Fuses, Fusible Links & Circuit Breakers

Component Related Documentation

Devices such as fuses, fusible links and circuit breakers are placed in series in circuits to protect the circuits from damage caused by overloads or short circuits. OCPD, an acronym meaning “over-current protection device” is a term sometimes used to for these devices.

Fuses and fusible links have sections which carry current up to a specified amperage, but which will overheat and melt when the current density becomes too great, thus stopping the flow of current before other devices and wiring in the circuit can be damaged. To restore operation of the circuit, the fuse or fusible link must be replaced.

Circuit breakers are automatically operated electrical switches which disconnect current flow. Unlike a fuse or fusible link which operates once and then must be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation. The construction and operation of a circuit breaker varies with its voltage and amperage rating.

Before replacing a fuse or fusible link, or resetting a circuit breaker, inspect the circuit for the cause of the failure. Never circumvent circuit protection by installing a fuse, fisible link or circuit breaker with one of a higher amperage rating.

Safety Related Notes

Before working on this machine, perform lockout-tagout procedures per the rules of your plant. Determine the sources of energy on this machine – electrical, pneumatic and hydraulic – and release or vent sources of stored energy – electrical capacitors, air receivers, and hydraulic accumulators. Shut off sources of power – electrical, pneumatic and hydraulic. Safely block mechanical sources of energy such as loaded springs and loaded machine members, or safely position the machine members so they are unloaded and springs are not under tension. Beware of hot hydraulic fluid and hot surfaces which can cause burns. Never “crack a hydraulic or pneumatic fitting” to check for the presence of stored energy. Hydraulic fluid injection injuries, as well as injection injuries from many other fluids, are extremely serious and must be treated immediately by medical personnel familiar with this type of injury. Loss of body parts or death may result from improperly treated fluid injection injuries! Never use your hands to feel for a hydraulic leak! Never use compressed air to blow dust off yourself or someone else – there is risk of an air injection injury. Review the schematics and think before proceeding to work on the machine to ensure you have made the machine safe to work on.