Inspection Detail

Inspection: 311863708 - First Solar, Inc.

Inspection Information - Office: Sacramento District Office

Investigation Summary

On July 23, 2008, Employee #1 was working for a company who supplies solar equipment. The solar equipment had to be converted from DC to AC. To accomplish the conversion, 440-550 volt DC power from the solar panels entered an inverter, which was housed in a locked inverter cabinet. The inverter transferred the power to a transformer that was wired in a Wye configuration with a center tap that produced 277 volts between ground and one phase and 480 volts between phases. Three exposed, energized bus bars were located at the bottom of the left side of the cabinet. The DC disconnect automatically shut off DC power from the solar panels when the cabinet door was unlocked and opened but the AC power continued to be present since it received feedback from the power lines to which it was connected. The AC lines between the cabinet and the system had two separate disconnecting means, one on the pole and one in the cabinet. The disconnect on the pole was a fuse that required a lineman. As the electrician left the jobsite, at approximately 5:15 p.m., he noticed Employee #1 entering the jobsite but he was not flagged down to help deenergize the cabinet. Employee #1 did not have a key for the cabinet so he used needle-nose pliers to open it, which automatically shut down the DC coming into the inverter cabinet. However, the AC bus bars were still energized. Employee #1 intended to attach monitoring equipment to the system and began to loosen a nut on one of the energized bus bars with a uninsulated crescent wrench. The wrench made contact with a second energized bus bar in contact with the first. The 480-volt short circuit caused an arc flash. Employee #1 was hospitalized with multiple burns.

Keywords: SHOCK, LOCKOUT, ELECTRIC SHOCK, HAND TOOL