Marine Circuit Breakers, Fuses, Panels and Terminal Blocks overview

What is Marine Circuit Protection?

All boats, regardless of size or sophistication, are required by regulation to have circuit protection on every positive wire outside of the engine starting circuit. If an electrical circuit is overloaded with excess current, the wire insulation can melt with a fire the likely outcome. Circuit breakers and fuses are designed to protect the wires in all main and branching electrical circuits.

CIRCUIT BREAKERS: Are an automatic safety switch that protects an electrical circuit from overload and subsequent catastrophic failure. Similar in function to a fuse, a circuit breaker can be reset after tripping. Marine circuit breakers are actuated magnetically or thermally and they also incorporate a manual switch that can be used to shut off specific circuits. Circuit breakers are typically grouped together as a cluster and mounted in a suitable breaker panel. Panel mounting of circuit breakers provides for an organized and easily serviced electrical system. Circuit breakers are designed to protect circuits- not equipment.

CIRCUIT BREAKER TYPES:

The Push Button Reset-Only Circuit Breaker is an economical choice when circuit switching is not needed or is operated in a different location. This style of circuit breaker is typically available in amperage ratings from 3 - 60A. The Reset-Only type is a "Trip-Free" design which means that it cannot be held ON during a fault current condition.

The Toggle Switch Circuit Breaker combines switching and circuit protection into a single unit. Single pole circuit breakers are typically used for protecting DC or AC branch circuits. Double pole circuit breakers are often used for 120 Volt AC Main circuit protection. Triple pole circuit breakers can be used for 240 Volt AC main circuit applications. This style of circuit breaker is also a "Trip-Free" design which means that it cannot be held ON during a fault current condition.

The Rocker Switch Circuit Breaker also combines switching and circuit protection into a single unit. The Rocker Switch style is available in Flat Rocker, Restricted OFF Rocker and Raised Rocker configurations. Single pole circuit breakers are typically used for protecting DC or AC branch circuits. Double pole circuit breakers are ofter used for 120 Volt AC Main circuit protection. This style of circuit breaker is also a "Trip-Free" design which means that it cannot be held ON during a fault current condition.

• Flat Rocker: Resists accidental switching by being flush in the ON position.
• Restricted OFF Rocker: Can only be switched to OFF by insertion of a small screwdriver into a slot.
• Raised Rocker: Resists accidental switching by being flush in the ON position.

The Residual Current Circuit Breakers (GFCI and ELCI) functions as a Ground Fault Circuit Interrupter (GFCI) and as a Equipment Leakage Circuit Interrupter (ELCI). These devices provide protection for shore power connections (AC) and can reduce electrocution risks to persons on the boat, at the dock and in the water.

FUSES: Are another version of an automatic safety switch that protects an electrical circuit from overload and subsequent catastrophic failure. Similar in function to circuit breakers, fuses are designed fail when the current in the circuit exceeds the amperage rating of the fuse. The wire in the fuse melts and breaks the circuit leaving it in an open condition. Fuses are available in numerous styles and amperage ratings.

Panel mounting of fuses provides for an organized and easily serviced electrical system. Fuses are also found on most electronic devices either built into the housing or in the positive feed wire. Fuses are designed to protect circuits and equipment, if installed correctly. Generally fuses are available in lower range of amperage ratings making them ideal for protecting sensitive electronic equipment.

FUSE TYPES:

The glass-capsule fuse has been in use for many decades. Glass fuses generally consist of a glass tube with metal caps on both ends. A strip of metal joins the two caps and is visible through the glass tube. The metal strip is the actual fusible material - it is the sacrificial element that melts when the current draw exceeds the fuse rating. Glass fuses are sometimes thought to be "old-fashioned" - however, they are simple, reliable, low in cost and readily available. Glass fuse designations: AGA, AGC, GMA, MDL, SFE.

Advantages of the glass-fuse:

• Easy to find, spare fuses are inexpensive.
• Fuse condition is usually easy to see.
• Glass-fuse style fuse blocks are inexpensive as compared to circuit breaker blocks.

