Date: 201209
Local time of day: 0001-0600
Location: ZZZ.Airport, US
Light: Night
Aircraft: EMB ERJ 170/175 ER/LR
Operator: Air Carrier
Operating under: Part 121
Flight phase: Parked
Reporter organization: Air Carrier
Reporter function: Technician
Reporter qualification: Maintenance Airframe; Maintenance Powerplant
Human factors: Communication Breakdown; Situational Awareness
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural FAR; Deviation / Discrepancy - Procedural Maintenance; Ground Event / Encounter Other / Unknown
Detector: Person Maintenance
When detected: Other During Maintenance
Result: General Maintenance Action
Contributing factors: Equipment / Tooling; Human Factors; Company Policy; Environment - Non Weather Related
Primary problem: Equipment / Tooling

Narrative: In our Routine Overnight Hangar we are repeatedly being electrically shocked by the aircraft while performing nightly maintenance. This has only been an issue this year. This has been repeatedly brought to Management's attention and we have been told that licensed electricians have been brought in when available at their convenience to look at the problem and [that] there is none. What is happening when the aircraft comes to the hangar for nightly maintenance. We need to hook-up a ground power [electrical] cart to supply electrical power to the aircraft. The ground power cart is hooked-up to the electrical drop located at the north end on the hangar. It is a dual hook-up cart (can supply power to two aircraft at one time). We were told that the reason we are getting shocked is because the aircraft is not grounded to the hangar floor. When an aircraft is grounded; it is to make the aircraft and what it is grounded to; electrically the same. I was personally getting shocked when hooking up the aircraft to ground. I took out my Volt Meter and found we are passing Alternating Current (AC) volts and amps from the aircraft to the hangar floor ground [connection]. This should not happen. The power cart should be supplying the electrical ground back to the power source. This is dangerous because somewhere we are not providing a way for the power cart to return all the voltage back to the power source ground and it is building up on the aircraft. [The] poor hangar wiring has been brought to Management numerous times as stated and we have been told that licensed electrical technicians have been into check out the hangar and power cart and are not able to find any significant findings. We have also been told that the licensed electrical technician believes that it is because it has been so dry and the dirt around the building grounding rod is dry; not allowing all the power to return to ground. Obviously it is still a problem even after the electricians have checked out the power source. It is a dangerous situation every night. It does not happen every night. The wiring needs to be thoroughly gone over. It is getting to the point that we do not want to work on the aircraft because we are getting shocked.

Callback: Reporter stated that for many months there have been multiple incidents of mechanics being electrically shocked when they would connect the portable Hobart ground power cart electrical cord to their ERJ-170 aircraft. He had another Mechanic take a video of the electrical spark jumping from the aircraft grounding lug to the grounding cable as he connected the cable to the aircraft. He did that to emphasize to Management the seriousness of the situation on the hangar floor. Every night they have open fuel cells (tanks) on their aircraft; including those connected to the same unsafe power cart. He and other mechanics isolated the problem to the same power cart after using a different power source for the same aircraft and not getting electrically shocked. His company finally took the power cart out of service; but has not repaired the unit.



Synopsis: An Aircraft Maintenance Technician (AMT) reports about the reluctance of their Maintenance Management to address the numerous incidents of electrical shocks mechanics were experiencing after connecting a portable ground power cart to their ERJ-170 aircraft; including aircraft with open fuel tanks.