A question about lightning protection for a sensor mounted outdoors
Products exposed to high E and H field noise may cause errors or damage the interface such as lightning.  The level of immunity depends on the amount of Common Mode (CM) rejection mainly and Differential Mode(DM)  rejection .

Power supplies or Ethernet may be exposed to conducted line transients, from indirect coupled strikes. Power lines  use arc gap quenching contacts at some voltage to protect the Basic Insulation Level rating (BIL) of the equipment attached.  Yet even in homes the protection in power meters is only BIL6 (kV) with arc gaps to earth gnd.

These SMPS and Ethernet interfaces  will always use CM choke on these lines. They may use 2 for improved performance.

The function of the CM choke is by inductance to raise the CM impedance while not raising the DM impedance for power or data transfer.   Then attenuation is greatly improved with HV caps and clamps. 


It is not just a rotated 1:1 transformer , but one designed for a range of frequencies and as perfect a balance as quality tolerances permit.


It also by raising both Lines if CM impedance more effectively balances the impedance resulting in better rejection ratio or CMRR, thus attenuating both CM impulse and DM pulse levels.  
line filters also include Clamps such as MOV, TVS and Gas Discharge Tubes (GDT)  crowbar devices with series current limiting.
depending on the length of the cable the expected E and H fields induced are measured by V/m and I/m from nearby lighting strikes. No assumptions can be made that the bridge will act as a shield or a conduit to high current strikes to protect the cable.



To design such an interface one can rely on Corporate EMI Immunity standards or IEC stds or IEEE standards for impulse immunity, to validate the design.

But to solve this one must consider the interface device limits, the insulation ratings, yet expected transient levels to be much higher than industrial arc welding noise. 

Solutions include:


CM chokes or BALUNs for this application, plastic X,Y caps., TVS clamps , MOV’s, TVS’s, GDT’s shielded twisted pair (STP) balanced DM signalling such as RS-422 or optical solutions.


For more detailed discussions I found many references such as; https://incompliancemag.com/article/designing-ethernet-cable-ports-to-withstand-lightning-surges/