Re: GRN Testing: Clamp-on vs 3 Point
The 3point FOP is as accurate as the clamp on method, however, the clamp on will not give you accurate values on mutable or large ground systems as stated in the manufactures manual. The clamp on will give you false good values (low values 5 to 7 ohms) if not used properly.
The 3 point FOP is a valid IEEE method and the clamp on is not, so, you need to understand why the test is performed and the type of system you are measuring.