New ground rod test with a meggar

[CB2]

How do you test a new ground rod with what I think is a standard Meggar(three wires, red, black, and green)? This is a new installation and I need 25 Ohm or less.

Thanks for the help
CB2

 

[CB2]

Sorry, the "ground rod" is installed in the ground.

 

[electricpete]

I don't know the answer. You may have more luck in the power engineering forum.

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[busbar]

See discussion and links in
thread238-34416
thread238-11119

 

[jbartos]

Suggestion: References:
1. Donald G. Fink "Standard Handbook for Electrical Engineers," 13th Edition, McGraw-Hill, Inc., 1993,
Section 38 Measuring Ground Rod Resistance on page 17-38
There are three major methods being applied:
1. Triangulation or three-point method
2. Ratio Method
3. Fall-of-Potential Method (ConEd in NYC uses)
2. IEEE Std 142-1991 IEEE Recommended Practice for Grounding of Industrial and Commercial Power Systems,
Section: 4.4.2 Methods for Measuring
Reference 1 Ditto

 

[ScottyUK]

CB2,

A 'megger' is the generic name for an insulation resistance tester, which can deliver a high voltage at a very low current in order to measure insulation between conductors and between conductor and earth. The early ones were made by a company called Megger, and the name has stuck.

Ground impedance testing uses a different bit of kit called an earth resistance tester or some variation on those words. Off the top of my head, European manufacturers include:

Chavin Arnoux
Seaward
AVO-Megger

Have a look through Google, searching for the following keywords

Earth Resistance Instrument

Here's one page to get you started:

http://www.avointl.com/uk/products/

and look in the Building Wiring / Contractor column.





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Start each new day with a smile.

Get it over with.

 

[jbartos]

Suggestion: If there are two test ground rod electrodes and tested ground rod electrode, the megger must have three leads. The instruction should be available from the megger manufacturer.

 

[DanDel]

Both a Megger and a Ground Test Set can have three leads. The three leads on the Megger are usually marked '+', 'G', and '-'. The 'G' is for the Guard terminal, which is used to remove losses from one component(such as the secondary winding of a transformer) when you are trying to get the losses to another component, such as ground, from the third componment (primary winding). The Megger will usually have an adjustable voltage control, as well as a range selector for the meter. The meter ranges will be in the kilo-, mega-, giga-, and/or tera-ohm range.
The leads on the Ground Test Set (and there may even be four) represent the connections for the three(or four)-point ground rod tests. The meter ranges will read in ohms, maybe down to the hundreths or thousands, but certainly no higher than hundreds.
First, make sure that you have the right instrument. What is it that you have?

 

[panelman]

We use a standard earth loop (PSC) tester, this will give you the loop back to the transformer.

Don't forget to disconnect the service earth (if fitted) and a can of water is usefull

 

[jbartos]

Suggestion: Visit

http://www.usace.army.mil/publications/armytm/tm5-683/c-14.pdf

for ground resistance test methods

 

[Dopler]

To measure ground resistance (25 ohms or less) you need another system, not with a Megger (insulation resistance tester), but with a ground resistance tester (3 or 4 rod method)or with a clamp on tester.

http://www.mytoolstore.com/ideal/ide05-01.html

 

[porf]

Got to following URL for an excellent description of a ground resistance tester and methods:

http://www.aemc.com/techinfo/

then click on Ground Resistance Tester