At my VORTAC navigational station I took care of , we had separate cat paths for comm & power then tied all the systems to gather (including bonding of perimeter fence, antenna tower) at a copper plate to earth.
But, for some equipments a functional earthing may be required. Our standards recommend both options, interlinking or not with MET. But, if you are not interlinking FE with MET, keep FE location beyond the influential area of the General Earthing.
Yes, it is true. But it is very difficult to keep away from influential, which is spread across hundreds of meters. So, generally it is suggested to adopt this approach which is prescribed by iec 61000-5-2, iec 60364-4-44, and many other standards.
It shall be a common grid for all. No spacing required. If spacing is provided it shall be away from zone of influence of the other earth grid (typically 100m away). It can be calculated using IEEE 367. 100m of separation not possible, therefore, it is recommended to have common earth
Hi sir, Thank you for your Knowledge sharing. Please advise me, In metro rail 750VDC System here depot is earthing system hence we have to Earth negative potential in rectifier side it's recommended? Or we need to Earth running rail side.
Hi Gaurav. It is not a correct practice to have separate earth for different rooms (reference IEC 61000-5-2, 60364-4-44) 1. Safety hazard - Room reinforcement is bonded to common building earth and separate earth for equipment will lead to difference in potential of feet and hand of the person if he/she touch it. To avoid this in some cases insulation mat of 2.5 mm thickness it provided, however not a correct practice. 2. Having separate earthing can lead to overvoltage transients from one earthing system to the other due to parasitic capacitance that might lead to equipment failure.
Combining the earthing is only to protect the personnel as per above video. In case there is an Signalling equipments/Communication equipment in a closed room the chance of touching the Lightning arrestor earth and equipment earth is very remote. Whether in this case can we go for isolated earths
Thank u sir. How do we connect the reinforcement in the floor, and how much we repeat this? I read some says each floor and some says 30 or 60 meters, I don't remember.
Technical rooms must have a dedicated mesh size of min 5m x 5m (as per IEC 62305-3/4) which must be wire lashed with the structure reinforcement at every 40-50 cm (typical value adopted with no standard reference). For non-technical rooms the mesh size can vary from 10m x 10m to 20m x 20m.
Hi, in UAE when dealing with authorities we need to follow local standards set be them, which are based on old versions of iec, ieee, bs etc. However, within system of metro or mainline we follow IECs
Is neutral earth need to be bonded why in India after transformer we only get 4 wires & there's no earth wire. Earth wire comes seperately from the earth pit.
The neutral must be bonded to ground/earth. In case of house/commercial complex we follow TT or TN system. So in case TT you will find separate earth pit for neutral and separate earth coming to home with RCD at incomer of homes. To reduce EMI this type of system is not found to be effective and thus latest commercial building where we have many sensitive devices we use TN type of earthing. But you are right still in many parts or metros or commercial complex we still follow outdated standards of providing separate earthing for power, sensitive equipment and lightning.
Hi Sahil, I would like to draw attention that in metro practice why clean and power earth may not interlinked with each other? I have seen these in many projects. As they are referring NFPA norms.
Also many designers mentioned IEC 6100-5-2 do not seek to preclude existing installation practice, when they have been shown to perform satisfactory. Special mitigation method might not be necessary when the equipment satisfy applicable emissions and immunity standardards. In perticular , metro installations practices are based on different approaches to EMC that have been found ok for specific installations.
Hi, As per the latest guidelines and metro tenders, earthing & lightning protection system shall be designed according to IEEE 80, EN 50522, IEC 62305 and installation practices shall follow IEC 61000-5-2, IEC 60364-4-44, EN 50174-2 and other standards. Moreover, chapter 7 of CBIP 311 also indicates to adopt common earthing for all which is practiced for mainline AC traction substations. Furthermore, NFPA (NEC 70) article 250.58 suggested to practice common earthing for building and its equipment. Regarding existing metros many failures have been observed, even tough all EMC standards emissions & immunity levels are complied. It is because by providing compliance to relevant EMC standards is not the sufficient that ensure EM compatibility. Installation such as earthing, cables, cable ways, etc. are a major source of EMI and have to be dealt carefully. By providing cross-reference for past experience shall not be encouraged as frequency levels used for operating equipment have drastically changed over the past few years.
