Circuit Breaker Handle Locking Mechanism for Safety
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Solution Overview
Problem
Two-pole residential circuit breakers lack a mechanism to prevent the main contacts from closing in situations where a fault condition is not detected or if a fault condition is present when the circuit breaker is turned to the fully ON position, posing a safety hazard.
Innovation Solution
A locking mechanism comprising a locking handle shaft and a locking latch that blocks and unblocks the breaker handle, keeping it in a mid-position until a self-test is passed, preventing the main contacts from closing until the test is completed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a locking mechanism is added to prevent main contacts from closing during fault conditions, then safety is improved, but device complexity increases
Solution Approach 1:
The locking mechanism performs a self-test operation before allowing the breaker handle to be turned to the fully ON position. The locking shaft engages with the locking latch to prevent rotation until the self-test confirms no fault conditions exist, thereby preventing dangerous situations where fault conditions might be present
Solution Approach 2:
The locking shaft acts as an intermediary mechanical component between the breaker handle and the main contacts. It translates the passage of self-test into mechanical permission by rotating to unblock the breaker handle, thereby mediating the transition from blocked to unblocked state based on test results
2Reliability
If the breaker handle is blocked until self-test is passed, then fault detection reliability is improved, but ease of operation deteriorates
Solution Approach 1:
The system automatically performs the self-test operation before allowing normal operation. The locking mechanism is designed to automatically engage or disengage based on the self-test result, eliminating the need for manual intervention and maintaining ease of operation while ensuring safety
Solution Approach 2:
The locking mechanism is self-actuating based on the self-test result. When the self-test passes, the locking shaft automatically rotates to unblock the breaker handle without requiring manual operation, making the system serve itself and maintain ease of operation
Data Source
AI summary
An apparatus and a method are provided to block and unblock a breaker handle of a circuit breaker having main contacts. The apparatus comprises a locking mechanism including a locking handle shaft and a locking latch. The locking handle shaft is configured to latch the locking mechanism for keeping the breaker handle in a mid-position in which the main contacts stay open. The locking handle shaft has a latching surface configured to be removed from its position in order to rotate the breaker handle to a fully ON position in which the main contacts fully close. The locking latch is configured to prevent rotation of the locking handle shaft. The locking latch is configured to engage and disengage with the locking handle shaft in order to rotate the breaker handle from a reset position to the mid-position in which the locking mechanism locks the breaker handle rotation thus preventing the main contacts from closing. The breaker handle is stopped at the mid-position by the locking mechanism until a self-test is passed.