Fall-of-Potential vs. Clamp-on Ground Testing
Fall-of-Potential vs. Clamp-on Ground Testing
(OP)
Reference thread:
thread238-231298: Fall of Potential Testing in an industrial plant
Good morning all,
I wanted to get everyone's experience/opinion on using a clamp on meter instead of the traditional fall-of-potential test for ground testing. One of the general contractors is asking for a waiver to our current specs which state a fall-of-potential test shall be used for ground testing. They say that because pavement is already poured in the area and there is heavy work traffic (welding, other electrical testing etc.) a f-o-p test will be cost prohibitive as compared to using the clamp on meter.
The GC referenced this paper..
http://w ww.aemc.co m/techinfo /appnotes/ Ground_Res istance_Te sters/APP- Ground-Com parisonofT esters.pdf
But I cannot find any reference to a clamp on ground test in IEEE 81 or IEEE 142.
What are your thoughts on the clamp on meter vs fall-of-potential? Will either one give satisfactory results? Is the clamp on method recognized (by IEEE or other governing body) as an acceptable alternative to a fall-of-potential test?
Thanks in advance,
Andrew
thread238-231298: Fall of Potential Testing in an industrial plant
Good morning all,
I wanted to get everyone's experience/opinion on using a clamp on meter instead of the traditional fall-of-potential test for ground testing. One of the general contractors is asking for a waiver to our current specs which state a fall-of-potential test shall be used for ground testing. They say that because pavement is already poured in the area and there is heavy work traffic (welding, other electrical testing etc.) a f-o-p test will be cost prohibitive as compared to using the clamp on meter.
The GC referenced this paper..
http://w
But I cannot find any reference to a clamp on ground test in IEEE 81 or IEEE 142.
What are your thoughts on the clamp on meter vs fall-of-potential? Will either one give satisfactory results? Is the clamp on method recognized (by IEEE or other governing body) as an acceptable alternative to a fall-of-potential test?
Thanks in advance,
Andrew






RE: Fall-of-Potential vs. Clamp-on Ground Testing
RE: Fall-of-Potential vs. Clamp-on Ground Testing
RE: Fall-of-Potential vs. Clamp-on Ground Testing
Stakeless or Clamp–on method
Advantages
Test is quick and easy.
No disconnection of the ground rod from the system.
No probes need to be driven / cables connected
Measurement includes the bonding and overall connection resistance.
Measures true RMS leakage current flow through the system.
Limitations
Effective only in situations with multiple grounds in parallel (pole grounds).
Cannot be used on isolated grounds (no return path)
Not applicable for installation checks / commissioning new sites
Cannot be used if an alternate lower resistance return exists not involving the soil
– Cellular towers
– Substations
Subject to influence if another part of the ground system is in "resistance area":
– If there is another part of the ground system in the "resistance area" of the electrode under test, the result will be lower than the true resistance of the electrode – this could lead to a false sense of security.
Requires a good return path:
– Poor return path may give high readings.
Connection must be on the correct part of the loop for the electrode under test:
– Requires thorough understanding of the system.
– Wrong connection can give a faulty result.
Susceptible to noise from nearby substations and transformers (no reading).
There is no built–in proof for the method – results must be accepted on "faith".
RE: Fall-of-Potential vs. Clamp-on Ground Testing
For thise interested, I just received an email from an AEMC Instruments Application Engineer stating:
"IEEE is preparing a draft recognizing the clamp on used for ground resistance testing. It will be released in their next publication."
RE: Fall-of-Potential vs. Clamp-on Ground Testing
RE: Fall-of-Potential vs. Clamp-on Ground Testing
I once reviewed a test report of over 35 individual ground rods (no connections to any rods when tests were performed) where a clamp on tester was used with outstanding results!
You have to be at least 10% smarter then the equipment your using.
RE: Fall-of-Potential vs. Clamp-on Ground Testing
RE: Fall-of-Potential vs. Clamp-on Ground Testing
There are certain circumstances where it comes in quite handy. Telephone poles, railroad catanary towers, multiple small grids, etc. Providing they are electrically connected and spaced in a fashion that suits the clamp on method.
RE: Fall-of-Potential vs. Clamp-on Ground Testing