25 OHMS for grounding.

[GOZ]

Can anyone give me the code reference for the " 25 Ohms " rule?

 

[iwire]

250.54

 

[templdl]

To confirm that you have less that 25 ohms can be a bit challenging. You simply default to driving 2 ground rods and call it a day.

 

[GOZ]

250.54

Thank you

 

[GOZ]

To confirm that you have less that 25 ohms can be a bit challenging. You simply default to driving 2 ground rods and call it a day.

A little back ground. My plant has an annual Grounding test done. This year we used a different company. They go by NETA standards of .5 ohms in a point to point test as a pass and anything above .5 is a fail. Needless to say we have alot of fails.

Which standard is the standard i should follow?

 

[GoldDigger]

That sounds more like a bonding test than a grounding test.
If you want that low a point to point resistance you will have to use a metallic bond (wire or raceway), not just electrodes.
No ground electrode is that good!


Tapatalk...

 

[GOZ]

Here is the procedure they use.

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7. INSPECTION AND TEST PROCEDURES​

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7.13 Grounding Systems​

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* Optional​

Page 121​

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ANSI/NETA ATS-2013​

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1. Visual and Mechanical Inspection​

[/FONT]

1. Verify ground system is in compliance with drawings, specifications, and NFPA 70​

[FONT=TimesNewRoman,Italic]NationalElectrical Code Article 250.​

[/FONT]

2. Inspect physical and mechanical condition.3. Inspect bolted electrical connections for high resistance using one or more of the followingmethods:1. Use of low-resistance ohmmeter in accordance with Section 7.13.2.2. Verify tightness of accessible bolted electrical connections by calibrated torque-wrenchmethod in accordance with manufacturer?s published data or Table 100.12.4. Inspect anchorage.​

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2. Electrical Tests​

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1. Perform resistance measurements through bolted connections with a low-resistance ohmmeter,if applicable, in accordance with section 7.13.1.2. Perform fall-of-potential or alternative test in accordance with ANSI/IEEE 81 on the maingrounding electrode or system.3. Perform point-to-point tests to determine the resistance between the main grounding system andall major electrical equipment frames, system neutral, and derived neutral points.​

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3. Test Values3.1 Test Values ? Visual and Mechanical​

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1. Grounding system electrical and mechanical connections shall be free of corrosion. (7.13.1.2)2. Compare bolted connection resistance values to values of similar connections. Investigatevalues which deviate from those of similar bolted connections by more than 50 percent of thelowest value. (7.13.1.3.1)3. Bolt-torque levels shall be in accordance with manufacturer?s published data. In the absence of​

manufacturer?s published data, use Table 100.12. (7.13.1.3.2)

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7. INSPECTION AND TEST PROCEDURES​

[/FONT][FONT=TimesNewRoman,Bold]

7.13 Grounding Systems ([/FONT][FONT=TimesNewRoman,BoldItalic]continued[/FONT][FONT=TimesNewRoman,Bold])​

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* Optional​

Page 122​

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ANSI/NETA ATS-2013​

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3.2 Test Values ? Electrical​

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1. Compare bolted connection resistance values to values of similar connections. Investigatevalues which deviate from those of similar bolted connections by more than 50 percent of thelowest value.2. The resistance between the main grounding electrode and ground shall be no greater than fiveohms for large commercial or industrial systems and one ohm or less for generating ortransmission station grounds unless otherwise specified by the owner. (Reference ANSI/IEEEStandard 142)​

3. Investigate point-to-point resistance values that exceed 0.5 ohm.
[/FONT]

 

[GoldDigger]

The whole process assumes that there is a single Ground Electrode System (GES ) and that all of the electrodes in the system are metalically bonded together.
If this is properly done, the point to point resistances will be low because they do not depend on current flowing through the earth.
You could (should) have less than .5 ohms point to point even if you disconnected all of the electrodes from earth.
A connection only to an isolated ground rod does not provide a fault clearing path nor any significant degree of safety.

Tapatalk...

 

[GOZ]

The whole process assumes that there is a single Ground Electrode System (GES ) and that all of the electrodes in the system are metalically bonded together.
If this is properly done, the point to point resistances will be low because they do not depend on current flowing through the earth.
You could (should) have less than .5 ohms point to point even if you disconnected all of the electrodes from earth.
A connection only to an isolated ground rod does not provide a fault clearing path nor any significant degree of safety.

Tapatalk...

That was the switch to the light above my head. Thank you sir. Some times my brain over complicates.

 

[GoldDigger]

You are quite welcome. My brain does that too. Alternating with oversimplifying.

