Do you currently have a field that tracks availability (available and unavailable)? One idea is to add a third value called "Broken."
1. In your database properties, find the domain that has the available and unavailable coded values. Add a third value called Broken. In my case, the domain is called Fiber Availability Indicator.
2. In order to see the Available field in Connection Manager, it needs the Field Model Name FIBERCONNECTIONDISPLAYFIELD. Find your F_Fiber table in ArcCatalog, and using the ArcFM Properties assign that Field Model Name to the Available field.
3. In the map, start editing. Select the cable that contains the broken fiber. Then, in the ArcFM Attribute Editor, find the specific fiber and change its field value to Broken. In my case, the Blue-Orange fiber is broken. Make sure you press the Update button in the Attribute Editor to lock in your edits.
4. Because you made the Available field visible (step #2 above), you will see this value in Connection Manager.
Does that help?
Another option, if you've implemented the default data model many of our clients do you may already have a "status" field for each fiber object. Typical options assigned to the field's domain are "lit", "dark", and "defective". I think this field is meant to be used in conjunction with the "Availability" field that Andrew mentioned, so you'd set the strand's availability to "Unavailable" (this action will update the availability count for the parent cable feature) and then specify the strand's status as "defective".