my understanding is that the Esri Geometric Network has issues with features being traced over/stacked on top of one another.
When I first asked Esri Support this question, I was advised that this cannot be done as it would cause issues within the Geometric network.
Another issue you may encounter would be placing coils / slack loops. If you try to place it on one cable, you'll find that it places on top of the top cable, which may not be correct?
I've used the Trace tool with Ctrl+O for Offset. I've specified an offset of 0.02m which is sufficient to resolve this issue (in my experience) but and when zoomed out, displays fairly well.
We are using Fiber Manager,
We (planed and documented) blown 2 cables with 192 fibers in each in a different microduct., part of 7microdusts bundle. On a map we placed one "7 microducts" and two blown cables with 0.1m offset. After connecting the fibers in both sides (source and target) we associated 1 cable to the ""Blue" microduct and second cable to the "Green" micro duct.
You can use "Fiber Trace" button in Fiber Manager tool barfor tracing the ducts bundle and every single (or more) fibers in each cable.
In total there are only three items on the map.