Why is there a connection to ground in this RJ45 jack schematic ?

[tigrou]

Why is the center tap of the transformer "connected" to ground with a capacitor in between ?
Would the transmition of data still works without that connection (with some drawbacks) ?
The capacitor is rated 2KV which is far more than voltage that what goes in a RJ45 cable.

AFAIK the transformer is to provide some galvanic isolation between the two devices (eg: the RJ45 cable could connect two buildings with that have potential difference)

[AndyC_772]

You're quite right that the transformer is there to provide isolation, which is a required part of the Ethernet spec.

The capacitor to GND is there for EMC. Connecting it to a locally quiet ground means there is zero common mode component on each of the differential pairs, and if the differential components cancel (as they should, in theory), that results in minimal emissions from an unshielded cable.

It's rated 2kV in order to match the dielectric strength of the transformer; this rating is chosen so as not to expose the user to a shock hazard if the cable is shorted to the mains supply.