'Double-barrelled' ground test

December 2000 Maintenance, Test & Measurement, Calibration

Many electrical tests, and the required instrumentation, complement each other. What one test does not reveal, another will. Spescom MeasureGraph believes that one should not be satisfied with guesswork or negative evidence. "Look around the fringes of your application to see if there is more than a single designated test can tell. The benefits can pay off!"

An interesting example is the use of AVO International's DCM300E earth leakage clamp meter together with any megger ground tester. The DCM300E conveniently clamps over a ground rod or conductor, and within seconds, digitally indicates the presence of any current flowing to ground. True, there should not be any, but it is surprising how often there is. Unbalanced electrical systems can send a leakage current of anywhere from a few milliamps to several amps, more or less constantly, to earth via the ground wires and rods.

Obviously, the test operator wants to protect himself from any unpleasant surprises caused by contacting several amps of leakage current unaware. The earth leakage clamp meter, clamped safely around the rod or conductor, senses field influence without actual contact and warns the operator before any physical contact is made with the grounding system. The benefits do not end there. The biggest advantage is protection from unjust recriminations when power quality problems (eg nuisance tripping) persist after adequate grounding has been installed. At best, the operator may be revealing a costly and dangerous condition that had not been suspected, and becomes a hero!

This one-two combination doubles both the faultfinder's protection and capabilities...and it is easy. The DCM300E fits in a shirt pocket and is user-friendly. Its range significantly surpasses that of an ordinary clamp-on... measuring down to as little as 0,01 mA to detect small leakage currents, which may be symptomatic of large power quality problems, and up to 300 A for more routine measurements. Its analog bar graph observes the time dynamics of current flow, a critical function in isolating the source of a problem.

Spescom MeasureGraph (AVO Sales)

Trevor Leong

(011) 266 1644

Previous issues containing AVO articles indicated Spescom MeasureGraph's general contact number. Readers please note that Trevor Leong is the designated contact for all of Spescom MeasureGraph's AVO sales. SA I&C apologises for any inconvenience.

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