Network Cabling Minimum Bend Radius

I know certain types of cabling have a spec for min. bend radius. I guess the detrimental affect of violating this would be slower or lost communications. But why would a smaller bend radius do this? What is the physics behind it?
I'm asking in particular about Modbus plus cabling. I have a site with multple drops connected with Modbus plus cabling and taps. The extra length of cabling in one of the cables is folded in the Panduit. Is there a spec as mentioned above for it?
I'm also generally concerned with Profibus and Ethernet cabling. Our panel shop coils then folds the extra ethernet cabling in the Panduit and ties it together with wire ties.

I mainly use bend radius specs for things that flex and move. If it is to remain static in panduit, I think you have more, uhm, flexibilty.

godfrey said:

I guess the detrimental affect of violating this would be slower or lost communications. But why would a smaller bend radius do this? What is the physics behind it?

Click to expand...

Hogwash! It is not "physics" as far as electron movement. It is losing the physical integrity of the cable!

Bending the cable with too small of a radius will damage the sidewall of the outside jacket of the cable.

Also check out:
http://en.wikipedia.org/wiki/Minimum_bend_radius

If you coil high speed network cables in too many loops, the centrifugal force of the electrons will force them to the outside of the conductor and they can get stuck in the jacket of the cable. With profibus cabling in particular I have seen the electrons actually get dizzy and fall right through the jacket.

Seriously though the minimum bend radius is a measurement to prevent mechanical damage to the conductors as well as the insulation.

As far as the implications of a bunch of coiled cable picking up noise, that's a whole other issue.

Unless the cable manufacturer says otherwise, my rule of thumb is that the radius be no less than five times the diameter of the cable. For certain RF cables, the limit is ten times the radius (meaning for coax type cable, it is more important not to alter the the physical relationship between the center and outer conductors).

Well actually the cat 5 and above cables for ethernet rely on a very strict twist arrangement. Bendind these cable too tight alters this arrangement giving a degrdation in the cables performance.
Regards Alan Case