Earth Resistance Value

IS 3043 says the resistance of the earth pit shall be as low as 0.5 ohm and having maxi cauurent carrying capacity.Also for pipe electrode it should be of 50mm dia and 3 mtrs length also the distance between two distinct EP should be 4-6 mtrs.many more to add on this what u requ?

The reply above is confirmed correct.

Thank you

Just meeting the requirements of a code such a IS 3403 does not assure that thing will work as intended. There are soils the ground rod won't always work as it should in. As a designer or engineer its your job to see thing function as they should not just meet the letter of the law. Sometimes its hard to both.

Getting a low resistance too earth from a ground rod can be problematical in some soils. The ones that are simply high resistance can be overcome by using a 2 inch/200mm OD copper pipe with 1/8-3/16 inch/3-5 mm hole every 4- 6 inches/100-150 mm in a radial pattern around the pipe. Then use a pointed rod the tube fits over to drive the rod down. If the ground is dry and hard and there is a source of water a snug fitting pipe with a fitting for a water hose to use water pressure to jet the rod down.

Once the pipe is in place fill it up with salty water to make a larger low resistance contact to the ground.

In very dry areas with heavy clay soils that are bad about cracking the rod will introduce a anomaly for a crack to form. It place in fill that is not properly compacted it is possible for the ground to crack to the point the rod is loose a crack in the soil. That can be over come with the pipe with drill holes by periodically watering filling the pipe with water. An automatic system could be made to water the rod if the resistance fell below a certain point. It would need warnings to assure the water wasn't ruing in a gopher hole or other feature that can't be filled up. But if the system is automated that is not to big a deal.

In low resistance soils, soils were rock is closer than 8 feet US code or 3 meters IS 3043 to the surface the US code has ways to use more rods. In dry areas with heavy clays that crack away form the rod finding a place to go full depth is more important to get the rod as deep as you can than it is in moist areas with sandy soils.

Also use single point grounding and bring all the wires into a building at one point. Proper grounding to the single point ground should be observed by every contractor to get the best lightning protection. If more than on ground rod is needed the other rods should be tied to the one below the wire entrance point in a star pattern of one cable to each rod. Ideally they should be copper and all joints welded with termite. But most systems I have seen use copper clad steel rods and clamps not welds.

A properly grounded system is pretty well immune to lighting if the lines that come into it are all properly protected out on the pole and on the full run. In the USA the rural telephone lines seem to be the worst offenders on carrying lightening into the house in my part of the world. The boom in internet and the massive build out of telephone lines that started even before that and the incorporation of the telephone cooperatives that literally ran a single wire on the tops of fence posts and use the earth for a return path and had as many people on a party line as they could get to work they knew if the call was for them by the ring pattern [ours was 2 longs and a short ring on line 85 F2] has taken years to get up to code. Many were run by the users and central was in someone's home.

Grounding is an art of its own and ignore any part of the code at your peril. The code is probably not strict enough and should include at least an 8x8 ft/3x3m grounded steel or copper sheet at the point all wring enters the building. The wiring should enter at the center of the sheet and it would be difficult to install. All panels and such should ground to the sheet with very sort ground straps.

One place for lightening to generate a potential difference in the wires that come in the building or in the wires in the building its self are an invitation for problems. I have had problems from something as simple as a network cable that made a single wrap around a 110 AC power cord. That generates almost nothing in terms of voltage. I had CAN Vehicular network running on two legs of 220 volt AC that had 83 volts AC of tramp current on them and they worked just fine. I found it on a hot day when I got bit when I put a sweaty arm across two of the cases. So just because thing work fine doesn't mean they are OK. And when you have problems then can be so small it is almost impossible to find them.

A pair of alligator clips on a wire to clip what appear to be already connected grounded parts together can make you look awful smart. A VOM with a sensitive FET input can do the same. The 83 volts of tramp current would show up on cheap volt ohm meter. But would on a good one or on a scope.

Gordon

Two words:

Ufer Ground

The Purpose of an earthing system is to provide as nearly as possible a surface under and around electrical Installation to be at uniform potential and as nearly zero or absolute earth potential as possible. The purpose is to ensure that generally all parts of the equipment, other than live parts are at earth potential and that attending personnel are at earth potential at all times. By providing such an earth surface of uniform potential under and surrounding the station, there can exist no difference of potential in a short distance big enough to shock or injure an attendant when short circuits or other abnormal occurrences take place.

Before designing earthing system the step and touch voltage should be under stood.

Step Voltage : The potential difference between two points on the earth's surface separated by a distance of one pace, that will be assumed to be one metre in the direction of maximum potential gradient.

Touch Voltage : The potential difference between a grounded metallic structure and a point on the earth's surface separated by a distance equal to the normal maximum horizontal reach of a person, approximately one metre.

So the earthing should me initially made as per specification and should be maintained as per requirement to ensure protection and safety.

For detailed Knowledge of earthing Please refer the following .Every Electrical engineer must have read and under stood these codes for safety reasons.

i) IS:3043-1987 - Code of Practice for Earthing (first revision)

ii) Indian Electricity Rules - 1956 (latest edition)

iii) National Electrical Code - 1985 of Bureau of Indian Standards

iv) IEEE Guide for safety in a. c. substation grounding. No. ANSI/IEEE Standard 80- 1986.