When is it allowed to use non-isolated PoE?
When is it allowed to use non-isolated PoE?


Never.

IEEE 802.3at specifies that isolated power supplies be used. If it doesn't use isolation then it's not called PoE.


  We are debating whether to use an isolated or a non-isolated supply.


It's not PoE unless you use an isolated supply. It becomes something else.

Think about what ethernet does - it provides massive insulation against indirect lightning surges by using magnetically coupled data interfaces. This isolation would be ruined by a non-isolated DC power supply. Not only would it become much more susceptible to surges but the impedance balance of signals would be significantly compromised and speed performance would be very poor.