What are the routine maintenance guidelines for Merlin Gerin circuit breakers?
Recommended inspection intervals Merlin Gerin circuit breakers are designed to be maintenance-free. However, all equipment with moving parts requires periodic inspection to ensure optimum performance and reliability. It is recommended that the circuit breakers be routinely inspected six months after installation, followed by annual inspection. Intervals can vary depending on particular usages and environments. Inspection of terminals Connections to circuit breaker terminals should be inspected. If there is discoloration due to overheating, the connections should be disassembled and the surface cleaned before reinstallation. It is essential that electrical connections be made carefully in order to prevent overheating; Check for terminal tightness. Cleaning Remove the dust and dirt that have accumulated on the circuit breaker surface and terminals. Mechanical checks Even over long periods of time, circuit breakers are not often required to operate on overload or short-circuit conditions. Therefore it is essential to operate the circuit breaker periodically. To trip the circuit breaker, push the push-to-trip button. Insulation resistance tests When a circuit breaker is subjected to severe operating conditions, an insulation resistance test should be performed as indicated in NEMA standard publication No. AB4-1996. An insulation resistance test is used to determine the quality of the insulation between phases and phase-to-ground. The resistance test is made with a dc voltage higher than the rated voltage to determine the actual resistance of the insulation. The most common testing method employs a ``megger`` type instrument. A 1000 V instrument will provide a more reliable test because it is capable of detecting tracking on insulated surfaces. Resistance values below one megohm are unsafe and should be investigated. An insulation test should be made: Between line and load terminals of individual poles with the circuit breaker contacts open; Between adjacent poles and from poles to the metallic supporting structure with the circuit breaker contacts closed. The latter test may be done with the circuit breaker in place after the line and load conductors have been removed, or with the circuit breaker bolted to a metallic base which simulates the in-service mounting. Electrical tests These tests require equipment for conducting pole resistance, overcurrent and instantaneous tripping, in accordance with NEMA Standard publication No. AB4. They are not within the scope of normal field operation.