grounding & bonding test
- Thread starter cakre
- Start date
- Status
brian john
Senior Member
- Location
- Leesburg, VA
1. No NEC article.
2. What type of meter are you using to perform this test? Meter type makes a difference to your question.
2. What type of meter are you using to perform this test? Meter type makes a difference to your question.
zog
Senior Member
- Location
- Charlotte, NC
Clamp on meters have lots of limitations on when and how they are used. You can do a 3 pt, 4 pt, or slope methid with the fall of potential test set. There are many variables in ground testing, most people go through much training before buying a test set so they know what they are doing.
A good start is to download and read "Getting down to earth" from the megger website.
A good start is to download and read "Getting down to earth" from the megger website.
brian john
Senior Member
- Location
- Leesburg, VA
Most clamp on test I see have problems due to the location of the test and/or downstream grounds on the neutral/grounded conductor.
The 4-point test is generally utilized prior to designing a grounding system to determine the resistivity of the soil and the size of the ground system to achieve a specification.
The 3-point test is taken on the made electrode disconnected from the service (which is why the clamp on was designed). Typically you need to go a minimum of ten times the made electrode out to the farthest test probe . Then drive the second test probe at 10% increments and at 66% position. This is completed is several directions (3 or 4 complete test). The Curve that is derived from these test is reviewed and if the curve does not show you are outside the sphere of influence you redo the test at a greater distance.
In my expierence most folks do not want to go to this extent and drive one probe at 100" and second probe at 66' take a measurement and walk away.
for starters
http://www.aemc.com/techinfo/techworkbooks/ground_resistance_testers/950-WKBK-GROUND-WEB.pdf
The 4-point test is generally utilized prior to designing a grounding system to determine the resistivity of the soil and the size of the ground system to achieve a specification.
The 3-point test is taken on the made electrode disconnected from the service (which is why the clamp on was designed). Typically you need to go a minimum of ten times the made electrode out to the farthest test probe . Then drive the second test probe at 10% increments and at 66% position. This is completed is several directions (3 or 4 complete test). The Curve that is derived from these test is reviewed and if the curve does not show you are outside the sphere of influence you redo the test at a greater distance.
In my expierence most folks do not want to go to this extent and drive one probe at 100" and second probe at 66' take a measurement and walk away.
for starters
http://www.aemc.com/techinfo/techworkbooks/ground_resistance_testers/950-WKBK-GROUND-WEB.pdf
zog
Senior Member
- Location
- Charlotte, NC
brian john said:
You mean 62% right?
- Location
- Illinois
- Occupation
- retired electrician
Exactly what are you trying to check. The previous answers are about testing the ground resistance of the grounding electrode. Is that what you are doing?cakre said:
I am trying to take ground resistance on the each panel. I talk to my supervisor and i explain that i do not need to switch OFF the main breaker to take the readings with the clamp meter or with the 3 points metod but he insist on that that the main breaker need to be OFF and then i could proceed with the meassurement.but we have a problem. by the main panel.the generator over there if we shuted off we can not restarted by "X" reasons.
So mine MAIN QUESTION is: DO I NEED TO SHUT OFF THE MAIN BREAKER OR GENERATOR TO TAKE ACCURATE REDINGS WITH THE CLAMP METER OR 3 POINT METOD OR NOT.
Thanks for any answers and any concerns from your side gents.
So mine MAIN QUESTION is: DO I NEED TO SHUT OFF THE MAIN BREAKER OR GENERATOR TO TAKE ACCURATE REDINGS WITH THE CLAMP METER OR 3 POINT METOD OR NOT.
Thanks for any answers and any concerns from your side gents.
zog
Senior Member
- Location
- Charlotte, NC
cakre said:
Ground resistance on each panel? Are you looking to test the panel resiatance to ground? It sounds like what you really need to do is call a testing company or someone that knows what they are doing.
brian john
Senior Member
- Location
- Leesburg, VA
62%, but editing is at minimal setting and by time I saw my error time had passed. WE NEED LONGER EDITING access for dolts like me!
