Earth mats obtain the earth resistance with a large contact area. The earth mats consists of a number of flat strips laid in the form of a grid. The grid is placed in a trench which is about 75 cms deep. The flats are made of mild steel and are of 75 x 8 mm size.
The flats are welded to one another. The low resistance is achieved by the increased contact area this method provides.
The earth resistance should ideally be less than 1 ohm. The resistance value should be periodically checked and recorded.