At 4:30 you talk about soil capacitance which will provide short circuit to lightning strike to reach clean earth and then the solution to it as per IEC is bonding which is essentially providing it a dedicated short circuit… how does that make sense??? Please make me understand. Wouldn’t this bonding cause lightning strike voltage to damage the equipment???
Initially, before the dielectric breakdown of capacitance, there is a certain high voltage developed across the two separate earth rods (e.g. R1 and R2). Therefore, this voltage acts on the circuits to which R1 or R2 are connected. This situation normalises when breakdown happens and leads to short circuit of capacitance formed. Thus, it is recommended to beforehand itself short by connected R1 and R2. As the bonding connection is very small length, its impedance is very low. Thus, voltage at R1 and R2 are nearly same and no potential difference is created
@@railwayengineeringinsights6463 I get that voltage will be created between R1 & R2, but by comparison this voltage will be much lower than the voltage that will be created between when lightening strike reaches directly at R1 and R2 in bonded state with comparison to earth voltage (i.e 0 volts). In other words, potential difference applied on R2 with circuit of that respective R2 coming in between R2 and surroundings. Wouldn’t it be better than lightening dissipates or gets absorbed in earth at a distance from clean earth rod
When you connect R1 and R2, which is only a very simple case. Typically, by this we means we connect many such paths, there by reducing the impedance and this the potential developed would by I*Znet which is much less that when developed across individual separate earth (I*Z1 and I*Z2). I mentioned impedance as it is a high-frequency phenomenon. If you observe the case of two rods , you can also get a feel that current is shared in a parallel circuit, thereby reducing the potential. Regarding the potential difference for safety, it will be negligible as all points will become equipotential.
Good engineer and teacher. Bravo
Many thanks
At my VORTAC navigational station I took care of , we had separate cat paths for comm & power then tied all the systems to gather (including bonding of perimeter fence, antenna tower) at a copper plate to earth.
Thanks for sharing your knowledge...
But, for some equipments a functional earthing may be required. Our standards recommend both options, interlinking or not with MET. But, if you are not interlinking FE with MET, keep FE location beyond the influential area of the General Earthing.
Yes, it is true. But it is very difficult to keep away from influential, which is spread across hundreds of meters. So, generally it is suggested to adopt this approach which is prescribed by iec 61000-5-2, iec 60364-4-44, and many other standards.
Thank you sir for sharing your knowledge.
👍👍
Can you please tell the spacing between two earthings in earth grid.
It shall be a common grid for all. No spacing required. If spacing is provided it shall be away from zone of influence of the other earth grid (typically 100m away). It can be calculated using IEEE 367. 100m of separation not possible, therefore, it is recommended to have common earth
thank you very much for such an informative video
🙏
Hi sir,
Thank you for your Knowledge sharing. Please advise me, In metro rail 750VDC System here depot is earthing system hence we have to Earth negative potential in rectifier side it's recommended? Or we need to Earth running rail side.
Hi Sahil, Is it okay to have separate earths if both racks are in different rooms? or in same room but far enough from each other?
Hi Gaurav. It is not a correct practice to have separate earth for different rooms (reference IEC 61000-5-2, 60364-4-44)
1. Safety hazard - Room reinforcement is bonded to common building earth and separate earth for equipment will lead to difference in potential of feet and hand of the person if he/she touch it. To avoid this in some cases insulation mat of 2.5 mm thickness it provided, however not a correct practice.
2. Having separate earthing can lead to overvoltage transients from one earthing system to the other due to parasitic capacitance that might lead to equipment failure.
Combining the earthing is only to protect the personnel as per above video. In case there is an Signalling equipments/Communication equipment in a closed room the chance of touching the Lightning arrestor earth and equipment earth is very remote. Whether in this case can we go for isolated earths
Thank u sir. How do we connect the reinforcement in the floor, and how much we repeat this? I read some says each floor and some says 30 or 60 meters, I don't remember.
Technical rooms must have a dedicated mesh size of min 5m x 5m (as per IEC 62305-3/4) which must be wire lashed with the structure reinforcement at every 40-50 cm (typical value adopted with no standard reference). For non-technical rooms the mesh size can vary from 10m x 10m to 20m x 20m.
