1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 , TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITUCONSTRUCTION, INSTALLATIONAND PROTECTION OF CABLE AND OTHERELEMENTS OF OUTSIDE PLANT!00,)#!4)/.G0G0/b) the danger of corrosion on neighbouring underground metallic structures is increased.Joint protection of
2、telecommunication cables with other structures can be reasonably applied in the cases when:a) nearby underground structures are at a distance generally not exceeding 50 metres;b) the buried plants cross each other;c) the ground beds or reactive anodes of a cathodic protection system have a harmful i
3、nfluence on nearbyunprotected plants.Joint protection of telecommunications and power cables in accordance with reference 1 may be consideredwhen the potential to earth of the telecommunications cable does not exceed the safe voltage required by local ornational safety rules in the event of an earth
4、 fault or short circuit on the power supply system.Joint cathodic protection should provide on the protected plants potentials which are within the values indicatedin reference 1.In the case of joint protection it may be possible to use devices which automatically control the current outputof the ca
5、thodic protection equipment.3 Conditions for electrical bondsSpecial bonds are used to provide electric contact between jointly protected plants. Bonds may be direct, orprovided with a resistor (to limit the current) or polarized.Direct bonds may be used in the following cases:a) when underground me
6、tallic structures of the same type are crossing or approaching each other;b) when the provision of bonds between structures of different types does not reduce the efficiency of theprimary cathodic protection system.Resistor bonds which control the current applied to different types of plant should b
7、e used when potentials onthese structures should be controlled.2 Volume IX - Rec. L.7Polarized bonds should be used:a) for joint drainage and cathodic protection systems;b) to prevent current flowing from a pipeline to telecommunication plant;c) to protect against failure of the cathodic protection
8、equipment.Bonds should not be installed between buried structures and power supply cables and equipment unless it issafe to do so in the event of a fault on the power supply system and it is in accordance with local and national safetyrules.4 Monitoring the performance of joint cathodic protection d
9、evicesThe performance of joint cathodic protection devices should be monitored by means of:a) routine examination of protective devices and equipment;b) routine measurements of interaction potential differences with the protection equipment switched on andswitched off at all the plants incorporated
10、in the joint protection system, in compliance with local acceptedprocedures.When tests or changes are made on the joint cathodic protection system, the presence or agreement of therepresentatives of operating agencies whose underground structures are incorporated in the joint protection system isrecommended.Reference1 CCITT manual Outside plant technologies for public networks, ITU, Geneva, 1988.
