Eaton Logo

Eaton’s recommendation for periodic exercise and field test for MCCB ?

Eaton’s recommendation is to periodically exercise and field test molded case circuit breakers per guidance found in NEMA document AB 4.  The period between (preventive maintenance) field testing cycles is to be determined by the customer/owner; typical periods are 6 month or one year intervals.

NEMA AB 4 is titled “Guidelines for Inspection and Preventive Maintenance of Molded Case Circuit Breakers Used in Commercial and Industrial Applications.”  NEMA AB 4 contains one mechanical test and five electrical tests.

The five electrical tests provide expected pass/fail criteria, except for the Individual Pole Resistance Test (Millivolt Drop).  The mV drop test recommends contacting the circuit breaker manufacturer for acceptable test results.  For Eaton molded case circuit breakers tested per the NEMA AB 4 mV drop test, a mV drop reading of 200mV, or less, is considered acceptable.  Any mV drop reading in excess of 200mV is cause for review of that circuit breaker’s suitability for continued use in the field.  Additionally the Rated Hold-In Test is typically performed only in cases where the breaker was noted, prior to testing, to have been nuisance tripping under normal operating conditions for no identifiable reason.

A free copy of NEMA AB 4 is available from NEMA’s web site at; type “ab4” in the Search field at the top of the page, hit the keyboard Enter key, and follow instructions that appear for downloading the document.  Note that email registration is required in order to obtain the document.