Does the Jack-PC have power switch? How can I power it down?
No. The device is always powered on. If not actively used - power is reduced automatically to standby power. You can turn-off the monitor if you want or you can set the device to shut-down the monitor after pre-defined inactivity time. This will not only conserve energy but also will not require any user action to turn on or off the workstation.
What happens if a lightning strikes the building and getting into the LAN cabling?
Jack-PC has multiple high-voltage protection circuits. These circuits were designed to sustain and isolate very high electrical pulses. As with any other NIC - if energy exceeds certain value - permanent damage will occur. This type of thin-client is not different than any other thin-client or computer in terms of lighting vulnerability.