Blue View – Adding a Fuse or Breaker

Last week we talked about the importance of fuses and breakers. Every energized wire should be protected from overheating or fire by using a properly sized fuse or breaker. This week's blog will talk about how I go about installing them.


I'll start with fuses, of which there are several styles and types. The simplest is the in-line AGC or MDL type fuse. Often, all that is needed to install an in-line fuse is a crimp type ring terminal on one end and a crimp butt connector on the other. The ring terminal is connected to the positive terminal post and the butt connector is connected to the circuit wire. These fuses range from 0.25 amp to 30 amps, and are available as either a fast acting or a slow-blow type fuse.

Automotive type fuses are also commonly used aboard. These are also in-line fuses and are connected the same way as the AGC/MDL fuses. These fuses range in capacity from 1 to 30 amps for the ATO and ATM series fuses and from 30 to 80 amps for the “Maxi” type fuses.

Larger capacity fuses that require a fuse block are also available, and range in value from 30 amps to 400 amps. I find a suitable location to mount the fuse block, then drill the holes for the mounting screws and secure it in place. The wires are cut to length and ring terminals are crimped onto the wires. The wires are then secured to the terminal posts, and the appropriate size fuse is screwed onto the mounting posts.

BVAddFuse Terminal Block.jpg

A very clever fuse made by Blue Sea attaches directly to a battery terminal. Their Battery Terminal Fuse Blocks can be used to connect one or up to four wires directly to the battery. It is a reasonable method for a simple boat system with one or two house batteries, but may be expensive and cluttered for a larger system like ours with six house batteries and many circuits.

If I think I will need to shut the circuit off at times, either to save power or for servicing, I prefer to use a circuit breaker with a toggle switch rather than a fuse. Most boats have a distribution panel with somewhere between five and fifty breakers. Ours has six AC breakers and twenty DC breakers. This seems like a lot, but as we added equipment and circuits, we soon ran out of breakers. I added an additional distribution panel with another six DC breakers, as well as a few individual breakers ,to handle such things as another bilge pump and both autopilots. These range from 5 to 50 amps.

BVAddFuse Breaker Panel.JPG

If I am adding a breaker to an existing distribution panel, the new breaker must be compatible with the panel (duh!). Usually, one terminal on the breaker screws directly onto the power bus on the back side of the panel, and the circuit wire screws onto the other breaker terminal. If the breaker is a freestanding individual breaker, a mounting bracket should be purchased or fabricated. I usually fabricate my own bracket using aluminum sheet metal cut to size and drilled to hold the breaker securely in place.

By the way, if you purchase any of the products above (or anything else for that matter) using our Amazon link, it costs you no more but adds a few pennies to our cruising kitty – which is always appreciated.