Steve wrote:

What it doesn't explain of course is how these discharges get into your system, if it is as well isolated as you say.

Exact! Proper grounded and shielded electronics will hardly fail only because of ESD events! There MUST be a mistake somewhere, which results in an entering of ESD events into system. Symmetrical signal routing in combination with concept of grounded Faraday cage, means use of shielded cables everywhere with shields grounded at both ends, is a good remedy against ESD events!

I assume that spiky discharge current of ESD event takes the wrong path to ground, not via protection earth or shield but via some signal line. But if grounding scheme is routed properly, ESD current (or main ESD current) even need not to flow across cable shields!! I stay with my opinion: There's something wrong with the ground routing and shielding.

If I could have a look at the wiring scheme I would probably fimd the mistake within short time...

Kai