Earth Resistance

The earth resistance as stipulated in standards is 1.0 ohm.This is sufficient to ensure operation of the earth fault relays.10% of the setting for E/F relays is sufficient to pick up the earth faults.

In the case of HRC fuses also the case is same.Due to low earth resistance there are heavy circulating zero sequence currents in the affected phase leading to the fusing of the HRC fuse of the affected phase.

In your case the earth resisance of 0.9 ohm is quite good to ensure safety of the electronic equipments/PLC/DCS etc.As you have conjectured 0.3 ohms is uncalled for and you are being fooled by your contractor.Further it is not essential to touch the water table for reducing the earth resistance.

Regarding faulty measurement/recording it is anybody's guess.It is difficult to comment upon.

At 0.9 Ohm you are already where you need to be. Depth is not the issue, it is contact surface area. If your contractor has not yet bonded the rebar in the building slab, or has not suggested simply driving two more grounding rods spaced at least their length away from the initial system, then he's just asking for an expensive change order.

By the way, there is nothing "wrong" with a deep earth system, and it would be very stable, just unecessary. The very length of the bare conductor reaching all the way down to an earth electrode at that depth would give you most of the extra contact that helps lower the resistance. You get similar "extra" contact (and slightly lower resistance, with less drop-off over time) by following the standard procedure of many contractors in the U.S. by making a triangle of additional shallow rods and exotherm-weld them together to the common GEC system...which, of course, is already bonded to the grounded metal elements of the building structure...

0.9 ohm of earth resistance is quite low. But if it is required to bring the earth resistance still lower to about 0.3 ohm the following options can be considered too rather than driving the earth stake to 80 feet to touch the water table. If you have steel structures in the vicinity bond the steel structures to earth grid this will increase the conducting path for the earth fault. Also you can go for 3-meter stake driven in to earth within earth pits with about 1 meter of conducting material like bentonyte. This will considerably bring down the earth resistance.

Be very very very careful adding additional earth stakes. There are two primary reasons for this. The first is that if have a loop of wire in a fluctuating magnetic field you have a generator. The earths magnetic field will fluctuate due to many things like transformers, ferrous items moving through it etc. The result is you and up with an induced current between the two stakes and this can induce noise on your earth. A similar thing happens if you connect the shielding of a cable to earth at both ends.

The second problem is more of a safety issue. If you have a lightning strike nearby the current will dissipate radially outwards from the point of contact. As a result any two points that are different distances from the strike point will have a different potential and the voltage difference can be many thousands of volts per meter. If you have 2 earth stakes a couple of meters apart then you can end up with enormous potential between them. The results can be devastating, and you could end up with a fire or earth that no longer works.

WooHoo! Free energy. I'm gonna drive 2 stakes in the ground and hook up my water heater to it. But with such enormous potential, maybe I need a bigger load. I'll also wire it to a big fan and point that at an old windmill. Which will pump water into a reservoir so a waterwheel can generate electricity to run a big flashlight which shines on a solar panel. Then I'll sell that power to 'the man'. If I use 2 different materials for the steaks(like ribeye and T-bone) the system should act like a battery. slo