EV-ADES1830 S8~S16 TVS

These are surge voltage clamps;
The diodes are attached to higher channels only since they are the ones with highest potential (and hence highest current flow) and if we can clamp those voltages down to a safe level below abs max the part will be able to survive. Normally when there is a surge, they get divided among all channels but since higher channels are already at a higher potential, the voltage (and current flowing) there gets comparably bigger than the lower channel. This is the reason why we add them to the higher channels.D23 is added so that there won't always be leakage through the diodes attached to the S-Channels (since they are forward biased) which will cause the measurement errors, and this diode will only get activated when there is a surge transient. Ideally if they can add TVS to all channels that would be most ideal (but it is expensive to do that).

Thanks for your reply. TVS can be used as a reserved option in the circuit diagram.

Yes true, but since we have a working cheap solution there was no need to add all the possible options.