Inspection Detail

Inspection: 312676588 - Chula Vista Electric

Inspection Information - Office: San Diego District Office

Investigation Summary

On December 28, 2007, an electrical outage was affecting a portion of the building. Employee #1 and Employee #2 of Chula Vista Electric responded to the site to troubleshoot and repair the equipment causing the electrical outage. A worker led Employee #1 and #2 to an electrical room, where Employee #1 opened the 4,160-volt 3-phase OFC switch device. The OFC switching device contains three separate OFC switches, one switch for each electrical phase. The OFC device had a mechanical linkage that turns the internal fuses approximately a .25 turn. The turning of the fuse .25 turn disconnects the fuses from their contact points within the switch. The fuses are immersed in clear dielectric oil, which is intended to quench any electrical arc that may occur when the fuses are connected or disconnected from an energized electrical source. The three OFC switches are opened and closed simultaneously through the use of the mechanical linkage. Electrical power was still energized to the incoming (line) side of the fuse contact point within the OFC switches. Opening the OFC switch device deenergized the electrical power to the OFC fuses and to a malfunctioning transformer powered by the OFC switch device. As part of the troubleshooting process Employee #1 checked the fuses in the OFC switches. One fuse holder was removed completely and visually inspected. Employee #1 saw that the fuse was blown and noted that the dielectric oil within the switch was dark in color. Employee #1 placed the fuse holder on the floor and then raised the other two fuse holders and supported them on the fuse holder's alignment dowels that were located on the side of the fuse holder, partially suspending the fuse holder in the OFC switch. Employee #1 then assisted Employee #2 in inspecting the malfunctioning transformer unit. After assisting Employee #2 in the inspection of the transformer, Employee #1 returned to inspect the remaining two fuses in the OFC switches. To inspect the fuses Employee #1 had partially removed the fuse holder slightly from their suspended positions in the OFC switch. Employee #1 looked at the fuse to determine if the fuse was blown. Employee #1 then lowered the fuse holder back into the OFC switch suspending the fuse holders on the alignment dowel pins. After completing the inspection of the fuses, Employee #1 slightly rotated one of the fuse holders so that it would be better supported. Immediately after Employee #1 pulled his hand from the fuse holder he heard a "pop" sound. At that time an arc flash occurred within the OFC switch. This arc flash caused intense radiant heat and a short lived fire which expanded out of the OFC switch into the electrical room burning Employee #1 Employee #2 and the coworker who led them into the room. Employee #1 and #2 were hospitalized and suffered from unspecified burns as a result of the event.

Keywords: BURN, ELECTRIC ARC, ELECTRICAL VAULT, ELECTRICAL TESTING, ELECTRICIAN, ELECTRICAL WORK, ELECTRICAL FAULT