EarthPit electrode vs Earthpit Grid vs Earthpit EQ/ST

That is a task for a qualified Electrician. The test information needs to be gathered before energisation is sanctioned so as to achieve a high level of confidence that the circuit protective devices will operate on a fault occurring.

i want to know whether earthpit without any connected st/eq and earthpit resistance with connected st/eq will give resistance value same or different value.s

Then ask the qualified Electrician who is carrying out the test. This individual will be able to carry out the disconnection and report on the findings.

Perhaps just give some link to the standard methods for this person if you already know one. He is perhaps learning and is just cautious and worried as he is experimenting. He perhaps may end up in frying out his house.

PeterT:

The Earth system usually meant for protection so no great amount of current should flow into it and is there a way to find or track the place where such fault has actually occurred?

I have seen some sparking poles and I think there must be some way to find out where such thing is happening for quick maintenance or to prevent further damage. Similar thing may happen in sparks inside the house to the Earthed structure.

On your first comment, a very useful reference from a practical standpoint regarding grounding is the booklet "Getting Down to Earth" from the AVO / Megger® company. It used to be available from their web site, but I have not explored their download and support area lately.

As to the second, I would think that there would be something like the AFCI (arc fault circuit interrupter) technology or PD (partial discharge) that could be applied to find arcing faults on distribution lines such as caused by downed wires, tree branches, small animals, etc. However, I suspect the cost of adding that to the distribution infrastructure is prohibitive when you consider the many miles and branches of lines out there. It is a lot cheaper to wait until the customer calls in to complain that the lights are out, and then send a serviceman.

Many of the newer digital protective relays do have fault locating capability that will tell you how far down the line the fault occurred that caused them to trip.

That booklet did not show up at Megger.com, but I Goggled it and found it at tequipment.net.

I took a short course on grounding and bonding and passed the test to fulfill the required CEU's last year, but I don't work in the field much anymore, so I like to have things like this handy to be sure I am doing it right or to recognize when I need more qualified help. Thanks for the info! -- JHF

Measure pit resistance with Clamp type meter.

For earth pits connected with load or earth grid, it is better to measure the resistance of individual pit with the help of clamp type earth pit resistance meter.

Resistance values can be taken at any desired point, either for individual pit or for bunch of pits.

First of all, I agree with SWSlack and PeterT: only a qualified electrician has to execute the test.

However, if you want to know "theoretically" what you have to test, my opinion is as following:

NEC art.250 does not state what you have to test except one individual electrode [25 ohm maximum if it will be a single electrode] to check if a supplementary electrode is necessary [Art.250.56].

If it is not in the scope of NEC domain [see art. 90.2 Scope.] for a substation [or power station] purpose, for instance, I think IEEE 81 will be indicated to follow.

The earth resistivity has to be tested before any underground work is done-foundations, grounding grid and other [if it is possible in two opposite seasons-higher and lower temperature].

Mr Qadir,

Earth pit resistance should be measured with the grid ( connected to structures and equipment ) and without both. As standards define data of individual pits and grid data.

Pits normally should have a resistance of 5-7 ohms ( latest OISD 244 is trying to define it at 2 ohms ) while the grid resistance must be less than 1 ohm. This is for power earthing. In case of lightning earthing pit may have a resistance of n*10 ohms and grid less than 10 Ohms. But if gerids are interconnected as per standards the stringent of all the standards for individual gridds will apply. i.e ig lightning and power earthing grids are mixed the pit shall need to have 5-6 ohms and grid less than 1 ohm. This is for Indian standards.
Iyengar.

OISD STANDARD-244 is an Indian standard for STORAGE AND HANDLING OF PETROLEUM PRODUCTS AT DEPOTS AND TERMINALS. I don't think the o.p. is referring to this domain. However, and I don't see any reference to the grounding in this standard. Did you? May be you intend to say IS : 3043 Indian CODE OF PRACTICE FOR EARTHING.In this standard -the same as in other as BS 7430 ,VDE 141,IEEE-142,IEEE 80 an so on- what is important it is only touch potential [dependent on the fault clearance time] or touch and step potential [IEEE-80] and no limitation of the grounding resistance value.So, if at the beginning the measured maximum touch potential for the maximum grounding fault current will be suitable then what you have to check if the total resistance stays in the limits as designed, from time to time. If it is not happened, you have to check the grid connection to the foundation grounding and then -if it is possible, since the modern grid cable connections are welded -permitting higher temperature for the same cross section area-you have to disconnect each grounding pit from the grid and test the electrode resistance and compare with the initial value.

YES. OISD ( DRAFT) 244 IS FOR STORAGE AND HANDLING OF PETROLEUM PRODUCTS.... BUT THIS TALKS OF EARTH PIT RESISTANCE OF 2 OHMS. MIGHT BE WHEN IT GETS INTO A STANDARD - BIS 3043 meant for EARTHING may get modified. AS of now 244 is in draft stage only. Elsewhere the pit resistance is quoted to have 5-7 ohms. One question which comes to mind is that when all other parameters of earth pit design are firmed up and only earth quality is the variable factopr how come a fixed or below value can be obtained.??? coke breeze might have to be replaced by chemicals.