Erik said:
With the enclosure connected to 'protection ground' the only RF you get in is the noise on the protection ground plus a wee bit from the enclosure to protection ground wire impedance.

Kai replied:
Remember, this thread is about ESD! What, if the enclosure 2 is hit by an ESD event?? Then, the enclosure will be thousands volts higher than the internal electronics!! Only the cap between signal ground and enclosure, or the direct connection of course, can then force the enclosure on the same potential as the internal electronics. Only then the enclosure can act as a shield.

With the enclusore grounded ("protection ground") you will, in the case of an ESD event get a short spike on the enclosure due to the inductance in the wire to protection ground. If you have a cap between the enclosure and signal ground, that will be a less resistant path then the inductance of the wire.

I have, In one instance, seen the cap you promote exploded from an ESD event, that hardly indicate that such a cap is beneficial to limit the effect of ESD penetration.

Now, let us agree that the 'science' of noise and ESD protection is quite fuzzy and many opinions exist.

I have seen the cap you promote suggested as a means of "providing some shielding when the enclosure (mistakenly) is not grounded".

Erik