A normal static snap from the tip of your finger might reach voltages of 10kV, while the highest recorded ESD voltages are around 30kV (30,000 volts). That’s more than enough to fry sensitive components, even if they are protected by a carefully designed board.
What does the damage with ESD is the fast high current waveforms and fast magnetic (H-field) or electrostatic (E-field) disturbances. These can induce voltages or currents in nearby sensitive circuitry, and corrupt data or cause spurious failures.
What you should get into the habit of doing whenever you are around controllers is wearing a grounded anti-static wrist strap connected to the panel housing. Any static electrical charge that builds up on your body is then immediately transferred to ground through the case of the controller.
Depending on how you are working, experienced technicians can also use a few tricks for controlling static electricity around controllers and control modules. One trick is to leave the circuit board laying on top of an antistatic bag or antistatic foam whenever possible.
Another is to leave an ungrounded device plugged into an AC outlet with the power switch turned off. This places ground on the metal case. The technician then works with one hand always touching a metal part of the case. Any electrical charge that builds up on your body is then immediately transferred to ground the same as with an anti-static wrist strap.
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