Reducing earth resistance and pipe earthing

Methods to reduce earth resistance

1. Increase electrode length/depth: a longer rod or pipe driven deeper reaches moist soil of lower resistivity.
2. Use several electrodes in parallel: spaced at least about twice their length apart, so their resistance areas do not overlap.
3. Chemical treatment of soil: fill the pit with alternate layers of charcoal and common salt, or use bentonite or a chemical earthing compound, which holds moisture and adds ions.
4. Keep the soil moist: provide a watering funnel/pipe and water the pit regularly, mainly in the dry season.
5. Increase electrode size: use a larger plate or a bigger diameter pipe (a smaller effect than length).
6. Use a counterpoise or earth mat: buried strips or a grid in substations lower the total resistance.
7. Choose a good location: moist, low-lying clay soil away from rock and sandy areas.

Pipe earthing (as per IS 3043 practice)

   Funnel with wire mesh
        ___
        \ /     Cement concrete chamber
   _____| |__________  ← ground level
  |  [ ]---- GI earth wire to equipment
  |  | |  (via 12.7 mm GI pipe)
  |  | |                 Pit filled with
  |  | |  ##  alternate layers of
  |  | |  ..  charcoal and salt
  |  | |  ##  (about 15 cm around pipe)
  |  | |  ..
  |  |o|  ← 38 mm dia GI pipe, 2.5 m long,
  |  |o|    with 12 mm holes along length
  |  \_/  ← tapered bottom end
  |________________
   about 3.75 m deep below ground

Process:

1. Pipe: a galvanised iron (GI) pipe of 38 mm internal diameter and 2.5 m length (longer in dry soil) is used. It has 12 mm holes drilled along its length so water can reach the soil, and its lower end is tapered for driving.
2. Pit: a pit is dug and the pipe is placed vertically so that its bottom end reaches about 3.75 m below ground in normal soil (deeper in dry soil).
3. Backfill: the space around the pipe, about 15 cm wide, is filled with alternate layers of charcoal and salt. This keeps the soil moist and conductive.
4. Watering: a 19 mm pipe with a funnel and wire mesh is connected to the top of the earth pipe so water can be poured in during dry weather.
5. Earth lead: the earth wire (GI wire or strip) is connected to the pipe top by a reducing socket/clamp, and taken to the equipment through a 12.7 mm GI pipe for protection, at least 60 cm below ground.
6. Chamber: a cement-concrete chamber with a cast-iron cover is built at the top for inspection and watering.
7. Testing: the earth resistance is measured with an earth tester (fall-of-potential method). It should normally be below about 1–5 Ω depending on the installation; if higher, more pipes are added in parallel or the soil is treated further.

Pipe earthing is cheaper and easier to keep moist than plate earthing and is the most common type for buildings and small installations.