New LTW range of earth loop impedance testers now makes it possible to carry out two-wire loop tests with no risk of tripping 30mA RCDs, even in systems where electronic RCDs are used.
As well as saving time and eliminating the risk of incorrect connections, dependable two-wire testing is a major benefit in applications where the neutral is missing or inaccessible, such as light switches, systems with 110V centre-tapped supplies, and many types of luminaire.
All of the new testers are three-phase safe and are category IV 300V rated, making them suitable for use on supplies from 50V to 300V AC single phase, as well as on 440V three-phase installations.
To address electrical contractors’ requirements for easier loop testing, Megger has made a major investment in developing the innovative technology used in the new LTW testers.
Extensive use is made of new digital processing techniques to separate the test signal from the fundamental frequency of the supply, with a large number of results automatically averaged over the duration of the test.
This enables non-trip testing to be performed without DC injection, a technique which is, in any case proving ineffective with electronic RCDs.
The new LTW range includes four models, all of which normally complete their test sequence in ten seconds. If electrical noise is detected on the supply, however, the test is automatically extended to ensure that an accurate result is achieved.
The entry-level LTW315 provides all of the facilities needed for two-wire non-trip loop testing on supplies between 110V and 280V, while the LTW325 extends the voltage range to cover supplies between 50V and 440V, as well as adding facilities for displaying max Zs and R1+R2.
The LTW335 is functionally the same as the LTW325, but includes facilities for storing and downloading test results. All units provide PFC calculation as standard.
The resolution provided by the LTW315, LTW325 and LTW335 is 0.01 ohms but for applications where even more accurate results are needed – for example, to allow the accurate calculation of high prospective fault currents – Megger offers the LTW425.
This provides the same facilities as the LTW325, but has an enhanced resolution of 0.001 ohms, enabling a PFC calculation to 40kA.
All loop testers in Megger ’s new LTW range feature an IP54 weatherproof case, a backlit display, and built-in folding front cover, and all are supplied complete with standard test leads, a mains socket test lead and a calibration certificate.