Narrative:

I was beginning to remove the R-134A air conditioning unit from the aft equipment area of [aircraft] to prepare for a flight control cable inspection. We had several jobs at the time by other technicians. I was following the procedure from CE560 MM 21-52-00 says to disconnect battery and external power. I knew other techs were using power so I decided to prepare the air conditioner pallet for removal and leave the power disconnection for last. As I was loosing the mount bolts of the pallet (the forward left mount bolt is closest to the power relay) my socket had slipped off the bolt and made contact with the power relay positive terminal. This caused some arcing between the positive terminal and the pallet frame. Once power was secured and I was able to fully remove the air conditioning pallet I did find that both the ground and power terminal boots were torn. Also the power terminal boot was not installed correctly. The boot was rolled back from the terminal end exposing the connection.most obvious suggestion is to follow MM procedures. The air conditioning pallet should be planned to be removed during a scheduled power off situation during the inspection. Once I had the pallet removed from the aircraft I could fully see where the arcing occurred. As I mentioned above the power terminal boot was not installed correctly. This however would not make a difference in my situation. The design of the power relay is such that both the power and ground terminals are exposed even with the boot properly installed. The concern that I have is that if a technician would be in the aft equipment area working on another system with power on they could easily drop a tool and make contact with the power relay of the air conditioning pallet.

Related reports:

Google
 

Original NASA ASRS Text

Title: An Aircraft Maintenance Technician (AMT) reports that protective boots currently installed over the R-134A Air Conditioning Unit Relay 'Positive' and 'Ground' terminal end studs are not adequate to protect technicians and tools from exposure to electrical power. The Air Conditioning Unit is mounted on the forward side of the aft equipment area of Cessna-560 aircraft.

Narrative: I was beginning to remove the R-134A Air Conditioning Unit from the aft equipment area of [aircraft] to prepare for a flight control cable inspection. We had several jobs at the time by other technicians. I was following the procedure from CE560 MM 21-52-00 says to disconnect battery and external power. I knew other techs were using power so I decided to prepare the air conditioner pallet for removal and leave the power disconnection for last. As I was loosing the mount bolts of the pallet (the forward left mount bolt is closest to the power relay) my socket had slipped off the bolt and made contact with the power relay positive terminal. This caused some arcing between the positive terminal and the pallet frame. Once power was secured and I was able to fully remove the air conditioning pallet I did find that both the ground and power terminal boots were torn. Also the power terminal boot was not installed correctly. The boot was rolled back from the terminal end exposing the connection.Most obvious suggestion is to follow MM procedures. The air conditioning pallet should be planned to be removed during a scheduled power off situation during the inspection. Once I had the pallet removed from the aircraft I could fully see where the arcing occurred. As I mentioned above the power terminal boot was not installed correctly. This however would not make a difference in my situation. The design of the power relay is such that both the power and ground terminals are exposed even with the boot properly installed. The concern that I have is that if a technician would be in the aft equipment area working on another system with power on they could easily drop a tool and make contact with the power relay of the air conditioning pallet.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.