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Adjustable trip Protections

Question asked by mia.marvelli on Oct 8, 2018

An EE who is engr on staff with one of the Calif subtrades firms sent this info to us, pointing out what he sees as a potential danger with the new adjustable breaker types.  The question becomes, "is there anything related to 240.6 that secures tampering resistance to an acceptable/confident level?" "Does bolting down, or locked access really provide appropriate level of security?" "Should NEC address this differently?"

His text:

Within the last several days ran across a different problem with Square D in particular.  We had a submittal stating “1200AS/1000AT” for a PG Power pack circuit breaker.  I rely on SKM software for setting circuit breakers and then arc-flash labels.   The series of circuit breakers uses Micrologic electronic trip units, which have existed for a long time.  The difference this time is that Square D did not provide a 1000A trip so that the maximum setting is 1000A,  but a type ‘C’ micrologic trip.  In the submittal they did not identify the trip type and we had to field verify.  To get the 1000A trip, for ‘C’,  I had to set it for .83  (.83 x 1200A = 996A).   This means that it can at any time be changed back to a setting of 1 or 1200A.  I have asked our crew to install ‘seals’ on the small plastic door as a notification not to adjust.   Beyond the obvious protection levels, we now provide safety arc-flash labels that are based on a calculation that includes the circuit breaker settings.  Should someone unknowingly change the setting, it creates a problem.  This situation occurs with most manufacturers where electronic trip devices are used. The present code allows for the seal, but also allows an enclosure door or restricted room access.  This does not identify a specific circuit breaker that has a required reduced setting. 



CEC article 240.6 (C ) states: 

Restricted Access Adjustable-Trip Circuit Breakers.  A circuit breaker(s) that has restricted to access the adjusting means shall be permitted to have an ampere ratings (s) that is equal to the adjusted current setting (long-time pickup setting).  Restricted access shall be defines as located behing one of the following:  (1) Removable and sealable covers over the adjusting means. (2) Bolted equipment enclosure doors, (3) Locked doors accessible only to qualified personnel


Recommendation:   Repeal:  " (2)  Bolted equipment enclosure doors, (3) Locked doors accessible only to qualified personnel."