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November 18, 2009
SAE Circuit Breaker Testing


Automotive circuit breakers such as the OptiFuse ACB or Bussmann Shortstop® are generally not tested by UL or CSA.  These type of circuit breakers are low voltage devices (12 or 24 VDC) and are covered under standards developed by SAE (formerly known as the Society of Automotive Engineers) rather than standards set created UL or CSA.

ACB-N Automtive Circuit Breakers

The interesting thing about SAE as opposed to UL and/or CSA is that SAE is a non-profit professional organization rather than a "for profit" corporation.  Additionally SAE does not actually do any testing themselves but just sets the standards associated with the manufacturing of vehicles.  Testing is performed by outside testing labs or by the manufacturers themselves.

Over the years, SAE has developed a standard for automotive circuit breakers.  This standard is known as SAE J553.

In the standard, one will find the prescribed test set-up and the criteria needed in order for a circuit breaker to meet in order to satisfy the standard’s requirements.

The test set up consists of a regulated DC power supply, connected to a test load (usually high-power low impedance resistors) through wires of specific AWG wire gauges all in series with the circuit breaker to be tested.

Certain ambient requirements need to be maintained during the tests (such as a temperature of 23° C +/- 3° and a relative humidity between 45% and 75%).

Once the set up is complete, then the circuit breakers are subjected to a variety of tests that measure voltage drop, time needed to open the circuit breaker at certain currents, interrupting capabilities and cycling capabilities.

The voltage drop test is dependent upon the amperage and voltage rating of the breaker under test and changes from size to size.

The current test consists of two test points that each circuit breaker must meet:

  1. At 135% of the circuit breaker rating, the breaker must open up before 30 minutes
  2. At 200% of the circuit breaker rating, the breaker must open up before 60 seconds
These two current tests are the only tests required by an automotive circuit breaker.  Between these two tests a minimum time of 30 minutes must pass so the circuit breaker can cool back down to "room temperature"

The current limitation testing is the ability of the circuit breaker to limit the amount of current in the circuit below that of what the circuit would see if no circuit breaker was present in the first place.  The interrupting test criteria is specific to the particular current rating of the circuit breaker.

After the current limitation test, an endurance test is completed.  The endurance test is designed to verify that the circuit breaker can operate more than just one time before failing.

In addition to the current limitation and endurance tests above, the circuit breakers are also subjected to an "interrupt test".  The interrupt test is performed to measure the circuit breaker’s ability to safely open higher currents.  The current level is particular to the normal current rating of the circuit breaker.

In summary, each automotive circuit breaker is tested in accordance to SAE J553.  The required tests include:
  • Voltage drop test
  • Overload test at 135% and 200%
  • Effective current limitation test
  • Endurance test
  • Interrupting test
In addition to the required tests, some optional tests can be made including:
  • Temperature tests - for extended temperatures
  • Humidity tests - for extended humidity
  • Salt / Fog tests
  • Immersion & Splash test
  • Drop test
  • Environmental Extremes test
OptiFuse is serious about providing our customers with quality products.  All of the required tests are preformed at our Taiwan factory on each manufacturing lot.  Additionally, these tests are also performed at the OptiFuse headquarters location in California with lot test data available upon demand.

Thank you very much for your continued support of OptiFuse as we demonstrate our commitment to providing quality products.

Jim Kalb


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