Drawbacks of the glass-fuse:

• Fuse length is often related to the amperage rating. It may not be possible to use a different amperage rated fuse in an existing fuse holder.
• A special tool is needed when removing fuses from a fuse panel without breakage.
• It is possible for the metal strip to melt inside the cap where it is not easily seen.
• Fuse ratings are typically marked on the metal caps. It is often necessary to remove the fuse from the block to read the markings.
• Constructed from glass, this style of fuse somewhat fragile- handle and store with care.

Blade type fuses (also called spade or plug-in fuses), are constructed with a transparent plastic body and two flat blades that fit into fuse block sockets. They are typically found in automotive and marine applications. Each fuse is printed with the Rated Current in Amperes on the top. The plastic body is conveniently color coded to further identify the amperage rating. These types of fuses come in four different physical dimensions: low-profile mini (APS), mini (APM / ATM), regular (APR / ATC / ATO), and maxi (APX) heavy-duty. Blade type fuses are rugged, compact and easily replaced without tools.

Advantages of the Blade-fuse:

• Easy to find, spare fuses are inexpensive.
• Easy to inspect. Test points are built in.
• Fuse amperage ratings are clearly printed on the end.
• Color coding visually confirms amperage ratings.
• Can be stored and handled without breakage.
• Less expensive than circuit breakers.

Disadvantages of the Blade-fuse:

• Must be pulled from the fuse block for inspection.
• More costly than glass fuses.
• Fuse blocks are more expensive than glass types.

Typical Amperage Color coding of ATM, ATO/ATC Blade-fuses:

• Gray: 2 amp
• Violet: 3 amp
• Pink: 4 amp
• Tan: 5 amp
• Brown: 7.5 amp
• Red: 10 amp
• Blue: 15 amp
• Yellow: 20 amp
• Clear: 25 amp
• Green: 30 amp

Other common Fuse designations and features

MIDI or AMI Fuses: A compact fuse for main or branch circuit protection.

• Clear window offers visible indication of blown condition.
• Color-coded for easy amperage identification.
• Interrupting Capacity: 5,000A
• Maximum Operating Voltage: 32V DC

MRBF Terminal Fuses (Marine Rated Battery Fuse): A space-saving ignition protected fuse for 30 to 300 Ampere loads. Must be used with a matching Terminal Fuse Block.

• High interrupt Rating satisfies ABYC requirements for DC Main circuit protection on large battery banks.
• Clear window offers visible indication of blown condition.
• Color-coded for easy amperage identification.
• Interrupting Capacity: 10,000A @ 14V DC; 5,000A @ 32V DC; 2,000A @ 58V DC
• Maximum Operating Voltage: 58V DC

MEGA or AMG Fuses: Used with matching MEGA or AMG fuse blocks for an economical system for 100 to 300 Ampere circuit protection.

• Interrupting Capacity: 2,000A
• Maximum Operating Voltage: 32V DC

Class T Fuses: Used with matching Class T fuse blocks for circuit protection of devices including converters.

• Interrupting Capacity: 20,000A
• Maximum Operating Voltage: 160V DC
• Extremely fast short-circuit response
• Recommended by inverter manufacturers
• The only UL 248-15 listed fuse commonly available in the marine industry.

ANL Fuses: Used with matching ANL Fuse Blocks for many applications with 35-750 Ampere loads.

• Interrupting Capacity: 6,000A
• Maximum Operating Voltage: 32V DC
• Silver-plated connector blades for corrosion resistance.
• Visible indication of blown condition.
• Lower cost than Class T Fuses.
• Available in a wider amperage range than Class T Fuses.
• Ignition protected - safe for use aboard gasoline powered boats.

A well designed electrical system incorporates circuit breakers and fuses in order to protect the electrical wiring circuits along with the equipment connected to it.

NOTE: The U.S. Coast Guard and other regulatory agencies require all circuits, except the starting circuit, to be protected with a circuit breaker or a fuse.

Power Distribution Panels

Power Distribution Panels are at the heart of a boat's electrical system. Current flows from a power source to a panel and is distributed to various loads throughout the boat. Most panels provide switching functions along with circuit protection (fuses and or circuit breakers).

