Guarding, Service lines from overhead lines, Earthing & Safety Regulations 70 to 73.

Panel Discussion on Electrical Safety Regulations - Question 9

Regulation 70, 71, 72 and 73 – Are they really implemented by the supply companies across India.

The regulations are

70 - Guarding

71 - Service lines from overhead lines

72 - Earthing of poles at distribution

73 - Safety and protective devices

Answered by Shri C. P. George, Deputy Chief Engineer (Rtd.) Kerala State Electricity Board Limited Kerala State Electricity Board Limited

Regulation 70 to 73 of CEA regulations are concerns with public safety from supplier licensee's network. To be more specific, they are meant to protect the public from electricity hazard due to conductor snapping or lack of statutory clearance specified.

Regulation 70 specify proper earthing of the guarding to ensure enough fault current to enable automatic tripping of the source in the event of snapping of a live conductor, which touches the guard wire.

Regulation 72 specify the bonding of every metal parts in every support pole which is to be earthed appropriately by a continuous earth wire which is fastened to every pole support where all metal parts are bonded together. Again it is stated that the continuous earth wire is to be connected to earth at three points at every kilometer. Thus it is obvious that the regulation is specifying a safety earthing system with an earth conductor throughout the network which is linked with the bonded metal parts in each pole support. More over the GI support of the service wire specified in regulation 71 is also supposed to be linked with the earthing system made with the earthed conductor and the bonded metal parts in each pole.

As such, we have a TN-S system (if complied appropriately) and a safety earth terminal at consumer premise shall be available if we link the GI wire used for the whether proof support to the earthed terminal of the consumer.

As per regulation 73, every OH line by the supplier shall be protected with earth guarding for rendering the line electrically harmless in case it breaks .

We are aware of the fact that to render a snapped conductor of electricity harmless, we need to have a protection system which shall isolate the supply from the source. This protection system includes a simple kit-kat fuse to the most modern circuit breaker in the system.

All these equipment ensures the isolation of the downstream supply, in case it senses a fault according to the pre-set value and design.

Generally these protection system acts based on the technology and principle of

  1. over current

  2. earth leakage current &

  3. the variation of the impedance/ electrical property of the of the OH line conductor

We need to know that for LT & HT, the proven technology for protection is “over current” and “earth leakage”. Thus regulation 73 of CEA safety regulation 2010 is of greater importance in ensuring public safety in our electricity distribution system. The compliance of regulation 73 shall ensure better clarity in tripping signals and ensures the isolation of the downstream supply with far better reliability.

But is observed that we have not even considered the strict enforcement of the relevant provisions in our distribution network to ensure a better safety environment for public from our distribution system.

For strict enforcement, we need a reliable protection system that SWTICHOFF the source automatically. For that we need enough fault current to trigger the tripping mechanism on snapping of the conductor and same shall be achieved by an earthed system of appropriate design where the live conductor, (in the event of snapping), shall come in contact with it. And this requirement again recommends a TN-S system of distribution unless we opt for a TT system with RCCB protection for LT distribution system.

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