Situation: 2000A ATS (480V, 4-pole, contactor based bypass Isolation type) is fed from 2000A LVPCB. ATS’s UL 1008 Withstand and Close On Rating (WCR) is 100KA but STD rating is only 36KA for 18-cycle.
In order to achieve selectivity with a downstream CB, STD was imposed on the 2000A LVPCB. The issue is ATS did not have a high enough STD rating. STD is less than 18-cycle, so ATS's duty-cycle is OK, though.
A proposed solution was to add a current limiting fuse before the ATS and reduce the fault current. I think this is a so called “Up-Over-and Down” method?
So, my questions are
1. Does this seem right?
2. I know “Up-Over-and-Down” method can be used on a passive device. Is the ATS a truly passive device?
3. Any other ways to resolve this issue?
In order to achieve selectivity with a downstream CB, STD was imposed on the 2000A LVPCB. The issue is ATS did not have a high enough STD rating. STD is less than 18-cycle, so ATS's duty-cycle is OK, though.
A proposed solution was to add a current limiting fuse before the ATS and reduce the fault current. I think this is a so called “Up-Over-and Down” method?
So, my questions are
1. Does this seem right?
2. I know “Up-Over-and-Down” method can be used on a passive device. Is the ATS a truly passive device?
3. Any other ways to resolve this issue?