OCPD is an acronym commonly used in building codes for OverCurrent Protective Device. Circuit breakers and fuses are both an OCPD. They protect against too much current flowing through the wiring in a house, which can easily heat them to the point that they ignite nearby flammable materialsa common cause of house fires. 

    The National Electrical Code (NEC) divides OCPD’s into two categories:
•• Branch-Circuit OCPD - "A device capable of providing protection for service, feeder, and branch circuits and equipment."
•• Supplementary OCPD - "A device intended to provide limited overcurrent protection for specific applications and utilization equipment such as luminaires and appliances. This limited protection is in addition to the protection provided in the branch circuit by the branch-circuit overcurrent protective device."

    The first OCPD’s were fuses, which depended on the known melting point of a metal strip (viewable in the window of the old screw-in type fuses) to trip the circuit when excessive current overheated it. Fuses are very reliable, but are single-use and must be replaced after each overcurrent episode. Also, early fuses could be switched-out for one with a higher amperage rating than was safe for the wiring; which often happened when a homeowner got aggravated with repeatedly replacing blown fuses. Circuit breakers are mechanical devices that can be easily reset and they gradually replaced fuses for most applications in the mid-20th century.

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Here’s a selection of some of our other articles about OCPD's:

• What is the maximum number of circuit breakers allowed in an electric panel?

• When did circuit breakers replace fuses in homes? 

• Can you add circuit breakers by different manufacturers to an electric panel if they fit?

• My circuit breaker won't reset. What's wrong? 

• What causes a hot circuit breaker in an electrical panel? 

• What temperature is too hot for a circuit breaker?

• What does maximum sum of breaker ratings per stab mean in an electrical panel?

• What is the life expectancy of a circuit breaker? 

• What is a tandem circuit breaker? 

• What is a double tap at a circuit breaker? 

• What is the difference between a Combination Arc Fault Circuit Interrupter (CAFCI) and an Arc Fault Circuit Interrupter (AFCI) circuit breaker?   

• What does it mean when a wire is "overstripped" at a circuit breaker?

• What is the maximum allowed height of a circuit breaker (OCPD) above the floor?

• Why is there no main shut-off breaker in my electric panel?

•  Can an unused (spare) circuit breaker remain in an electrical panel or does it have to be removed?