Hi Sahil, Which standards are followed in UAE & Dubai??
Hi, in UAE when dealing with authorities we need to follow local standards set be them, which are based on old versions of iec, ieee, bs etc. However, within system of metro or mainline we follow IECs
Pls make video on SPDs
Sure soon video on SPD will be uploaded
What is SPD that is mentioned in the video? Can you please elaborate.
SPD is surge protection device that is used to limit overvoltages caused due to lightning, switching, etc.
Is neutral earth need to be bonded why in India after transformer we only get 4 wires & there's no earth wire.
Earth wire comes seperately from the earth pit.
The neutral must be bonded to ground/earth. In case of house/commercial complex we follow TT or TN system. So in case TT you will find separate earth pit for neutral and separate earth coming to home with RCD at incomer of homes. To reduce EMI this type of system is not found to be effective and thus latest commercial building where we have many sensitive devices we use TN type of earthing. But you are right still in many parts or metros or commercial complex we still follow outdated standards of providing separate earthing for power, sensitive equipment and lightning.
Hi Sahil, I would like to draw
attention that in metro practice why clean and power earth may not interlinked with each other? I have seen these in many projects. As they are referring NFPA norms.
Also many designers mentioned IEC 6100-5-2 do not seek to preclude existing installation practice, when they have been shown to perform satisfactory. Special mitigation method might not be necessary when the equipment satisfy applicable emissions and immunity standardards. In perticular , metro installations practices are based on different approaches to EMC that have been found ok for specific installations.
Hi,
As per the latest guidelines and metro tenders, earthing & lightning protection system shall be designed according to IEEE 80, EN 50522, IEC 62305 and installation practices shall follow IEC 61000-5-2, IEC 60364-4-44, EN 50174-2 and other standards.
Moreover, chapter 7 of CBIP 311 also indicates to adopt common earthing for all which is practiced for mainline AC traction substations.
Furthermore, NFPA (NEC 70) article 250.58 suggested to practice common earthing for building and its equipment.
Regarding existing metros many failures have been observed, even tough all EMC standards emissions & immunity levels are complied. It is because by providing compliance to relevant EMC standards is not the sufficient that ensure EM compatibility. Installation such as earthing, cables, cable ways, etc. are a major source of EMI and have to be dealt carefully.
By providing cross-reference for past experience shall not be encouraged as frequency levels used for operating equipment have drastically changed over the past few years.
Gold!
Many thanks
At 4:30 you talk about soil capacitance which will provide short circuit to lightning strike to reach clean earth and then the solution to it as per IEC is bonding which is essentially providing it a dedicated short circuit… how does that make sense??? Please make me understand.
Wouldn’t this bonding cause lightning strike voltage to damage the equipment???
Initially, before the dielectric breakdown of capacitance, there is a certain high voltage developed across the two separate earth rods (e.g. R1 and R2). Therefore, this voltage acts on the circuits to which R1 or R2 are connected. This situation normalises when breakdown happens and leads to short circuit of capacitance formed. Thus, it is recommended to beforehand itself short by connected R1 and R2. As the bonding connection is very small length, its impedance is very low. Thus, voltage at R1 and R2 are nearly same and no potential difference is created
@@railwayengineeringinsights6463 I get that voltage will be created between R1 & R2, but by comparison this voltage will be much lower than the voltage that will be created between when lightening strike reaches directly at R1 and R2 in bonded state with comparison to earth voltage (i.e 0 volts).
In other words, potential difference applied on R2 with circuit of that respective R2 coming in between R2 and surroundings.
Wouldn’t it be better than lightening dissipates or gets absorbed in earth at a distance from clean earth rod
When you connect R1 and R2, which is only a very simple case. Typically, by this we means we connect many such paths, there by reducing the impedance and this the potential developed would by I*Znet which is much less that when developed across individual separate earth (I*Z1 and I*Z2). I mentioned impedance as it is a high-frequency phenomenon. If you observe the case of two rods , you can also get a feel that current is shared in a parallel circuit, thereby reducing the potential. Regarding the potential difference for safety, it will be negligible as all points will become equipotential.
Thank u very much