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Morning all,

having a bit of a fun time with my tester at the moment. Bear with me as I'm still in training.
Ive got a Dilog 9083p. I know it's not regarded as the best tester out there but like I said, I'm just starting out.

The problem I have is this. Ive tested Ze at the board and all is good. tested my r1+r2 and all is good. when it comes to testing Zs on the circut it comes up really high almost double. for example my sockets came out at 1.5 ohms where as the calculated figure using Ze+(r1+r2) comes out at about 0.7 ohms.

The instructor then says.. now test it with the fluke. And I got a figure of 0.68 ohms. I tried the same test with a metrel and a Megger and they all came up high. only the fluke was anything near accurate. what causes this and is there any way around it? I know theres nothing wrong with doing the calculations but if I didnt have another tester to use, it would leave me wondering if there is a problem with the RCD or breaker if that makes sense
 
Morning all,

having a bit of a fun time with my tester at the moment. Bear with me as I'm still in training.
Ive got a Dilog 9083p. I know it's not regarded as the best tester out there but like I said, I'm just starting out.

The problem I have is this. Ive tested Ze at the board and all is good. tested my r1+r2 and all is good. when it comes to testing Zs on the circut it comes up really high almost double. for example my sockets came out at 1.5 ohms where as the calculated figure using Ze+(r1+r2) comes out at about 0.7 ohms.

The instructor then says.. now test it with the fluke. And I got a figure of 0.68 ohms. I tried the same test with a metrel and a Megger and they all came up high. only the fluke was anything near accurate. what causes this and is there any way around it? I know theres nothing wrong with doing the calculations but if I didnt have another tester to use, it would leave me wondering if there is a problem with the RCD or breaker if that makes sense

is this on a test rig or real life installation?

sometimes the test rigs will give different results with different testers due to the way they have been configured.
i.e. extra resistors etc hidden at back of rig to simulate different scenarios.

have you asked the instructor why you are getting different results with different testers?
 
it's in a training centre but you wire your own circuits and then test them. so we do Showers, cookers, ring SWA to a garage and various lightind circuits. there's no faults built into this one although I have that coming with the 3 phase part next week.
I asked the instuctor and he just says "thats because Dilog is rubbish" I asked if Metrel and Megger were also rubbish in that case and he didnt have a reply. when I showed him what I'd found with the other testers he just giggled and said, just use the Fluke in future. lol
 
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it's in a training centre but you wire your own circuits and then test them. so we do Showers, cookers, ring SWA to a garage and various lightind circuits. there's no faults built into this one although I have that coming with the 3 phase part next week.
I asked the instuctor and he just says "thats because Dilog is sh$t" I asked if Metrel and Megger were also sh$t in that case and he didnt have a reply. when I showed him what I'd found with the other testers he just giggled and said, just use the Fluke in future. lol

I have also seen, in places where more than one person is testing at the same time. 1 tester interfering with another and getting some strange test results.
 
I have also seen, in places where more than one person is testing at the same time. 1 tester interfering with another and getting some strange test results.
yeah could be that I suppose... just leaves me doubting my tester. I know we should always do the calulation to check against the measured but it seems a bit pointless if you cant trust the measured reading. If I did then every single circuit would fail on max Zs :D
 
Quoted from the July 2018 Megger article...
"RCDs and RCBOs usually incorporate a tiny transformer with a winding connected in series with the live conductor, and another winding in series with the neutral conductor. This transformer detects the difference between the currents in the live and neutral conductors, which indicates the presence of earth leakage."

IMO, Megger of all people should check their terminology is accurate to the latest regs.
 
this illustrates my problem exactly. looking at the megger site they now reckon uplift can add as much as 1 ohm1?

Yeah, that's a huge difference. And makes the measurement using that method largely pointless.
 
I'd be taking resistance readings across the RCD and measuring Zs at the RCD on the load terminals and the supply terminals. As a matter of curiosity and education.
I have honestly never seen readings skewed this far from predicted (calculated) values. Only small amounts attributable to the inaccuracy of a low current Zs test.
 
I'd be taking resistance readings across the RCD and measuring Zs at the RCD on the load terminals and the supply terminals. As a matter of curiosity and education.
I have honestly never seen readings skewed this far from predicted (calculated) values. Only small amounts attributable to the inaccuracy of a low current Zs test.
yep, I tried 3 meters, all gave roughly the same degree of error. the only decent one was the fluke.
Ive got my practical part of my 2391 - 52 in October so will be fun trying to educate the examiner on RCD uplift lol
 
I asked the instuctor and he just says "thats because Dilog is rubbish" I asked if Metrel and Megger were also rubbish in that case and he didnt have a reply. when I showed him what I'd found with the other testers he just giggled and said, just use the Fluke in future. lol

I think it is the instructor who is rubbish, not the tester. I would ask him to explain this properly or else make a formal complaint about his incompetence. You've no doubt paid a lot of money for this course so it's only fair to be getting good quality training rather than childish giggling.
 
I think it is the instructor who is rubbish, not the tester. I would ask him to explain this properly or else make a formal complaint about his incompetence. You've no doubt paid a lot of money for this course so it's only fair to be getting good quality training rather than childish giggling.

yeah it was a bit rediculous. I went home thinking I needed to buy another meter (not that they say we have to use our own) the next day I decided to do a test using the other meters and it was only the Fluke that came anywhere close. all of their meters are in a pretty sorry state and was a bit surprsed as mine had just passed calibration and had a brand new set of leads. Ive got the department head teaching us next week so I'll have words with him and see what he says
 
yeah it was a bit rediculous. I went home thinking I needed to buy another meter (not that they say we have to use our own) the next day I decided to do a test using the other meters and it was only the Fluke that came anywhere close. all of their meters are in a pretty sorry state and was a bit surprsed as mine had just passed calibration and had a brand new set of leads. Ive got the department head teaching us next week so I'll have words with him and see what he says

Different test meter manufacturers use different technology to achieve a 'no trip' loop test so they have different levels of success at measuring through different brands of protective device.
Low current or no trip loop tests are always a compromise between possible inaccuracy and convenience/speed of testing. I would hope that they taught you the difference between a standard (sometimes called high current) test and an anti trip test, along with the limitations of each when you learned the theory of how the tests work and why they are done the way they are.

Ask the tutors to demonstrate testing an RCD protected circuit using a high current test, this is often known as the alternative Zs test method.
The basic method is you fit a L to E short at the far end of the (isolated at the rcd) circuit and test between the line in and line out terminals of the RCD.
I often use this method when testing stage lighting installations to remove the dimmer from the circuit without disconnecting anything.
 
Historically, loop testers have struggled with "RCD uplift" and older models are (in general, though not always) more prone than newer ones. Having used a number of testers from different manufactuers over the past 5 years or so, my experience is as follows:

  • Older Dilogs (9093) = affected
  • Newer Dilogs (9118, not sure about 9110) = not affected
  • Older Meggers (1710/20/30) = affected
  • Newer Meggers (only tried the 1741) = not affected
  • Flukes (old and new) = not affected
  • Kewtech (only tried KT63, not tried KT64/65 but suspect the same) = not affected

So historically, Fluke and Kewtech have always been good, whereas others are now catching up.

No idea of Metrel or some of the other brands, sorry.

"Your mileage may vary." :)
 

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