M & I Systems, Inc.
4200 Aurora Avenue N.
Seattle, WA 98103
Info: (206) 547-7899
Fax: (206) 547-8875
Circuit Protection
Generally, there are three types of devices used for circuit protectors:
Each device has its own advantages and disadvantages, especially in marine use.
Fuses
Fuses can be an inexpensive, dependable means of protecting equipment and wiring. They can be especially cost effective when high current interrupting capacity is required. Their main disadvantage is that they destroy themselves in the protective process. This can be a catastrophic disadvantage when at sea and away from a source of replacement. Often, when a fuse of the proper value is not available, a fuse of another value is substituted, compromising safety and equipment.
Note: Currently M & I Systems does not stock any fuses except those used in special applications on custom panels built in our facility.
Thermal Breakers
Thermal circuit breakers use a bimetallic strip electrically in series with the circuit. Heat generated by a current overload deforms the bimetallic strip and trips the breaker. Thermal breakers have a significant advantage over fuses because they can be reset after tripping. The main disadvantage of thermal breakers is that they are "heat sensing" devices and their performance can be adversely affected by changes in ambient temperature. When operating in a cold environment, they will trip at a higher current level than their rating and conversely, when operating in a warm environment, they will "nuisance trip" at lower current level. Either condition can compromise safety. Thermal breakers have relatively slow trip times as compared to fuses or magnetic breakers.
Thermal breakers can be made water-resistant with optional rubber caps. Manual reset push button thermal circuit breakers are stocked by M & I in 5, 7, 10, 15, 20, and 25 amps.
Magnetic Breakers
Magnetic circuit breakers provide advanced solutions for the marine industry. They have all of the advantages of thermal circuit breakers but none of their disadvantages. They are temperature stable and thus not appreciably affected by changes of current in the circuit being protected. They have no "warm-up period to slow down a response to an overload and no "cool-down" period after an overload before it can be reset. The magnetic breakers offered by M & I Systems all feature a safety feature known as "trip-free" operation which makes it impossible to manually hold the contacts closed during over current or fault conditions. In the case of multi-pole breakers, a common trip linkage between all poles ensures that an overload in one pole will trip all adjacent poles.
The C-Series UL489 circuit breaker is specifically designed for those applications requiring higher amperage and
higher voltage handling capacity in a smaller package. These breakers employ a unique arc chute design which results in obtaining higher interrupting capacities, up to 10,000 amps. New thermoset glass-filled polyester half shell construction provides for increased mechanical and electrical strength. Wiping contacts, mechanical linkage with two step actuation, and clean contacts provide high, positive contact pressure and longer contact life.
IAGN/IUGN
The IAGN/IUGN series meets the requirements of MIL-PRF-555629
The IAGN/IUGN family is a sealed toggle version of the IAG/IUG family. The silicone rubber seal around the handle assures panel seal integrity and makes this style a natural for harsh environments.
This sealed toggle family: 
- is available in one to three poles with ratings of .050 to 100 amperes.
- The IUGN series is an "A" frame breaker up to 50 amps.
- The IULN series is a "C" frame breaker up to 100 amps.
More information about the IAGN/IUGN series >>
Carling and Airpax
We stock several lines of Carling and Airpax magnetic circuit breakers. More information about the Airpax series >>
Carling standard breaker colors are black with black toggles, medium delay curve for both AC and DC circuits and buss lugs with 10-32 screws. Special orders and colors are available.
| Breaker | Description | Available Amps |
|---|---|---|
| AA-1 |  The standard marine breaker for protection of circuits up to 50 amps. |
5, 10, 15, 20, 25, 30, 40, 50 |
| AA-2 |  Same breaker as AA-1 with two poles. Each pole has a separate toggle with a connecting bar to tie the toggles together. |
5, 10, 15, 25, 30, 40 |
| AA-3 |  Same as above with three poles. Each pole has a separate toggle with a connecting bar to tie all three together. |
30, 50 |
| AB-2 | A two pole breaker with the same features as above except with a single toggle which controls both poles. This feature makes installation much easier since there is no need to add or remove the connector bar between the two toggles. | 5, 10, 15, 20, 25, 30, 40, 50 |
| AD-1 | A single pole breaker with a roker actuator instead of a toggle. Designed to be mounted horizontally, the breaker is available in a wide variety of markings and colors. | 5, 10, 15, 20, 25, 30, 40, 50 |
| AD-2 | A two pole version of the AD-1 breaker | 5, 10, 15, 20, 25, 30, 40, 50 |
| CA-1 | A medium frame single pole breaker with values up to 100 amps. We stock breakers with a toggle actuator and a 10-32 stud in values up to 50 amps, and in values from 60 amps – 100 amps with a 1/4" – 20 stud. | 5, 10, 15, 20, 25, 30, 40, 50, 60, 70, 80, 100 |
| CA-2 | A two pole version of the CA-1 breaker | 5, 10, 15, 20, 25, 30, 40, 50, 60, 70, 80, 100 |
| CA-3 | A three pole version of the CA-1 breaker | 30, 50, 100 |
| CA-4 | A four pole version of the CA-1 breaker | 50, 100 |