Final answer:
Experts check power transmission lines with the back of their hand to ensure they are de-energized because it reduces the risk of involuntary gripping onto the conductor in case of an electric shock.
Step-by-step explanation:
The question pertains to the safe practices employed by professionals before working on overhead power transmission lines. These experts are responsible for ensuring that the lines are de-energized, and they often perform a final check by touching the line with the back of the hand to confirm that the voltage is indeed zero. This specific method is used because if there were to be an electric shock, the muscle contractions caused by the shock would likely force the person's hand to close, which could cause them to grip the conductor if using the palm. However, using the back of the hand reduces the risk of involuntary gripping and getting stuck to the conductor. This safety procedure is critical for electrical engineers and maintenance workers who are often called out to repair high-voltage equipment after incidents like storms, in addition to other challenges such as removing animal carcasses from transformers.