Best MFT to avoid RCD uplift?

[remedial]

just wondering if anyone can recommend an MFT that doesn't suffer (much) from RCD uplift? my megger 1710 is definitely not on the list

 

[Pete999]

What in Heaven is an RCD uplift??????????

 

[Silly Sausage]

Loop Impedance Testing: Have We Seen The End of Uplift? - https://professional-electrician.com/features/the-end-of-uplift/

I'd never heard of it before as well!

 

[Pete999]

Loop Impedance Testing: Have We Seen The End of Uplift? - https://professional-electrician.com/features/the-end-of-uplift/

I'd never heard of it before as well!

Well I never did, whatever next?? a complete new 18th MFT ro fork out for, with an uplift button?

 

[shaun1]

In the article above, it gives an example of an RCD adding an impedence of 0.5ohms to the circuit. Surely then that is part of the total loop impedance and should be included in the result, rather than being identified and subtracted? Or does it only appear to add that impedance to the test current, and behaves differently when a fault current is applied?

 

[Pete999]

In the article above, it gives an example of an RCD adding an impedence of 0.5ohms to the circuit. Surely then that is part of the total loop impedance and should be included in the result, rather than being identified and subtracted? Or does it only appear to add that impedance to the test current, and behaves differently when a fault current is applied?

Dunno shaun

 

[Charlie_]

At last an end to troublesome uplift!!
Hallelujah!
What could the answer be, oh yes the author of the thread happens to also sell the solution

I think rather than pay for a new tester, I might just carry out a loop test on both sides of the RCD

 

[davesparks]

What in Heaven is an RCD uplift??????????

It's just a word to describe the odd way that some RCDs can appear to increase the earth fault loop impedance of a circuit, usually as a result of the way an anti trip test is carried out.

In my experience the problem varies between RCD manufacturers as well as between different test meters.

 

[davesparks]

In the article above, it gives an example of an RCD adding an impedence of 0.5ohms to the circuit. Surely then that is part of the total loop impedance and should be included in the result, rather than being identified and subtracted? Or does it only appear to add that impedance to the test current, and behaves differently when a fault current is applied?

Quite often it only appears to add impedance to anti trip type tests.

 

[Risteard]

Megger MFT 1741 defeats RCD uplift.

 

[NDG Elecs]

At last an end to troublesome uplift!!
Hallelujah!
What could the answer be, oh yes the author of the thread happens to also sell the solution

I think rather than pay for a new tester, I might just carry out a loop test on both sides of the RCD

Megger are basically implying that their previous MFTs with lo current loop testing are not up to scratch then surely......???!!! Maybe I will ask for a part refund on the cost of my Megger due to them selling me an item that is slightly 'duff'.....

 

[Charlie_]

Megger are basically implying that their previous MFTs with lo current loop testing are not up to scratch then surely......???!!! Maybe I will ask for a part refund on the cost of my Megger due to them selling me an item that is slightly 'duff'.....

And they have known about this problem for years but didn’t bother mentioning it till now.
Not all RCDs just some and not all of the time, so they must have details of the ones that cause problems? That information would be very useful

 

[Charlie_]

Megger MFT 1741 defeats RCD uplift.

Your version of rock, paper, scissors?

 

[Wilko]

Being on the sick list and bored, I did a little science experiment, using a desktop TNCS, a new Wylex B32 DP RCBO (with Type A RCD characteristic) and my KT65 MFT.
The average results I got were less than 0.02 Ohms uplift through the device. This surprised me in that I’ve seen 0.1 - 0.2 on a couple of real circuits that I’d done the alternate method hi current test. The DC continuity test gave 0.00 Ohms across the device. As I’d expected, the new RCBO passed the 6 RCD tests and had 24mA trip on ramp test.
So I’m thinking - either some RCDs are more prone to this problem than others - or - my test was rubbish.

 

[telectrix]

think i've posted this before, ages ago. went to a call where BG had refused to connect boiler. Zs was well over 100 according to his socket tester. checked with MFT and got 352 ohms. thought maybe a useless rod, but when I checked the supply , it was TNC-S. Ze measured at 0.2 ohms. when I tried reading on the load side of the upfront RCD I got 349 ohms. that's more uplift than Katie Price. It was one of the old type RCCBs, lever switch on front, forget make now. may have been MEM,