ITU-T K.29 PDF

Introduction

When telecommunication cables need protection against danger and interference from a.c. power and traction lines, lightning and corrosion, it is convenient to provide coordinated measures to assure protection against all these sources.

Since corrosion problems appear mainly on cables below ground, this Recommendation suggests coordinated protection schemes for such cables.

The environment is the main factor to be considered in deciding whether or not protection is necessary, in particular the following factors should be taken into consideration:

a) protection against lightning:

– keraunic level,

– orographic conditions,

– altitude,

– soil resistivity (in the top layer);

b) protection against effects of electric power and traction lines:

– soil resistivity (in deep layers),

– inducing current,

– distance between the telecommunication cable and the electric power and traction line;

c) protection against corrosion:

– soil resistivity (in the top layer),

– corrosive components (ions) in the soil,

– stray currents in the soil (sources of d.c. stray currents are d.c. traction rails, earthing electrodes associated with d.c. sources, metallic structures with cathodic protection and the like).

Protection of underground communication cables against corrosion is achieved mainly with protective plastic coverings on the metal cable sheath.

Regarding the environment, the installed cable behaviour is different if an insulating or conductive plastic material is used as protective covering. Therefore, coordinated protection schemes are also different and the two cases should be considered separately.