Marine Electrical Safety: Boot Those Terminals
Question: The other day I opened the engine hatch on my new sailboat to check my engine oil. While I was poking around in the engine I noticed the part shown in the photo here. It looks like a fuse of some sort. My concern here is that the terminals are completely exposed as you can see in the photo.
This area is normally covered up with the engine box but I still think this may be a bit dangerous if a metal part were to come askew and make contact with those wire studs. What do you think?
Answer: This is a question that has come up before in a slightly different context. (See Boat Storage and Bow Thrusters.) Protective boots are required to cover starter and alternator primary DC terminals, and they’re required here as well. The bottom line based on ABYC standards is that any terminal that is on the live DC side of an electrical circuit that is not protected by a fuse or circuit breaker at its source must be protected by a protective cover or boot.
This all gets a bit confusing in this case because in fact the item in your photo is a fuse. But rest assured, there is still some danger here. If a metal object were to come in contact with either terminal or both terminals simultaneously and short out by also coming in contact with the nearby engine block, sparks are going to fly! It’s hard to see in your picture, but I think it says 350 amps on the fuse. That is really high current, and the cables shown can carry a lot more than that if a short circuit does occur. In a situation where a short circuit from either terminal to a metal part on the engine might occur, the fuse would not blow and really high electrical current will flow until either the cable burns up or someone gets the power turned off.
The bottom line here is that this fuse and its terminals should have insulating boots or a cover over them to eliminate any short circuit possibility, even inside the engine box.
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