In looking at the latest edition [7th] of UL 1008 for transfer switches I came across the following:
“The circuit breaker must include an instantaneous trip response and shall not include a sort time trip response” as it relates to switches tested per 9.13.3.10 & 9.1.2.3.
It seems different manufactures have different interpretations. So does this disqualify any breaker with an adjustable STPU / STD setting from protecting a 3-cycle [0.05sec] any breaker rated switch, even if the breaker has an instantaneous override less than the interrupting kA of the switch? It seems counterproductive because if I have a LSI MCCB I can almost always provide better protection in the instantaneous and in the short time than with a standard thermal mag. C/B. For low level arcing / fault currents, that sometimes extend into the LTD portion of the T/M I can adjust the STD down to pick up these currents faster providing better equipment and personal protection? One manufacture I talked to indicated that if the breaker has an adjustable short time ahead of the switch the switch is misapplied, even though the TCC’s show different? Then what about the specific breaker ratings, many breakers on the “Specific Breaker” list can be provided with a myriad of trip units types and styles from your standard TM, to LI, LSI, LSIG. So does this restrict the specific breaker to the T/M? The literature does not differentiate. Just curious if anyone else has run into this and other thought and opinions… READ MORE.
