You have discovered a common mode current on the metallic cable sheaths of your building riser cables. What is the MOST likely cause for you to investigate?

Lack of cable protection addresses physical damage such as crushing or abrasion and has no relationship to the generation of common mode currents on metallic sheaths.

When two physically separate ground references exist in a building, a difference in electrical potential almost always exists between them. That potential difference drives current through the metallic cable sheath, which becomes an unintended return conductor between the two grounds, producing the observed common mode current. Resolving this requires establishing a single-point or equipotential bonding ground system to eliminate the voltage difference.

Improper secondary protection refers to inadequate surge or lightning protection devices and does not explain steady-state common mode current on riser cable sheaths.

Improper physical protection concerns mechanical damage prevention and does not produce the electromagnetic condition of common mode sheath current.

Improper placement or termination may cause crosstalk or signal integrity problems but is not the root cause of common mode current flowing on cable sheaths.