CIRCUIT BREAKER PANELS: Are available assembled and wired from the manufacturer with an array of circuit breakers, panel meters, indicator lights, battery switches, switch labels, etc. These fabricated panels are offered in a wide variety of configurations, sizes and voltages (DC, AC, or both).

FUSE SWITCHING PANELS: Are available assembled and wired from the manufacturer with an array of fuses, switches, indicator lights, switch labels, etc. These fabricated panels are offered in a wide variety of configurations, sizes and voltages (DC).

ABOVE DECK PANELS: Are ruggedly designed for exposure to the elements. Available with fuses or circuit breakers these waterproof panels are typically installed in open helm applications.

BELOW DECK PANELS: Are available with fuses or circuit breakers and are suitable for use as extensions to existing panels or as replacements. These panels are not for use above decks or in exposed locations.

CONNECTORS and INSULATORS

• Terminal Blocks: Also known as barrier strips, terminal blocks connect wiring harnesses together without the need to make permanent splices. Terminal blocks also can be used to terminate multi-conductor cables which can then be split off to service separate loads. In marine applications terminal blocks are ideal for interior and navigational lighting systems. Terminal blocks make it easier to service wiring connections and more convenient to add a another branch to a circuit. It is a good practice to install a larger terminal block with a few empty spaces to allow for future added circuits. Each screw is connected electrically to the adjacent screw. Barriers between screw pairs isolate and insulate each wiring connection from the next. Terminal block jumpers simplify combination of separate circuits. Typically, terminal blocks are used for lower amperage connections.
• Busbars: Are typically used in higher amperage circuit applications. Busbars can be utilized to distribute positive wires or to collect negative return wires. Some busbars are designed to handle both positive and negative circuits. Many busbars incorporate an insulating or protective cover to prevent accidental contact or short circuits. Most busbars feature multiple connections that simplify power distribution circuits.
• Powerposts: Are similar to busbars in that they are typically used in higher amperage circuit applications. Powerposts feature a large stud that is designed for multiple heavy duty battery cable connections. In some configurations, powerposts may include terminal screws that accept smaller wire connections. Powerposts are usually more compact than busbars making them ideal for applications where access is tight.

Marine Electrical Resources

Boatowner's Mechanical and Electrical Manual 3rd Edition, by Nigel Calder, is an excellent resource and an essential troubleshooting guide for any boater, from the extreme novice to seasoned veteran. If it is on a boat and has screws, wires, or moving parts, it is covered in the Boatowner's Mechanical and Electrical Manual. Nigel Calder provides comprehensive advice on: battery technologies, 12 and 24 volt DC systems, corrosion, bonding & lightning protection, generators, inverters, battery chargers, electric motors, electric lights, marine electronics, antennas, RFI, diesel engines, transmissions, shaft brakes, and propellers.

Electrics Companion, by Pat Manley, will help you figure out how much energy you are consuming and how much each item uses per day. Most of the equipment we 'switch on' consumes electricity, even the panel lights and voltmeter all add up. Author Pat Manley's guide will help you understand your battery capacity and charging requirements.

Simple Boat Electrics, by John Myatt, contains all the information needed to troubleshoot 12-volt electrical systems. It explains how to locate a fault, correct the problem when you can, or adopt a "get-you-home" solution if you can't. Provides some basic theory so you can understand what you're doing with a special emphasis of seamanlike practice of anticipating and preventing trouble.

Arco Electrical Technical Manual, is packed with information to help you become more proficient in servicing sophisticated marine electrical systems. The Arco Electrical Technical Manual explains the fundamentals of troubleshooting electrical systems. Written in easy to read style with lots of illustrations and examples. Written by mechanics for mechanics.

12 Volts Made Easy - DVD, is a nuts and bolts 12 volt electrical systems primer that is presented in a clear and easy manner. Subjects covered include: basic electrical theory, circuits, battery maintenance, basic wiring diagrams, controls, transducers, recharging, marine components, lights, motors, troubleshooting, basic repairs, installations, and more. Running Time: 60 minutes.

The 12 Volt Sailor - DVD, will help you to learn how to design and build an efficient electrical system for any vessel. This program illustrates how to integrate the radar, watermakers, windlasses, single side band radios, auto pilots, and GPS devices into any D.C. System. Running Time: 45 minutes.