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If you own a fairly new boat, either power or sail, you undoubtedly have a few or perhaps many of these fuses in service on board. I recently had the pleasure of attending a brief presentation from one of the better known manufacturers of these fuses, Littlefuse Co. The crux of the presentation was all about whether or not these fuses are considered to be rated for ignition protection. This, for anyone who follows, is an important point for gasoline fueled boats or fuses installed in battery storage areas; anywhere on board your boat where if things were to go wrong like over charging batteries or a gasoline fuel leak could create a volatile fuel air mixture. If the fuse were to blow it might just cause an explosion.

Well the short answer here is that these fuses have been tested and do pass ignition protection tests. The reason this was in question in the first place has to do with the fact that some of these fuses  have an open bottom as shown in this next photo:

ATO Fuse2


The question has been whether or not this open to atmosphere situation found on some, but not all fuses of this type was dangerous and in fact not rated for ignition protection. Well the small, lower amp rated fuses of this type are rated for ignition protection! I spoke with Bob White, who owns and operates Imanna Laboratory in Florida since he is the person who actually performed the necessary tests and he explained why this was the case. If you look closely at one these fuses you’ll see that the fuse element inside the plastic housing arcs upward into the plastic housing. According to Bob, because of this upward slope, any arc when the fuse blows stays contained inside the plastic housing and keeps the worst from occurring in the event of gasoline vapor or hydrogen gas build up.

So, that’s the good news relative to the class of automotive type fuses branded either ATO or ATC. That said, the presenter from Littlefuse Co. also pointed out that some of the higher amp rating fuses that look like the ATO/ATC style, did not pass ignition protection testing. So, beware and double check this installers!

Finally, I’d like to remind folks that there is some sorted history out there regarding cheap imitations for these ATO/ATC fuse types that have elements inside that are made of aluminum, which is not ABYC compliant. I have personally found some of these supplied with electrical equipment I’ve installed over the years and in the salt air environment where I do most of my boating, the aluminum corrode and failed in about one boating season. Un-anodized aluminum does not hold up well at all in a saltwater environment!

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