I have a PCB in the field that is put in an enclosure box and is placed on a pole in an open environment.
My question is, if the PCB does not have the power supply connected, can ESD still damage the PCB or any of the sensitive components?
Please correct me if I'm wrong, but just like normal voltage signals that go from higher potential to lower potential, ESD would try to find the smallest path to ground.
So, even in the worst case if a lightning bolt does hit the pole, the charge would rather travel straight towards the ground than touching the PCB board (not powered up).
Best Answer
ESD doesn't need a pathway back to ground to be destructive, almost everything looks like a conductor when voltages are in the thousands of volts. Once an ESD event gets started it causes a current avalanche and materials (even air and insulative materials) start to break down and become conductive and destroys anything in its current pathway.
Source: https://nepp.nasa.gov/index.cfm/6095
The picture above shows a capacitor on an IC, which has a layer of insulation between it and the other side of the capacitor. The ESD event blew right through the insulator.