I have two buildings separated by about 250m and plan to run fiber between them. Mikrotik routers will be in each building and was planning on using gigabit S-85DLC05D modules.
What fiber should I use? My reading says that 50/125micron OM3 category fiber but the contractor says 62.5/125 would be OK.
My advise is don’t install any multi-mode fiber between buildings. Only go with single-mode for anything between a building that may have distance. If you ever plan on going over 1GigE on that fiber you will need something other than 62.5 micron. 10GigE only goes 33 meters on 62.5 for example. It can go further on OM3 and OM4 cable but my advise is just avoid it and go with single mode.
As someone who is in the process of replacing 20+ year old FDDI grade 62.5 MM fiber on a campus don’t do it. The single-mode fiber will last at least through 100GigE. Multi-mode even 50 micron OM4 will only last through 10Gig.
My advise is between buildings install single mode. In building between closets install a combo cable with both single-mode and multi-mode.
These days with 1Gig optics there isn’t really a price difference. With 10GigE there still is to a degree but that gap will change.
I should note you will need to change from the optics you mention to S-31DLC20D.