The Electrical Side of Boating


Ignition Protected Components Circuit Protection and More By Jack and Alex Wilken


Last month we discussed some


of the materials needed to produce a professional marine wiring job. Now let’s talk about other parts we did not cover before, again with the idea of providing information which is either helpful or critical, but not a complete treatise on marine wiring.


Color Amperage Code blade fuses


Black Gray Violet Pink Tan


Brown Red


Lt. Blue Yellow Clear Green Amber Orange Natural


ATC ATM MAX 1 2 3 4 5


2 3 4 5


7.5 10 15 20 25 30 40


7.5 10 15 20 25 30


50 60 20


30 70 40 80


Figure 1: Blade type fuses can be identified by their color.


One theme that runs through all


this is that some electrical components need to be Ignition Protected (IP). The American Boat and Yacht Council refers to IP components as those that do not cause a spark that would ignite an air/gas mixture, or that their surface temperature would get hot enough to ignite an air/gas mixture. Components


Figure 2


or equipment that can cause a spark are not to be put in spaces where gases can accumulate (gasoline engine spaces, propane systems, etc). Circuit Protection is another


important issue, mainly, so you do not have a fire. All the components in a circuit must be able pass the maximum amperage test without heating up to temperatures that can melt insulation or parts. If you lose the insulation, you can have a short circuit where the positive and negative poles of the battery are directly connected together at the wires without doing any work or being protected. I have seen nearly the perfect short circuit when someone dropped a crescent wrench across the unprotected terminals of a 100 amp battery which resulted in instant explosion, sending acid flying up 6 feet in the air! Luckily, no one was hurt. The idea is that battery poles are only connected through circuits that have amperage limiting devices in them (lights, motors, etc), and are protected by a fuse or circuit breaker which is as close as possible to the source. Circuit breakers are covered in this article only in the part about ground fault devices. On to Specifics Fuses and Fuse Holders should


There is an interesting variation called the Smart Glow Fuse which “only glows when it blows”. These fuses can be difficult to remove so have the extractor tool made for the job handy. (Figure 2) All that said, these fuses are easy to identify and to replace if you use the extractor. Some people prefer the older glass tube type fuses. If you choose these, do not buy the cheapest available because all these fuses have caps that are soldered and need to be of the highest quality because they can be subjected to high temperatures. Both types have inline or mounted holders available. In the case of the mounted fuse holder, look for ones that have screw terminals that accept eye crimp fittings. Also, some fuse holders incorporate a ground or negative buss. (Figure 3) These should have a cover to protect against shorts from something


Figure 3


Fuse Block incorporating negative buss bar, high and low load fuses, and Ignition Protection cover.


Tool easily


removes and replaces blade type fuses.


48° NORTH, SEPTEMBER 2011 PAGE 34


be sized to protect the wiring. Fuses are not, in most cases, considered IP. This means mounting them in spaces that could accumulate explosive gases ought to be a no no. A solution for this is to use a fuse holder which is sealed so any spark would be contained. Automotive DC systems have brought us the ATO/ATC fuses and their larger counterparts. These fuses are rated to 32 volts, so they are usually used only in 12v or 24vdc systems. (See the chart for color vs ampere rating in Figure 1.)


accidentally coming in contact with one of the circuits. If the manufacturer of the equipment you are installing requires a fuse for the equipment, then the wire needs to be large enough so that the fuse used for the equipment more than protects the wire. The chart in Figure 4 shows the first consideration which is maximum fuse size to wire size. Use of a smaller size fuse is always safe, but remember that there are two factors in the selection of wire size, the second being voltage drop caused by the length of the circuit. An online resource for voltage


drop is http://bluesea.com/resources under online tools, or ABYC has published charts for voltage drops


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