Damien; actually you caught me in the middle of preparing a page for my web site on planning an electrical system
. I have hesitated to put it up here because it is by no means finished, there's a lot left out, and it's pretty basic, but what the heck. This is a question that comes up very frequently on boating
forums so if it helps, here goes.
For the rest of you if you have any suggestions for additions or corrections feel free. I haven't posted it on my web site yet and probably won't for a while so have at it. Be Merciful! My ego bruises easily (LOL)
Damien you can ignore the first paragraph:
Planning the Electrical System:
If you are building boats for the purpose of sale
, you should have a professional design and install the electrical system. This will save you a lot of headaches in the long run. It will work better, longer and with fewer problems. But should you want to do this yourself then it is extremely important that you have a good understanding of what you are doing. The basics of electricity and electrical systems are not hard to understand. But if the system you are installing goes beyond simple DC then you should go to a professional. Keep in mind, most fires on boats are electrical fires. Do it right or not at all.
You should start by reading and studying Basic Electricity There are many books available and on-line resources. There are also courses available. (IKE'S LIST)
Once you have an understanding of the basics and the terminology then you can begin planning the electrical system on your boat. I am going to discuss only DC in this paper. Please keep in mind, this is not a detailed tutorial of the process. This is only a general overview of the process.
Determine your needs. What electrical equipment
will you be using? There are some basic things:
What else? If this is a small boat for fishing
, maybe you have a trolling motor
and a depth sounder
If it is a much larger boat or a cruising sailboat or powerboat you may have even more equipment.
Anyway, the list goes on. List all of the equipment. This list helps you determine the loads (how much power each item uses) and how much power you will need to run it. This determines how big your battery bank will be. It also determines the size of the fuses
or circuit breakers for each branch of the electrical system. (Glacier Bay Battery Bank Load Analysis)
Also, do you need a starting battery and a separate bank of house batteries? Also how are you going to charge the batteries? (Batteries and Chargers)
. Determine where the equipment will be on the boat. Draw a Diagram showing the general arrangement and where everything will be.
This determines how long each wire has to be and helps in determining the wire size. It also helps to determine the route
of the wire through the boat. Remember, wire cannot go through solid objects like pipes and vent ducts, and other equipment. It has to go around such things. It should not just be strung through the boat and it should not be in the bilge
. It should be fastened down at 18 inch intervals or less. And don’t forget the return run. There are two wires; positive and negative.
Where will your battery bank be? Put this on the diagram. It needs to be in a dry warm place. It should not be in the bilge, or anywhere exposed to water, but because batteries are very heavy they need to be low in the boat. They need to be in a space that is ventilated. Most boats have them near or in the engine space, this is good but there are rules about the placement of the batteries (Electrical Regulations
) near fuel lines and other equipment.
Where will the fuse or circuit breaker panel be? Put this on the diagram. Again, there are rules about placement of fuses and circuit breakers in relation to the source of power. (Electrical Regulations
On/OFF Switches? Where will they be? Some are on the instrument panel. Others are near the piece of equipment. Some are built into the equipment. Show on the diagram where they will be. Also, will you have more than one on/off switch ? Example: Cabin
lights, do you want a switch at both ends of the cabin, or will each individual light have its own switch? Where this really gets complex is navigation
lights especially if you have combination anchor/running lights with more than one bulb in the fitting, or more than one filament in the bulb.
Where will the battery shutoff switch be? This needs to be very close to the battery bank but easily accessible. It especially needs to be where you can shut it off in the case of an engine room fire or flooding.
What items need to be directly wired to the battery and not through the switch? There are some things on a boat that you do not want to shut off when you turn off the battery switch, such as the automatic bilge pump
, or an automatic fire fighting system.
Determine wire sizes for each wiring run. This is determined by a combination of the amperage (the load) and how many items are on the circuit. (Wire Size)
This also determines the size of the fuse or circuit breaker. If you have a very long run you may have to go up a size in the wire to prevent voltage drop
. Don't forget to follow the wiring color codes.
Use your diagram and other information to begin drawing a schematic of the system. Show the ground. On most boats the ground is the engine block. Also determine if you are going to have a grounding buss for the DC system. This is a green wire that runs through the length of the boat that connects all of the metal cases of the electrical equipment to the main ground. This is not the same as a bonding system.
On the schematic show where busses and fuse blocks go. A bus is a solid metal conductor that has many posts on it for circuits coming off the buss, but only one connection to the source of power. In a DC system if you use busses, you need both positive and negative busses. A typical buss.
After you get the schematic laid out show the schematic to someone with a marine electrical background, and ask them to look for any problems.
The schematic is just a representation of the electrical system. It does not, and should not look anything like the boat. That is what the diagram of the general arrangement is for.