Q:

best practices in detecting relay contacts status

Currently i'm experimenting with 12VDC energy meters latching relays and at least for me the feature of detecting status of contacts ( required by some clients ) which is built in as in the diagram below is quite interesting. Now i need to interface it to a microcontroller safely. At the top of my head i may think of using an optocoupler but my understanding is i need to isolate the grounds ? thus making the design a bit pain in the kneck, is this the only feasible method or are there other approaches ?. 

TL;DR pins 4 and 5 switch on / off depeding on status of relay, how do i sense/ measure status of the latch with those pins? 

A:

If the Auxiliary contacts are not currently used, you just connect them to a microcontroller digital input as you would any other switch - something like so:

simulate this circuit – Schematic created using CircuitLab
If the auxiliary contact is already used, you may have to use an opto-coupler or perhaps an additional relay, depending on what is connected to the auxiliary contacts of the contactor.

