Number of Earth Pits

Yes, there are rules for wiring up almost everything in a power distribution grid. These convoluted, arcane rules are your local wiring code. They change from location to location for a variety of reasons. Listen to your site engineer, licensed electrician, or electrical inspector how your installation should be done. There are lives at stake.

Yes. It is mandatory to provide 2 Earth Pits for the Neutral of the Transformer. For DG also 2 Earth Pits are to be provided. This I studied about 20 years back, and I do not remember the reason and I will try to refer my notes and post it.

DHAYANANDHAN.S

What is a "trafo" and a "DG"?

Trafo is TRANSFORMER, and DG IS Diesel Generator.

DHAYANANDHAN.S

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DHAYANANDHAN

Yes. It is mandatory to provide 2 Earth Pits for the Neutral of the Transformer. For DG also 2 Earth Pits are to be provided. This I studied about 20 years back, and I do not remember the reason and I will try to refer my notes and post

I am anxious to hear why you need 2 "Earth Pits". If they are installed the NEC requires they be bonded together. So why two?

Most projects having 63A or higher current rating motors propose double earthing. It may be by 8 swg wire or copper strip of 25x3 or 40x5 size. Having two separate pits ensures that if one pit is disconnected due to strip breakage, the other is operational.

VGA

Electric codes change to fit the experiences of the regions. Installers and designers that do not know which codes apply to their location should consult with someone who does know those rules. I'm certain that CR4 has individuals qualified, authorized and employed in identifying how may and distant multiple earth pits are required for a location. Only the OP knows the site of this installation. We cannot even tell the OP which codes should apply.

You should make sure the Safe conection And redundancy about de short circuit current for each source of energy. Other good practice is interconect both or each source ground grid. This are good practice for electrical installations and should be followed in order to match the local rules.

THEORITICALLY SPEAKING ONE NO EARTHING WILL DO, YOUR EARTH RESISTANCE MUST NOT INCREASE 1 OHM WITH THE PASSAGE OF TIME & VARIATION OF EARTH RESISTANCE IN DIFFERENT SEASON . BUT IN PRATICE THIS USUALLY DOES NOT HAPPENS. SO MORE THAN ONE EARTH PIT/POINT OF 3 MT DEEP IS RECOMMENDED.TO INCREASE THE RELIABILITY OF THE EARTHING SYSTEM WITH THE PASSAGE OF TIME & VARIATION OF EARTH RESISTIVITY DEPENDING UPON THE SEASON.I PERSONALY RECCOMEND 4 NO EARTHING PITS AT LEAST 3 MT DEEP- 2 FOR TRANSFORMER NUTRAL & 2 FOR TRANSFORMER BODY. REGARDING THE QUESTION OF DISTANCE BETWEEN EACH EARTH PIT IT MUST BE AT LEAST 3 METER APART, IF TOO NEAR TO EACH OTHER BOTH THE EARTH POINTS MAY START BEHAVING AS ONE SINGLE EARTH. THE ABOVE LOGIC ALSO APPLIES TO D.G SETS EARTHING.

Practice shows that theory is useless in predicting all possible fault modes. Earth pits installations primarily handle fault conditions. Proscribing any method without knowing anything about the terrain or application is at best foolish at worst criminal.

It is mandatory to seggregate the two systems.

Neutral earthing PITs are connected to main power system and is used for maintaining the neutral point

Equipment body are connected to separate set of PITs as they are safety aspects and any leakages to the equipment should be earthed.

Why Separate system:

In case the neural point voltage is not zero or there is unbalanced loading, we do not want to compromise on human life.

There are always redundant pair of PITs.

Hope queries are addressed.

I would request that please don't think of saving money every where, there are authorised professionals, who design considering techno commercial best solutions.

MANDATORY?According to what authority?Please give reference for this statement..it is in direct conflict with the National Electrical Code (USA)

See comment 7 above.

Have a nice day!

My only argument is that all grounds should be bonded together to provide an equipotential grounding point.I realize that in high voltage, high current situations, merely walking on the ground across a high resistance soil can create a voltage differential between left foot and right foot.Which is why a grounding grid is sometimes used, and the design of the grid itself is highly locality dependent,and local AHJ should be consulted.

I am sure everyone here is saying the same thing,because they all seem very knowledgeable and professional.The only problem seems to be semantics, not technicalities.

In that regard, I consider all respondents to be on equal ground (pardon the pun),and I am willing to accept misunderstandings that have occurred since the Tower of Babble.

My best wishes to all! Live well,live long, and find contentment.

Follow the electrical standard prevailing in the country of installation; were it in the UK, then BS7671 would apply, for example.

An important thing to remember is that 2 resistors in parallel will have a total resistance less than either one alone.I have seen cases where even residential installations require more than one ground rod,and that they be bonded using Thermite(cad bonding),no ground clamps. Imagine a 8ft ground rod with a sphere of soil surrounding it of 8ft.diameter.The second ground rod will need to be at least 8 feet away to get effective halving of the resistance by putting more soil in the ground path.

In very high resistance soils,chemicals are allowed to be poured around the rod(s) or (pit) to enhance conductivity.Some chemicals are magnesium sulfate, copper sulfate, and rock salt

Inspectors can tell if a ground rod has been shortened without digging,using a resistance tester from the rod to test rods located a measured distance away.

Rocky soil, like in mountains present their own problems,and sometimes an angled or horizontal burial is permitted.

It all depends on the soil type and is determined by local AHJ.

The NEC standard for ground rods is 25 Ohms.Two in parallel will give you 12.5 ohms,3 in parallel will give you 8.33 ohms if all resistances are equal.If only one of the resistances is lower,the combination will be even lower than that lowest resistor.