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What is an electrical OCPD?
Sunday, April 17, 2022
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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