Megger MFT1845 Application Note

APPLICATION NOTE
New "Confidence Meter"
adaptive loop impedance meter.

Applications:

Use in the initial verification / periodic inspection of low voltage fixed wiring installations and temporary
installations.
Also, testing after repair or modification of LV systems, ensuring continued compliance of disconnection
times for MCBs / RCDs providing fault and additional protection.
For measurement of earth loop impedance values and prospective earth fault current (PEFC) on phase
to earth circuits in single and three-phase systems where protection by an RCD or RCBO prevents the
use of a two wire high current loop impedance test.
Use where electrical noise affects the repeatability of measured values to the extent where it is difficult or
impossible to get a reliable loop impedance value, or where a significant number of repeated
measurements are required to provide a reasonable average.

Locations:

Any low voltage installation downstream of any RCD or RCBO devices that could trip if a standard
two-wire high current loop test were applied.

MFT1741/1845 new features:

The new Confidence Meter has been enabled on the three-wire loop impedance measurement mode
(3Lo) of the Megger MFT1741 and MFT1845. This replaces the existing 3-wire loop technology, offering
the following benefits:
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In use:

The 3Lo measurement should be chosen only where testing through an RCD or RCBO is required.
Connection of the MFT1741 or MFT1845 is made to the phase, neutral and earth conductors using either
the standard mains plug test lead or a three-wire test lead.
Pressing the TEST button will perform a safety check to ensure no hazardous earth conditions exist. The
test sequence will then measure the earth loop impedance of the circuit and display an initial value within
a four second window.
Megger Ltd, Dover, United Kingdom
Sales office: 01304 502 101,
Technical support: 01304 502 120,
New Confidence Meter adaptive measurement
Graphical representation of measurement 'quality' using the analogue arc
Stable, repeatable loop test result on noisy circuits
Reduced need for multiple testing from variable results
The ability to test through 10 mA RCDs and RCBOs
Option for testing 30 mA Type B RCDs without the risk of tripping
uksales@megger.com
uksupport@megger.com
www.megger.com
MFT1741/MFT1845 Confidence Meter
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