step was to transfer from shore power, unplug the cords, and transfer to the inverter. The entire testing process was repeated until I felt comfortable that the system was operating safely and correctly. 

A couple of reference books that have been very helpful to me over the years is Nigel Calder's Boat Owners Mechanical and Electrical Manual and The 12 Volt Bible. Both are good for both getting started and for planning more advance work.


Finishing a major project like this gives me a real sense of satisfaction and a new comfort level that the electrical system is now even safer that it was before. There are many aspects of the system that still need some work and over time will get done. But for now, we are secure in knowing that a major portion of it is up to date and the components are new. In addition, should anything need to be repaired or any troubleshooting need to be done, we now have intimate knowledge of the systems and where everything can be found. Maybe for the next project I will tackle something a little smaller.


  1. How did you go about deciding what 12v devices each circuit breaker protected? I have some "multiples", e.g., VHF CB also controls the CD player added by the previous owner. Doesn't seem quite right.

  2. Brian, The new panel replaced one for one breaker on the old panel PLUS additional breakers for any multiple connections that had been done in the past. A couple of spares were also added for the future. Unless a circuit was very low amps, it got it's own breaker. Pretty much anything 3 amps or over. Chuck


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