Get a set of decent leads from Kewtech to replace the Megger ones. Get a cotton bud and some switch cleaner and clean out the crud from the 4mm sockets on the back of the MFT and try again using the Kewtech leads on each instrument.

Hope this helps and let me know how you get on?

JP

It would be interesting to see if the readings are still varied with the new cable/leads and used on a calcard?

https://calcards.co.uk/

Sergio Fernandez said:

It would be interesting to see if the readings are still varied

The readings don't have to be the same between 3 instruments of the same model ... in fact it would be more unusual (although not wholly unknown) for the readings to be exactly the same.

A Cal Card (or resistance box etc.) wouldn't be of much help in respect of low-Zs loop test either.

Sergio Fernandez said:

It would be interesting to see if the readings are still varied

The readings don't have to be the same between 3 instruments of the same model ... in fact it would be more unusual (although not wholly unknown) for the readings to be exactly the same.

A Cal Card (or resistance box etc.) wouldn't be of much help in respect of low-Zs loop test either.

they wont be the same, but they may become more closely bunched. The 0.7 ohm cluster is almost spread over the full official spec - should be 5% +/- 5 digits, so 0.7 +-0.035+.05 or any where between 0.7+/-0.085  covers 0.615 to 0.785, while the measured spread is .77-.64 or 130 miliohms

The spread on the lower readings is almost the same, with the newer '71 unit reading about 180 milliohms below the higher of the others - which to me says systematic error, like leads.

Mike