Any boat built to NMMA (National Marine Manufacturer’s Association) standards has circuit protection for its boat wiring system. These breakers/fuses are specified to provide adequate amperage for all standard equipment. And, the original boat wiring is sized for the factory installed system.

Problems occur when the boat owner or dealer begins to add other items.

The best and safest position to place your circuit protection is as close as possible to the source of power (battery or distribution panel). For example, a new fish finder is added to the helm of a boat. There isn’t an obvious way to splice in the existing boat wiring to connect the power and ground wires. The solution is to run a new pair of wires to the battery. The fuse for the fish finder needs to go as close as possible to the battery. The fuse is protecting the fish finder and its wiring. If the fish finder has an internal fault, the fuse will blow. If the wire between the fish finder and the battery gets damaged, the fuse will blow.

If the fuse is installed close to the fish finder, then in the case where the wire is damaged between the fish finder, the wire will burn instead.

Circuit protection is also very important when adding additional charging sources. This new charging source is considered to be a source of power that needs circuit protection. If it is not a “self limiting” device, circuit protection is needed at both ends of its positive output wire. Most chargers are self limiting.

For example, let’s say that a solar battery charger is added to boat. It has 4’ long leads with an inline fuse 7” from the end of the positive lead. The boat owner needs to add 8’ of wire to allow the charger to be connected directly to the battery. As long as the wire doesn’t get damaged, this setup will work fine.

Problems occur when the wire gets damaged. If the wire is damaged between the charger and the inline fuse, the self limiting battery charger will shut down, and the blown fuse will limit the output of the battery. If the wire is damaged between the inline fuse and the battery, the battery will continue to discharge until it is depleted or the shorted wire has completed burned up. This usually results in a fire.