Oh the troubles we get in when we assume.
1. What is the purpose of the readings you want.
2. Is this an ground electrode to be tested or the resistance of the equipment ground for the distribution panels (ground bar and associated conductors).
If this is anything but the ground electrode neither test will serve you.
Oh the troubles we get in when we assume.
1. What is the purpose of the readings you want.
2. Is this an ground electrode to be tested or the resistance of the equipment ground for the distribution panels (ground bar and associated conductors).
If this is anything but the ground electrode neither test will serve you.
Last edited:
Yes (highly likely)cakre said:
As has been stated:
1. It is not in the NEC.
2. Know and understand the limitations of your test equipment. Read the test equipment manufacturer's literature. If there isn't sufficient information in the mfg literature, call the mfg eng dept.
3. Decide which measurement you want to take. (you have listed two completely different connections)
We don't know your system. We don't know the size of the system, number of panels, voltage levels, number and sizes of transformers, process equipment that could effect measurements ... the list continues. Is this an office building, industrial site, commercial, maybe even a house. We don't know what the system may have for currents on the ground system. We don't know what test equipment you have.
You have this information, we do not. We can not give you any more than general guidelines.
carl
- Location
- Bremerton, Washington
- Occupation
- Master Electrician
I suggest you read up on the two methods of testing.
The grounding electrode conductor (GEC) is not normally current carrying, unless there is a lighting or line surge.
for the three point fall of potential method, the GEC is disconnected from the electrode under test.
For the clamp on method, the grounding electrode must be connected to the electrical system.
Since you are not working in the panel, it may not be necessary to turn off the main. I don't know all the particulars, voltage, etc, thats why I say may.
See what the instructions for the testers say.
The grounding electrode conductor (GEC) is not normally current carrying, unless there is a lighting or line surge.
for the three point fall of potential method, the GEC is disconnected from the electrode under test.
For the clamp on method, the grounding electrode must be connected to the electrical system.
Since you are not working in the panel, it may not be necessary to turn off the main. I don't know all the particulars, voltage, etc, thats why I say may.
See what the instructions for the testers say.
Problem is the AEMC Clamp-On , and 3-Point Fall-Of-Potemtial Test cannot be done on the EGC in branch panels. Well the AEMC can be used in the Main Panel if clamped to the right cable like the MBJ or service grounded circuit conductor.cakre said:
To measure the impedance of the EGC back to the Main panel MBJ you have to apply a current between the EGC buss and the Nuetral buss in the branch panels, then read the voltage developed and convert to impedance. There is test equipment made to do this, I use a DLRO meter.
brian john
Senior Member
- Location
- Leesburg, VA
{quote]There is test equipment made to do this, I use a DLRO meter.
[/quote]
Do you normally spec this, as part of acceptance testing on your projects?
I see it asked for in hospital specs and ocassionally for telcom sites.
[/quote]
Do you normally spec this, as part of acceptance testing on your projects?
I see it asked for in hospital specs and ocassionally for telcom sites.
The problem, as noted by others, is that you would use a clamp-on ground resistance tester or a 3 points fall-of-potential ground test to measure the resistance of a ground rod. This is something you would do at the ground rod not at each panel. You could use a clamp-on type tester anywhere that the grounding electrode conductor is accessible, which might be at a panel. Thus all of the questions asking what you are actually testing.cakre said:
Assuming that you are measuring the resistance of a ground rod, you would not need to shut off the main breaker to take an accurate reading with a clamp-on type tester if you can find a point where the tester can safely be clamped around the rod or the lead to the rod without disconnecting the ground. To do a 3-point test, you have to disconnect the ground rod from the source neutral. If you do this without shutting off the power, then you will be operating without the grounding electrode connected. Unless the ground rod is a supplemental grounding electrode only, this would not be acceptable.
- Status