Consider a circuit like this... 

![schematic](https://i.stack.imgur.com/CKal2.png)

[simulate this circuit](/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fCKal2.png) – Schematic created using [CircuitLab](https://www.circuitlab.com/)

What happens to the voltage seen by the MCU between VCC and GND when this circuit takes a positive ESD hit to the bottom terminal of SW1?

The circuit ground is not connected to earth ground. L1 is parasitic inductance at the very high dv/dt that results from the ESD strike.

* Does the MCU blackout?
* What is the best defense for this failure mode?