If I had to pick the most critical component of your boat’s electrical system, it would be, without a doubt, Overcurrent Protection. This topic is so important to me, it has made me quite flustered about how to best approach it. After many various rough drafts and ideas, I decided it would be best to break this topic into three articles. Fuses 101, Circuit Breakers 101, and How to Properly Fuse a Boat Circuit 101. Hopefully breaking up this topic into sections like this will make it easier to learn such critical information.
Basic Terminology:
Overcurrent Protection: A form of protection against excessive amounts of current traveling through conductors and equipment.
Overcurrent Protection Device: A piece of equipment designed to protect against an excessive amount of current traveling through a conductor(s) and or equipment. You may see this term listed as “OCP” or “OCPD”. Fuses and Circuit Breakers are the two major overcurrent protection devices on the market today.
Circuit Breaker: An automatically operated electrical device designed to protect an electrical circuit from damage due to a short or overloaded circuit. Like fuses, there are many different types and styles and will list them later in this article.
Circuit Breaker Terminology and Acronyms:
Voltage Rating: This rating specifies what the maximum voltage is for the circuit breaker without affecting the Amperage Interrupting Capacity (AIC. See below for definition). Circuit Breakers may also be made for the use of AC (Alternating Current) circuits only.
Rated Amperage: Also called the Tripping Amperage. This is the nominal amperage rating of the circuit breaker. This nominal rating is to inform you at what amperage the circuit breaker will trip. We use the term “nominal” as all circuit breakers can and do carry slightly more current than this rating. Usually, the tripping point of a circuit breaker is 125% to 140% above the nominal rating.
Amperage Interrupting Capacity (AIC): The max amperage the circuit breaker can safely handle and interrupt (aka trip) at the circuit breaker's rated voltage. If the amperage is to exceed this AIC, the circuit breaker may become faulty and allow the current to “arc over” aka allowing current to still flow within the circuit. If the circuit breaker is being used under the maximum voltage rating, the AIC will be higher by an unknown amount.
Trip Time: The duration of time it takes the circuit breaker to open aka trip. This is very much like the melting time of the fuse. The higher the current above the nominal amperage rating, the quicker the circuit breaker will open (trip).
Manual Reset: A type of circuit breaker which makes it so if a circuit breaker trips, it remains tripped until an individual investigates the circuit and physically resets the circuit breaker.
Trip Free: A type of circuit breaker that will trip or remain tripped, even if the actuator is physically held in the ON position.
Thermal Circuit Breaker: This type of circuit breaker operates based on heat. The current creates heat. As the current rises, so does heat. Once a certain temperature is reached, this circuit breaker will trip. The quicker the heat rises, the quicker the circuit breaker will trip.
Magnetic Circuit Breaker: This type of circuit breaker operates based on the magnetic field of the circuit. Current produces a magnetic field. The stronger the current, the stronger the magnetic field. The stronger the magnetic field becomes, the quicker the circuit breaker will trip.
Single Pole Circuit Breaker: A type of circuit breaker which has a total of two termination points for one single current carrying conductor.
Double Pole Circuit Breaker: A type of circuit breaker which has a total of four termination points for two current carrying conductors.
Single Throw Circuit Breaker: A type of circuit breaker which has a total of one actuator present on the exterior of the circuit breaker.
Double Throw Circuit Breaker: A type of circuit breaker which has a total of two actuators present on the exterior of the circuit breaker.
Push Button Reset Circuit Breaker: As the name implies, this circuit breaker has a “button” that will pop out when the breaker trips. To reset, you push the button back in. This type of circuit breaker is also called a “Flat-Pak Circuit Breaker” and “CLB Series”. They most often come in a manual reset, trip-free, single pole, thermal type. You can typically find these circuit breakers ranging from 3A to 60A.
Medium Duty Push Button Reset Circuit Breaker: This circuit breaker is very much like the one above, but a bit more robustly, allowing a higher nominal amperage range. They most often come in a manual reset, trip-free, single pole, thermal type. You can typically find these circuit breakers ranging from 15A to 60A.
Short Stop Circuit Breaker: This is most often a thermal type of circuit breaker which is enclosed in either a metal or plastic casing with two metal studs for ring terminal connections. These circuit breakers come in various types of resets. From auto-reset to manual-reset. You can typically find these circuit breakers ranging from 5A to 50A.
187 Series Circuit Breaker: This series is most often a manual reset, trip-free, single pole, thermal-type circuit breaker. This series circuit breaker has a manual trip function. All you do is slide the yellow arm to the position you wish it to be in (On or Off). You are simply using this circuit breaker as a switch for that specific circuit. You can typically find these circuit breakers ranging from 25A to 200A.
285 Series Circuit Breaker: This series is most often a manual reset, trip-free, single pole, thermal-type circuit breaker. Most come with a “Push to Trip” feature. This feature is a small button you can press on the circuit breaker which trips the circuit breaker. Now that specific circuit is no longer live. You simply turned it off. You are utilizing the circuit breaker as a switch. Can find them in both surface mount and panel mount configurations. You can typically find these circuit breakers ranging from 25A to 150A.
A-Series Circuit Breaker: This series is most often a manual reset, trip-free, magnetic-hydraulic type circuit breaker. They have quite a few options when it comes to the actuator. Plastic toggle, metal toggle, flat rocker, and raised rocker. This series circuit breaker may be utilized as a switch by simply moving the actuator arm from either position. This series circuit breaker is also available with up to a six-pole configuration and multiple delay types. Multiple terminal types as well. You certainly have options with this series circuit breaker. You will most likely find these circuit breakers in the plastic toggle configuration on breaker panels aboard a boat. You can typically find these circuit breakers ranging from 2.5A to 50A.
C-Series Circuit Breaker: This series is most often a manual reset, trip-free, magnetic-hydraulic type circuit breaker. They have quite a few options when it comes to the actuator. Plastic toggle, metal toggle, flat rocker, and raised rocker. This series circuit breaker may be utilized as a switch by simply moving the actuator arm from either position. This series circuit breaker is also available with up to a six-pole configuration and multiple delay types. Multiple terminal types as well. You certainly have options with this series circuit breaker. You will most likely find these circuit breakers in the plastic toggle configuration on breaker panels aboard a boat. You can typically find these circuit breakers ranging from 5A to 300A.
As you can see, there are a plethora of circuit breaker options for your boat circuits. I also just scratched the surface of what is available out there when it comes to circuit breakers. I simply provided information on the circuit breakers I see routinely used aboard a boat and readily available. Yes, it may seem a tad overwhelming, but I assure you it is not. It is good to have options. With so many options, it is practically impossible to not be able to provide over-current protection to your boat’s circuits.
If I could only ask two things out of you, it would be:
- Please provide Overcurrent Protection to your boat circuits.
- When choosing a circuit breaker, please read the included spec sheet of the circuit breaker and base your choice on such. Do not base your choice on price and what is readily on hand.
Well, that concludes this article. I hope it was informative for you. If not, I hope it was enjoyable to read. If you have not already, I encourage you to go on and read the following two articles: Fuses 101 and How to Properly Fuse a Boat Circuit 101.