Selecting the proper fuse for your application is arguably one of the most important tasks when it comes to your boat’s electrical system. There are a lot of choices out there, and sometimes it can be overwhelming.  Here are some important factors to consider when selecting the proper fuses.

Maximum Voltage Rating

One important requirement for selecting a fuse for your application will be the voltage rating necessary to properly protect the equipment. Most common fuses are rated for a maximum voltage of 32 volts DC while some (like the Class T fuse) are rated typically up to 125 volts DC. When it comes to marine electrical systems, the nominal boat voltage is 12 and/ or 24 volts DC but with emerging technologies like electric propulsion and solar becoming more popular,  more systems will likely be rated at 48 volts DC or higher.

Maximum Amperage Rating

Another important factor in selecting the proper fuse for your application is the amperage rating required to protect the wire and the equipment. Almost all reputable manufacturers of inverters, inverter/chargers, and battery chargers will provide a recommended fuse rating in their owners manuals.

ABYC E-11 states that the overcurrent protection device should be rated at no more than 150% of the ampacity of the conductor. What this means is that a 30 amp DC load with the proper conductor size shall be fused at no more than 45 amp DC. The exception to this rule is on motor circuits (like a bilge pump) where a situation called the Locked Rotor Scenario can occur. When this occurs, the bilge pump motor may have some trash blocking it from turning. If the manufacturer's exact fuse recommendations aren’t followed, the pump could continue to overheat and begin to melt - possibly creating a fire on board.  An oversized fuse would not be blown in this situation.

Interrupt Capacity

Interrupt Capacity is a rating that is especially important on inverter installations. Commonly, this is referred to as an AIC rating - which is the fuse's ability to blow without locking or welding itself to a permanently closed position, thus allowing for an extreme amperage flow through the fuse. A good rule of thumb is that the AIC rating of a 12 or 24 volt DC inverter installation should be 12 times the amp-hour capacity of the battery bank that the inverter is connected to.

For instance, if you have four Group 31 batteries in a 12 volt inverter installation that have a 100ah capacity each (for a total of 400ah), then the fuse's AIC rating should be higher than 4800 (12 x 400 = 4800).

Almost all inverter installations will require the use of a Class T fuse that is rated typically for 20,000 AIC.

Ignition Protection

The final important factor when selecting a fuse is if its necessary for the fuse to be ignition protected.  If a fuse is to be located in a gasoline engine room, then it must be ignition protected.

 

If you have any questions about the proper equipment for your boat's electrical system, please give the experts at Marine Parts Source a call at (866)388-0390.