For variuous reasons I need to add an extra transformer between external ethernet connection and an ethernet device that has magnetics built in.
The reason being, among others, to elimnate possible high (up to 1500 V) common mode voltages and provide ESD protection. Such high voltages are unacceptable for my application.

The question here is what would be the downsides of this solution?

* EMC/EMI problems
* Termination problems
* IEEE 802.3 standard violations?

I did try to find some answers for the question in the standard. My conclusion is that as long as the attenuation of additional transformer is small enough, and 2 V differential voltage is quaranteed it should not be a problem?

The other aspect is that common layout reccommendation is that distance between PHY and magnetics should be kept around 5 cm (2 in). I will noe have 0.5 m, is it because of Bob smith termination?

Would it make sense to omit the Bob Smith termination of my transformer (on the right), because the device already has one?

[![enter image description here](https://i.stack.imgur.com/Y1ahU.png)](https://i.stack.imgur.com/Y1ahU.png)