You ask: I’ve noticed that if I repeat an earth loop impedance test several times on the same circuit, the results sometimes vary a lot.
Why is this and how do I decide which of the results to record on the test certificate?
We answer: Electrical noise and harmonics in the circuit under test can affect the accuracy and repeatability of loop impedance measurements when these are carried out using no-trip test methods.
The noise and harmonics might be generated in the installation that’s being tested or they might come from other locations that share the same low-voltage supply. In either case, however, they’re virtually impossible to eliminate.
The solution is to carry out your loop impedance tests with Megger’s new MFT1741 multifunction installation tester. This uses adaptive loop impedance technology to deliver dependable results, even when noise and harmonics are present.
In addition, it has a unique ‘confidence meter’ display that shows when a stable and reliable result has been reached. With the MFT1741, deciding which measurement to put on the test certificate is never a problem, because it delivers a single result that you can rely on with confidence!
And, of course, this versatile new instrument offers all of the other facilities you’ll need for installation testing.
For more information visit: https://uk.megger.com