Final answer:
Technicians need to know how to safely turn on and off water and gas lines, and they must be familiar with the three-wire system and the use of a GFCI to prevent shocks.
Step-by-step explanation:
Installation technicians need to understand how to properly turn on and off water and gas lines to ensure the safety and proper operation of appliances. This knowledge is crucial as a technician must be aware of the correct procedure to prevent any potential hazards, like electric shocks or gas leaks. Technicians must be familiar with the three-wire system, which involves live/hot, neutral, and ground wires. Additionally, they should know the importance of a ground fault circuit interrupter (GFCI) which prevents electric shocks by detecting and responding to loss of current.