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MFT1700 and MFT1800 series notice

Through our programme of continuous improvement, we wish to draw your attention to loop impedance testing on very high earth resistances. This notice covers the MFT1700, 1800 and 1701 series multifunction testers from Megger Instruments Limited.

Measurement affected: 3-wire non-trip loop impedance test.

In the very unlikely situation that a 3-wire loop impedance test is applied to a circuit of between 3300 Ω to 100,000 Ω to earth, there is a possibility that the voltage appearing on the CPC could exceed 50V. Although this lasts for less than half a second, this may be momentarily experienced by someone touching exposed bonded metalwork during the test.

This condition will not arise if the earthing and bonding has been verified as acceptable prior to performing a 3-wire earth loop impedance test.

Our advice to customers.

We consider the likelihood of this situation arising to be extremely rare and Megger has no record of any occurrence of this condition in the lifetime of this product range.

Instruments will be automatically updated when returned for routine calibration or repair, or customers can call Megger Limited for a Returns Authorisation number and return their MFT as below:


Megger Service and Repairs: 

Tel: +44 (0) 1304 502243

Megger can provide a courier service.

The Returns Authorisation (RA) number must be visible on the external packaging.


Return address if using alternative courier:

Megger Service and Repairs

Archcliffe Road, Dover, Kent. CT17 9TP


If customers are concerned about this condition, performing an RCD test on the circuit prior to the loop impedance test will alert the operator to any high resistance condition. This only affects the 3-wire non-trip loop impedance test. All other tests including other loop impedance tests are unaffected.

MFT1700 and MFT1800 series firmware updates V2
MFT1700 and MFT1800 series firmware updates V1