Facilities Management -Operations and Maintenance FM/O&M/QA/RCA/XXX Root Cause Analysis Report 29.07.15 Subject: TRIP ON LV PANEL MDB-N DUE TO SMALL SIZE ACB FRAME (800-2000A) Brief Description: Operation reported a trip on fire pump during weekly test run this morning @ 3:20am 28/7/15. Upon start, there was a trip affecting the power supply on LV panel (MDB-N). LV panel (MDB-N) is located at the east staff car park utility building. Checks found 2500A Eaton ACB (incomer) was tripped and 2500A ACB for fire pump was also tripped, in which both ACB are located on same LV panel (MDB-N). Analysis: Subject Description / Details Remarks Background of LV panel There at 3nos of ACB (Eaton make) on the LV panel, 2500 ACB (incomer) 3P, Fire pump ACB 2000A 3P and DG ACB 2500 4P. LV panel (MDB-N) is located at the east staff car park utility building. Contractor whom has installed the ACB is unknown. Findings/ Analysis Tripping of the Fire pump upon start was reported during the weekly test run carried out on 28-07-2015 at 03:20 hrs. The pump is powered thru’ LV supply from MDB-N located at east staff car park. The tripping occurred when the motor was running on star. Found that Main Incomer ACB (Instantaneous trip) also tripped on the same fault as Fire Pump ACB (Instantaneous fault). The settings of the Main Incomer ACB and the Fire Pump ACB are same (Lds-1, ldt-2s, sds-2, sdt-0.1, Inst-2). On further checks on the Fire Pump ACB, it is found that the frame size of the chasis was smaller, with CAT# EN203HADNSNNNWC having small contact thickness (for max. rating upto 2000A). Whereas the Fire Pump Incomer ACB is 2500A and suitable frame size for the chasis is CAT# EN324HADNSNNNWC rated (2500-3200A), having contacts more than twice in thickness. We have observed carbon residue around the ACB and when racked out, and flashed melted copper due to the arc was found around the frame blade.