Tapatalk...

 

[templdl]

A little back ground. My plant has an annual Grounding test done. This year we used a different company. They go by NETA standards of .5 ohms in a point to point test as a pass and anything above .5 is a fail. Needless to say we have alot of fails.

This is the that I understand it:
Which standard is the standard i should follow?

I wasn' t aware that NETA had standards. It was my understanding that NETA was and organization that adopted standards that were accepted in the industry. If you are a member you have agreed to accept those standards yourself which provided a degree of consistency within NETA members. Hire those who a a member of NETA and you should be assured of a level of electrical testing.
But NETA only adopts standards, they don't magically set standards that debate from those that are already in place.
You really don't have to be a member of NETA to do standardized testing because the standards already exist.

 

[cowboyjwc]

One plant we did here wanted .1 ohm to ground and used chemical grounds at each steel column and cad welded them together and all sorts of stuff. Me? Once I had the Ufer and the cold water, I was good.

 

[zog]

I wasn' t aware that NETA had standards. It was my understanding that NETA was and organization that adopted standards that were accepted in the industry. If you are a member you have agreed to accept those standards yourself which provided a degree of consistency within NETA members. Hire those who a a member of NETA and you should be assured of a level of electrical testing.
But NETA only adopts standards, they don't magically set standards that debate from those that are already in place.
You really don't have to be a member of NETA to do standardized testing because the standards already exist.

Thats not true at all, NETA develops thier own standards, some of the specifications are derived from other references but they do develop them, review them, and audit them all the time. They have a standards review council in charge of the process. Since 1996 NETA acceptance and maintenence standards were adopted and recoginized by ANSI as a national standard.

 

[templdl]

Thats not true at all, NETA develops thier own standards, some of the specifications are derived from other references but they do develop them, review them, and audit them all the time. They have a standards review council in charge of the process. Since 1996 NETA acceptance and maintenence standards were adopted and recoginized by ANSI as a national standard.

Thanks for the clarification. So ANSI accepts NETA testing standards , the NETA standards being different than the ANSI standards and not visa versa, interesting. Then I'm to understand the NETA does develop its own testing standards apart from ANSI which are different/ in addition to the the existing NEMA and ANSI industry standards.
For clarification and my understanding is there an example where NETA has added a test that exceeds ANSI/NEMA standards than have been blessed/accepted as valid by the manufactures?
I would like to understand what services a NETA member provide in addition to a non NETA person who adheres to NEMA/ANSI standards as accepted and by manufacturers.

 

[zog]

Thanks for the clarification. So ANSI accepts NETA testing standards , the NETA standards being different than the ANSI standards and not visa versa, interesting. Then I'm to understand the NETA does develop its own testing standards apart from ANSI which are different/ in addition to the the existing NEMA and ANSI industry standards.

Close, NETA is an accredited standards developer for ANSI, ANSI does not develop any standards on thier own, they rely on organizations like NETA that are experts in that specific field. When it comes to power system equipment acceptance and maintanance procedures, the NETA standards ARE the ANSI standards. NEMA is for manufacturers, which you know.

For clarification and my understanding is there an example where NETA has added a test that exceeds ANSI/NEMA standards than have been blessed/accepted as valid by the manufactures?

Yes, happenes all the time as new technologies become available. The last major example was for MV cable testing, EPRI research in the 90's found out traditional DC hipot testing can damage service aged cables so new non destructive test methods were developed. Now VLF, PD, and Tan Delta are the 3 allowable tests. Not only did NETA/ANSI change the standards, so did IEEE and ICEA.

I would like to understand what services a NETA member provide in addition to a non NETA person who adheres to NEMA/ANSI standards as accepted and by manufacturers.

Nothing. However NETA does have requirements for the company that they will audit (Calibrated test equipment, technition training hours, safety, CTD's, etc...) and NETA techs are certified to 4 different levels (Another ANSI standard, very difficult proctored exams with many hours of training as a prerequisite). So chances are with a NETA certified company you have a higher quality tech and equipment but I have seen bad NETA companies and excellent non-NETA companies that just follow the standard.

 

[templdl]

Close, NETA is an accredited standards developer for ANSI, ANSI does not develop any standards on thier own, they rely on organizations like NETA that are experts in that specific field. When it comes to power system equipment acceptance and maintanance procedures, the NETA standards ARE the ANSI standards. NEMA, which you know.


Yes, happenes all the time as new technologies become available. The last major example was for MV cable testing, EPRI research in the 90's found out traditional DC hipot testing can damage service aged cables so new non destructive test methods were developed. Now VLF, PD, and Tan Delta are the 3 allowable tests. Not only did NETA/ANSI change the standards, so did IEEE and ICEA.

