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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.
Remove the dust and dirt that have accumulated on the circuit breaker surface and
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
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.

CTA-ID : 9161
FA93199  |  14-Jan-2011  | Maintenance
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