S Sentron Molded Case

S Sentron Molded Case Circuit Breakers

Section 2.15.1.0 Page 57 Prepared by Ray Clark , Senior Application Engineer September, 2003 Standard Ampacity Settings With Applications Notes & Data Electronic Trip Circuit Breakers

The available trip settings of various There are two main application issues Paragraph (c) specifically says that "Sensitrip" trip units sometimes do here. the rating is permitted to be "…equal not exactly match the ampacity to the adjusted current setting (long- ratings of standard thermal magnetic First, in looking at the tables in time pickup setting)." Subject to the circuit breakers. For example the section 310 the given cable conditions in 240-6(c) for restricted 250A rating cannot be set on any of ampacities do not exactly match the access. This means that it would be our Sensitrip electronic trip circuit standard thermal magnetic breaker allowable to adjust the trip unit long- breakers, the closest setting is either ratings given in 240-6(a), such as time pickup setting to the next rating 240A or 260A. Questions have been 250A. In fact I could not find 250A above the de-rated cable ampacity, if raised regarding the acceptability of in any table as a given ampacity for below 800A, or, to choose a setting these settings. . any cable size. Further, even if there less than or equal to the cable The only potential reason to question were an exact 250A ampacity shown ampacity if above 800A, in breaker ratings is the requirement in for a specific cable size, the various accordance with 240-3(b). The exact the NEC that electrical circuits be de-rating factor for temperature, setting, or "rating", value on the protected by overcurrent protective conduit fill, etc., can significantly adjustable trip unit is not dictated by devices, either fuses or circuit reduce the ampacity. The result is the code. Further, the term breakers, that are sized appropriately. that the matching of the overcurrent "standard" in the phrase "next higher Article 210-20 requires overcurrent device to the cable ampacity will not standard overcurrent device rating" protection for branch circuit usually mean that an exact ampacity can be interpreted to mean the next conductors and 230-90 requires such as "250" would be required in available setting on that particular overcurrent protection for service an overcurrent protective device to circuit breaker. conductors, both refer to 240-3 and meet the code. 240-6 for the ratings of the required Due to the typical interval between protective devices. Secondly, section 240-6 lists long-time pickup settings on an "Standard Ampere Ratings" for electronic trip breaker, in many Article 240-3 addresses general overcurrent protective devices. 240- cases, the next higher setting on an protection of conductors, specifying 6(a), "Fuses and Fixed-Trip Circuit 800A or smaller breaker will be that conductors be ".. protected Breakers", shows various ratings lower than the next higher rating of against overcurrent in accordance from 15 to 6000A, including our the standard fixed-trip breaker. For with their ampacities as specified in example 250A. This is the list that is example, if the cable ampacity where section 310-15, unless otherwise generally referred to as the to be 258A, the code allowed next permitted …" and goes on to list "standard" ratings. However, the higher fixed-trip breaker rating several exceptions. One of these Sensitrip circuit breakers are not would be 300A, in the case of the exceptions (240-3(b)) allows for "fixed" they are adjustable trip circuit Sensitrip the next setting would be selecting the "next higher standard breakers. Further, right after the 260A. The 260A setting would overcurrent device rating" if the listings of the "standard" fixed obviously provide better protection. ampacity is below 800A. Above breaker ratings is a statement that Although this is one of the "best 800A the ampacity of the conductors "The use of fuses and inverse time case" examples, the typical amp must be "equal to or greater than the circuit breakers with nonstandard difference between trip settings on an rating of the overcurrent device as ampere ratings shall be permitted." electronic trip breaker is less than the defined in Section 240-6." Both of typical difference between fixed-trip these statements allow some The next two paragraphs 240-6(b) ratings of thermal magnetic breakers flexibility in sizing the overcurrent and (c) specifically address resulting in equal or better protection. protective device to the ampere rating "Adjustable-Trip Circuit Breakers", of the conductors. which would include the Sensitrip breakers. In these paragraphs there are no specific ampacities shown.