Nothing. However NETA does have requirements for the company that they will audit (Calibrated test equipment, technition training hours, safety, CTD's, etc...) and NETA techs are certified to 4 different levels (Another ANSI standard, very difficult proctored exams with many hours of training as a prerequisite). So chances are with a NETA certified company you have a higher quality tech and equipment but I have seen bad NETA companies and excellent non-NETA companies that just follow the standard.

Who is NETA a credited by by? Yes, there is a need for NETA as an organization which has standards of which their members are held accountable to. A company that commissions a NEMA member will be assured that there will be a given level of testing. But a non NETA member can provide the same thing if standard industrial testing as accepted by the industry are completed. By commitioning a NETA member the customer is more apt to be assured that all applicable test are conducted as I would understand.
As far as hipot testing and anything I have always been of the belief that when done multiple times it can be detrimental. Do it once. If done more than once can lead to a failure. If it doesn't fail on the first test wrap the cords up put the instruments away and go on to the next testing procedure.
I do like your last statement which I feel is the most important and that is to assure that the techs are more apt to be better educated and trained which I feel is lacking is out industry.

 

[zog]

Who is NETA a credited by by? Yes, there is a need for NETA as an organization which has standards of which their members are held accountable to. A company that commissions a NEMA member will be assured that there will be a given level of testing. But a non NETA member can provide the same thing if standard industrial testing as accepted by the industry are completed. By commitioning a NETA member the customer is more apt to be assured that all applicable test are conducted as I would understand.

Don't recall through whom, been awhile since I sat on the board.

As far as hipot testing and anything I have always been of the belief that when done multiple times it can be detrimental. Do it once. If done more than once can lead to a failure. If it doesn't fail on the first test wrap the cords up put the instruments away and go on to the next testing procedure.

In most equipment I would agree but MV cables are a little different, even one DC test can cause water tree propagation, most easily in XLPE cables. Thats why every MV cable testing standard out there all agree on not using a DC hipot on service aged cables.

I do like your last statement which I feel is the most important and that is to assure that the techs are more apt to be better educated and trained which I feel is lacking is out industry.

Yep, there are alot of posers out there, I deal with them daily. In fact I have a ABB LK 1600A breaker in the shop right now that was "remanufactured" by another company last year (They were lower bidder than I was), when we tore down the mech to individual parts (Normal scope) we found that the operating mech and other subassemblies were never fully disassembled and were re-plated as assemblies!! Looked pretty on the outside, interior parts were all rusted where the surfaces met.

The thing about NETA certification is that is does not travel with the tech, it is only obtained while working for a NETA accreditied company. Years ago I because the 22nd person to pass the level 4 exam in 40 years (Not many level 4 guys out there), when I left that company I lost that certification (Work for a non NETA company now) but I didn't lose any knowledge. I think Brian John was also NETA certified at some point, now with a non NETA company but still very knowledgeable.

 

[GoldDigger]

The thing about NETA certification is that is does not travel with the tech, it is only obtained while working for a NETA accreditied company. Years ago I because the 22nd person to pass the level 4 exam in 40 years (Not many level 4 guys out there), when I left that company I lost that certification (Work for a non NETA company now) but I didn't lose any knowledge. I think Brian John was also NETA certified at some point, now with a non NETA company but still very knowledgeable.

Does the company have to work their way up to having level 4 employees, or could you, if you wished, fairly easily renew your certification at the new company?

 

[zog]

Does the company have to work their way up to having level 4 employees, or could you, if you wished, fairly easily renew your certification at the new company?

I would have to sit for the level 2 and 3 exams first (And work for a NETA accreddited company). For level 4 you need 10 years experience in the testing industry and over 700 hours of documented training.

Here are the requirements for the exams.
http://www.netaworld.org/sites/default/files/public/documents/ett2010_profile_of_neta_technician.pdf

This is what it takes for a company to become NETA accreddited.

http://www.netaworld.org/sites/default/files/public/documents/becomingneta2011newlogo.pdf

 

[GoldDigger]

I would have to sit for the level 2 and 3 exams first (And work for a NETA accreddited company). For level 4 you need 10 years experience in the testing industry and over 700 hours of documented training.

Here are the requirements for the exams.
http://www.netaworld.org/sites/default/files/public/documents/ett2010_profile_of_neta_technician.pdf

This is what it takes for a company to become NETA accreddited.

http://www.netaworld.org/sites/default/files/public/documents/becomingneta2011newlogo.pdf

Thanks.