EMB ERJ 170/175 ER/LR
Maintenance Airframe; Maintenance Powerplant
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Maintenance; Deviation / Discrepancy - Procedural Published Material / Policy; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Aircraft Aircraft Damaged; General Maintenance Action
Procedure; Manuals; Aircraft
While performing Removal of MAU (Module Avionics Unit) 2; The first step is to remove the EICC (Emergency Integrated Control Center). The first step in removal of the EICC is to de-energize HOT BUS 1. I performed the procedure of removing battery 1 connector; removing external power and tagging the overhead panel. Ground power cord was removed; and external power door shut and tagged. I removed the rain cover and connectors to the EICC. I was in the process of removing the power and ground feed cables to the EICC at the back of the unit. I backed the ground wire nut most of the way off and started on the battery 1 wire. While removing the nut from the battery 1 cable my ratchet hit the aileron bell crank and an electrical arc occurred. The arc was massive. I than noticed glowing coming from the aileron cable force cables. I ran to the cockpit and removed the fire extinguisher. When I returned to the fwd electronics bay area; the cables were still glowing. I discharged the extinguisher onto the force cables. One quick burst on the captain's side and one quick burst on the co pilots' side. Verifying no more glow; I had co workers go get the lead and sup. I was working off my IPAD.
Technician reported failing to disconnect #2 Main Battery during maintenance; causing an electrical arc and a fire.