Best MFT to avoid RCD uplift?

[PEG]

I had to purchase a new Ouija 1751,to overcome the problems with ghost resistance.

 

[telectrix]

posted on another thread, this solves it at no cost with any MFT.

 

[Gavin John Hyde]

There is an ongoing argument at the moment about manufacturers both those who make rcds/rcbos and mfts as they all have there own interpretation of the standards and regs...
The ECA came out with a cracker recently when they said we only need to record the type ac trip times on the schedule of test results and not type a, b etc...
Likewise lewden said their rcbos work with the standard but mfts cant test them!
Megger just pleased ignorance and came back with something about the mft having a wide range ...
Seems everybody is doing their own thing. Not sharing info due to proprietary tech etc and everybody is confused

 

[telectrix]

my megger 1721 will test all types. just a setting to set for each. even my old (2008) 1553 can be set for AC or A types.

 

[Mikegh]

posted on another thread, this solves it at no cost with any MFT.
View attachment 90960

What do you do with the result as it's bypassing the uplift

 

[telectrix]

uplift may affect the test reading/s but have no effect when 240V is shoved into the circuit.

 

[24EMan]

What do you do with the result as it's bypassing the uplift

That is the point of testing the loop path without the RCD in the circuit. Connect the Line and PE at the extremity of the circuit and measure the earth fault loop from supply side of the RCD and open MCB of the circuit using a 2wire high current test which won't then trip the RCD and take out other circuits. Apparantly the uplift showing up in the MFT measurement is due to the way it carries out the low current test. It is not actually impedance in the earth fault loop at all. So the true Zs is Ze + (R1+R2) and uplift is purely a product inductance within the RCD being picked up by the way the MFT conducts a low current test. Of course another way of getting to the true measured Zs of a particular circuit is to measure the 'uplift' by taking a Zs reading on either side of the RCD and substracting this from the measured Zs at the extremity of that circuit.
Megger say they now have now overcome the effect of uplift in their newer 1741 MFT by employing a different 3 wire lo current test process in the design. Anyone here had the opportunity to compare test results from a 1741 and other models, or between different MFTs ?

 

[Mikegh]

I see , I wasn't quite getting the point that the uplift was a phantom resistance

I have never came across the issue, I'm using an older 3 wire loop tester , I dunno

 

[richy3333]

If you want a different tester just avoid Megger ? we use Metrel and have no issues with testing