Yes, lightning can still damage an electrical appliance even if it's turned off. When lightning strikes a power line or a nearby object, it can induce a powerful electrical surge into the electrical system. This surge can travel through the power lines and enter a home or building through various paths, including electrical outlets and telephone lines.
When an appliance is turned off, it is not actively drawing power from the electrical outlet, but it is still connected to the electrical system. The electrical surge from a lightning strike can find its way into the appliance through its power cord, phone line, or other connected cables. The surge can cause damage to sensitive electronic components, even if the appliance is not powered on at that moment.
To protect appliances and electronic devices from lightning-induced surges, it is recommended to use surge protectors or Uninterruptible Power Supply (UPS) systems. Surge protectors are designed to divert excess voltage from a lightning strike away from connected devices, reducing the risk of damage. UPS systems, in addition to surge protection, provide battery backup power to allow safe shutdowns during power outages, further safeguarding appliances and electronics.