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June 9, 2009
What is your Type?...

Have you ever noticed that AUTOMOTIVE circuit breakers are available in distinct types?  There are type I, II and III breakers to choose from (this "type" designation comes directly from SAE and their specification J553). 

Automotive CBs

Here’s the lowdown on each type so you can use or recommend the proper one for the right application:

TYPE I   <=click to get more information from the OptiFuse website

The Type I automotive circuit breaker is also known as an auto-reset type breaker.  This type of circuit breaker uses a "bi-metal" strip that heats up, flexes and opens the circuit when an overload situation occurs.  Once the circuit breaker disconnects the circuit,, the "bi-metal" strip eventually cools down, unflexes and reconnects the circuit.  If the original overload problem is not fixed before the circuit breaker resets, then the "bi-metal" strip will reheat and the process of connecting and unconnecting starts all over again.

This condition is sometimes called a "bounce" effect...(the breaker continuing to open and close indefinitely).  Eventually, the "bounce" could cause a premature failure in the circuit breaker and/or circuit itself.

TYPE II  <=click to get more information from the OptiFuse website

The Type II circuit breaker is sometimes known as a "modified" circuit breaker.  The basic construction of the type II breaker is same as the type I breaker except that a heating element is placed on or around the bimetal strip. 

The way this works is that the heating element is OFF (cold) when the circuit breaker is closed (normal condition) but when the circuit breaker opens, the heating element is turned ON adding heat to the circuit breaker’s bi-metal strip.  This way the bi-metal strip NEVER has a chance to cool off and reset itself.  This action keeps the breaker from "bouncing" off and on. 

The only way to reset the type II circuit breaker is to turn off the power to the entire system (generally this means turning off the ignition switch for a few moments).

TYPE III  <=click to get more information from the OptiFuse website

The Type III circuit breaker is also known as a "manual reset" circuit breaker.  Once again, the basic structure is the same as the other two breakers mentioned above except that there is a mechanical latch that is activated when the circuit breaker opens.  This latch much be reset before the circuit breaker can reset itself.  Because the type III circuit breaker must be manually reset, the breaker must be located in an accessible place.  

I hope that this primer helps answer the "type" of questions that are on your mind... 

One side note...I appreciate all the positive feedback I’ve received so far regarding this blog...I’ll try to keep it fresh, educational and easy to read....

Thanks for all you continued support of OptiFuse. 

Jim Kalb


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