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thiagarajan sriram
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Join Date: Feb 2011
Posts: 9

Earth Resistance

12/14/2011 3:41 AM

We have made two earth pits for our DCS system and 4 earth pits for our power supply panels etc. All are in a row.Distance between each earth pit is 5 mtrs and the earth pits are 2 mtrs away from the building.When we checked Before connecting earth flats to the earth pits we observed continuity between all the earth pits. In that area the earth resistance was 0.15 ohms.If the earth resistance is low is it possible to get continuity between earth pits eventhough there is no physical connection between the pits(i.e.electrodes).Pl clarify.

T.Sriram
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PWSlack
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#1

Re: earth resistance

12/14/2011 4:36 AM

Of course. The measurement is revealing that fact.

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roopesh
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Join Date: Oct 2011
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#2

Re: earth resistance

12/14/2011 5:48 AM

Hi thiagarajan sriram./

Mr.PW's reply is enough ah?

Got it ah?
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electricalexpert65
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#3

Re: earth resistance

12/14/2011 7:21 AM

Be happy, rather than complaining. Not many people would get an earth resistance of less than one Ohm, without inter-connecting the pits. You must be having a wonderful soil over there.
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redfred
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#4
In reply to #3

Re: earth resistance

12/14/2011 8:50 AM

Maybe yes, maybe no. Resistance is a parameter between two locations. When measuring earthing resistance, it is very easy to accidentally measure cable resistance instead of the ground resistance. An earthing resistance of about 1/8 Ohms is possible but this is such an exceptionally low resistance claimed that it makes me wonder if this is real.

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brzk
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#5

Re: Earth Resistance

12/15/2011 1:08 AM

Good morning,

Earthing resistance varies every times all through the year, depending on your climate. Your value of 0.15 ohms is accidentally good. Next time (i-e, within 6 monthes) it will be less good, etc. Except if your earthing pits are collected through a trench, correctly erected, full of a good sand, etc. and all your rods connected through a bus bar of, for instance, a bare copper of 100 sqmm. Except in that case, earthing continuity through the soil is, consequently, not guaranteed. You must, at first connect all your rods, make a new check of that value and then be able to evaluate the new connections. For memory, for electrical circuits, you need only one ohm of value, if your switchgear is in metal and your power cables of pvc.

Best wishes and merry christmas to everybody, BRZK.

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Wal
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#6
In reply to #5

Re: Earth Resistance

12/15/2011 6:20 AM

Agree with most of your points BRZK. Bonding is critical through a serviceable connection. You don't really mean sand do you?

Questions for the OP. Did you measure the resistance to earth of each "pit"? Describe the soil type if you can. Are there other interred earthing elements at this site?

Although the achieved resistance to earth is important so too is the dimensioning of the system. eg a couple of knitting needles and some fuse wire might also give low ohm readings but do not constitute a good earth. Please describe the "pits".

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nesubra
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#7

Re: Earth Resistance

12/16/2011 6:12 AM

Exceptionally low value.What type of soil is there.Like other posts state u need to check the resistance during peak summer when soil will be dry.It is better interconnect all earth pits as planned.

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Wal
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#8

Re: Earth Resistance

12/16/2011 8:06 PM

Soil resistivity, theoretically, should not change with the weather.

This paper explores some of the practicalities of the issue:

http://www.cder.dz/download/upec-7.pdf

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