SB16 and SB17 solder bridge on a nucleo-f207zg within ethernet circuit stage

[genisuvi]

When you look at your Nucleo-f207zg board, ethernet stage, you can see: 

1. (CN14) RJ45 connector.

2. (U11) magnetic-transformer.

3. (U10) TVS diodes for diff pair signals.

4. (U9) LAN-PHY device.

First appreciation:

Then you can see that not connected RJ connector pins, RJ shield and magnetic CT pins are connected to some kind of ground I guess it is not connected to any board ground, despite the own shield connector. So this shield will get a ground contact from a cable ground if cable is shielded.  

Second appreciation:

There are SB17 and SB16 solder bridges on the board, open state by default, between power stage ground and shield ground node. There is no information about these two bridges on Nucleo's datasheet. 

My questions:

- I'm wondering if the bridge is offered in order to join these two grounds directly or using ferrite, capacitors, etc..?

- When should I connect these two grounds and when I shouldn't? what is better? to be connected or not?

[InsignificantBit · Accepted solution]

The topic of connecting ethernet shielding to the ground of the board is complicated one.

In this case, the reason for omission of the connection is largely because it is not needed for a development board, or the connector was possibly supposed to be used as a non-shielded variant.