When loop testing on a quiet circuit, the MFT1741 quickly returns a provisional reading and, at the start of the loop test, an arc is displayed. This very rapidly diminishes to a single element, indicating that the user can be highly confident of the result. This process is usually much faster than the standard test time of 15 seconds. On quiet circuits the final result is typically available within eight seconds.
On starting the test the complete arc is shown displaying a lack of confidence in the reading.
The arc diminishes until only one element remains showing high confidence in the result.
As confidence in the reading increases, the arc shrinks unless there is additional electrical noise.
The MFT1741 confidently reports the full result.
On very noisy circuits the tester displays a reading as the arc gradually shrinks. The result can be taken while the meter is in this ‘less confident’ phase but, given time, the arc will diminish to the single element, high confidence state. If additional noise is detected while the arc is diminishing, it will expand again, indicating increased uncertainty, before reducing to a single element.
For three-wire loop impedance measurements using this new technology, the results delivered by the MFT1741 are unaffected by the impedance of the RCD or RCBO in the circuit. Measurements are guaranteed not to trip the RCD or RCBO, except occasionally in the case of the rarely used 30 mA Type B devices. For these, Megger provides a Type B loop test option. The MFT1741 can also be used to carry out non-trip loop tests on circuits protected with 10 mA RCDs, as used in schools and other special locations.
In addition to its ground-breaking loop test capabilities, the MFT1741 offers all of the facilities needed to test electrical installations in line with the requirements of the IET Wiring Regulations, as well as valuable additional functionality such as the earth electrode resistance measurement.
As well as three-wire non-trip loop impedance testing, the MFT1741 offers two-wire testing, which is invaluable when tests must be carried out at locations where no neutral connection is available. High-current testing which delivers the fastest possible results for circuits that are not protected by an RCD or RCBO is also available.
Other key benefits of Megger’s new MFT1741 multifunction installation tester include insulation test voltages from 100 V to 1,000 V, automatic and manual RCD test options, fast continuity checking, frequency measurement and true RMS voltage measurement. Current can be measured using the optional clamp.
When used with appropriate accessories, the MFT1741 offers a choice of two-pole, three-pole, stakeless and ART (attached rod technique) methods for measuring earth electrode resistance. And for work on three-phase systems, this versatile instrument supports testing of three-phase RCDs even when no neutral connection is available; phase sequence detection; phase-to-phase loop testing at 415 V; and determination of prospective short-circuit current (PSCC) up to 20 kA. An important aid to efficiency is the large capacity internal storage for test results, complemented by wireless downloading to Bluetooth-enabled laptops.
Megger’s new top-of-the-range MFT1741 multifunction installation tester features rugged construction to ensure long life even in tough working conditions. The instrument has IP54 rated protection against the ingress of dust and water, making it extremely robust and reliable.
To find out more about Loop impedance testing with the MFT1741