DGMS on Flexible Trailing Cables

No. DGMS(Tech.)Circular DGMS(Tech.)Circul ar No.2

rd

Dhanbad, dated the 3  May, 2002.

To The Owner, Agent and Manager of all the Coal Mines. Subject: Recommended Code of Practice for Operation and Maintenance of Flexible Trailing Cables Associated with Mobile Machines.

The present practice of manual handling of flexible trailing cables is fraught with danger. In view of this it is suggested that where the machines are required to move, manual handling of cables should be avoided/minimized as far as practicable where circumstances permit by the use of properly designed, installed and maintained cable reeling or handling devices. As the above procedure calls for modification in the design of the machine and will take some time to materialize, the following measures should be adopted to ensure safety in use of flexible trailing cables with electrically operated loading machines. (i) Where flexible cables are not required to move, they should be effectively supported and protected against physical damage. (ii) Where they are required to move, concerted and focused effort should be made to train machine operators and cable men in safe operation of electrically operated loading machines and handling of the associated flexible trailing cables. (iii) Cablemen/cable handlers/SDL operators are required to handle electrically live flexible cables. Handling such live cables should be considered a specialized job and as such they should be considered under the category of “competent person” and hence should be properly trained and authorized in conf9ormity with the provisions of the Rule 3 & 36(2) of the Indian Electricity Rules, 1956. (iv) Such cable handlers should be provided with suitable personal protective equipment such as hand gloves and other suitable appliances as deemed fit and their use should be ensured to ensure safety of such workmen. As regards repair of the trailing cables the following measures are considered to be in order. (i) Provision should be made in the colliery workshop with requisite equipment/appliances for the efficient maintenance and repair of the trailing cables The floor space should be sufficient to permit the cable to be laid out for detailed examination, test and repair and to accommodate the necessary benches and appliances.

 (ii) Puncture in the outer sheath may be located readily by means of ordinary spark testing appliances or other instruments. Special spark testing appliances/Instruments/Meggar Insulation Tester that are available should be used for detecting and locating fault between conductors. If the bulk of the cable is waterlogged it should be dried out, say by means of a vacuum impregnator such as is used for drying armature or by other means before any repairs are attempted. One method of drying out local moisture is by gently warming the cable on each side of the damage. High temperature must be avoided. Another method which is claimed to be very effective is to direct a strong stream of hot air from all electric hair dryer or any other similar apparatus on to the joint and cable near it for about 20 minutes. While carrying out vulcanization, due importance is to be given to the insulation resistance value of the cable at every step/stage of vulcanization process. (iii) Where two or more of the core conductors in a cable are joined, it is essential, in order to preserve flexibility that the joints shall be widely spaced. (iv) It must be recognized that there is a limit to the extent to which a particular length of a cable may be repaired and that a stage is reached at which the cable should be scraped and a new one put in service. The above notes are guidelines for repair and maintenance of flexible cables and is not exhaustive. Relevant Indian standard, manufacturer’s instruction and guidelines and the expertise of the skilled workmen should also be taken into consideration for maintenance and repair of flexible cables for mobile machines in mines.

( A. K. Rudra ) Director-General of Mines Safety.