Ieee 81

Status
Not open for further replies.
I

inspector 102

Senior Member
Location
Northern Indiana
Have contractor describing this standard for grounding test with megger. I have never seen this test done and am interested in seeing the results. Can anyone share the requirements guidelines with me so I have some idea what to look for. They are looking for maximum 3 ohm reading. Thanks
 
inspector 102 said:
Have contractor describing this standard for grounding test with megger. I have never seen this test done and am interested in seeing the results. Can anyone share the requirements guidelines with me so I have some idea what to look for. They are looking for maximum 3 ohm reading. Thanks
Click to expand...


IEEE 81 Measuring Earth Resistivity, Ground Impedance....​



I do not believe traditional Megger is ever involved in any of the described methods.​

 
Right, you dont use a megger for this test, however the actual meter does look like a megger with 500Ft long leads.

You need a fall of potential test set, involves driving current and potential test rods for true earth measurements.

Before the other guys jump in here and say the value dosent matter, why 3 ohms? Whats the application?
 
My apologies, the specs state that each grounding point shall be tested with a megger test. It then goes on to state "Perform test by the 2-point method in accordance with Section 9.03 of IEEE 81". What should I expect to see with this type of test. The facility is silicone manufacturing with alot of mixing and batching of material. The entire facility has a ground loop of #3 copper around the entrie building, cad welded at each metal column and supplemented at each column with a 3/4" ground rod at each column.
 
inspector 102 said:
My apologies, the specs state that each grounding point shall be tested with a megger test. It then goes on to state "Perform test by the 2-point method in accordance with Section 9.03 of IEEE 81". What should I expect to see with this type of test. The facility is silicone manufacturing with alot of mixing and batching of material. The entire facility has a ground loop of #3 copper around the entrie building, cad welded at each metal column and supplemented at each column with a 3/4" ground rod at each column.
Click to expand...

That must be either an older or a newer standard as my 1983 Standard states:





8.2.1.1 Two-Point Method (Ammeter-Volt-meter Method)​








In this method the total resistance of the unknown and an auxiliary ground is measured. The resistance of the auxiliary ground is presumed to be negligible in comparison with the resistance of the unknown ground, and the measured value in ohms is called the resistance of the unknown ground.​





The usual application of this method is to determine the resistance of a single rod-driven ground near a residence that also has a common municipal water supply system that uses metal pipe without insulating joints. The water pipe is the auxiliary ground and its ground resistance is assumed to be in the order of 1W and must be low in relation to the permissible driven ground maximum resistance which is usually in the order of 25 W.





Obviously, this method is subject to large errors for low-valued driven grounds but is very useful and adequate where a ​
go, no-go, type of test is all that is required.​





The most common testing method for industrial facilities, such as you describe, is the fall-of-potential method.​






 
Last edited:
inspector 102 said:
My apologies, the specs state that each grounding point shall be tested with a megger test. It then goes on to state "Perform test by the 2-point method in accordance with Section 9.03 of IEEE 81". What should I expect to see with this type of test. The facility is silicone manufacturing with alot of mixing and batching of material. The entire facility has a ground loop of #3 copper around the entrie building, cad welded at each metal column and supplemented at each column with a 3/4" ground rod at each column.
Click to expand...
You need to get clarification of the poorly written spec. The term "megger" generally refers to an insulation resistance tester and is used to measure very high resistances, not low ground resistances. A ground resistance tester as manufactured by Megger, can be used for a two-point resistance test per IEEE Std 81.

Is there a low impedance ground such as a metal water pipe system or a connection to the utility multigrounded neutral on site that you can use as an auxiliary ground?

This test would not be suitable for the whole ground loop, but might be for a rough measurement of individual ground rods if there is a contract requrement that each rod be lower than some value like 25 ohms. The question then would be, what do you do if the resistance of the individual rod is greater than this?
 
Since this is basically new to me, I have stated in my plan review that I want to be present for this test. I will post what the procedures where and the results when it get done and hopefully everything will make more sense. Thanks for the tips.
 
Basically you want them to provide you a test report with a graph on it showing a plateau region, typically a test is performed at 52%, 62%, and 72% of the distance to "Z"

A good quick read is "Getting down to Earth" available (free) on the megger website
 
Status
Not open for further replies.
Top