Faulty Test Kit????

[t4msy]

I'm hoping theres someone here that can give me some advice. I have a seaward combi compact tester which i put in for calibration. I have been told there is a fault on the tester as when it runs an earth fault loop impedance test it only ever records 0.67 ohms. I found this very strange as i have been using the tester regularly and have numerous installation certificates on which none of the recorded values are 0.67ohms. They actually vary from 0.15 to 1.5ohms. I also know they are approximately correct as i also use the calculation method for Zs.

I was rather concerened when the man testing my machine asked if i could take the manual with me as he had no documentation on it. Yet they are supposed to be seaward approved. He didn't even know how to set the machine to carry out the test.

I have just picked the tester up and refused to pay the bill (£75) as in my opinion they are not competant to have been calibrating the machine.
I have the calibration certificate which states on 7 different applied test values for L-PE (0.57-100ohms) the result was 0.67ohms on all 6 then 1ohm result for 100ohm applied.

The strange thing is i have just run the loop test across my PME supply at home (straight across the tails) to find Ze and got a value of 0.18ohms which i would think is about right. I then borrowed a friends robin loop tester and that recorded 0.19ohms.

Is it possible they wern't testing my machine properly? Can anyone suggest a way in which i can check the EFLI readings myself.
I already check the continuity meter and ins resistance with resistors. But cannot check the EFLI or RCD trip times myself.

 

[mapj1]

testing ELFI, at least partly,
If you have some low value (high current- suggest wirewound aluclad type or similar - see RS catalogue) you can add these in serties with your 0.18 ohm supply, and see the reading rise to 1ohm plus 0.18, 2 ohms plus 0.18 or whatever. If you are paranoid, do the sam with your mates Robin and compare notes.
The resistors must be good for the test current (the type that trip RCDs oten use 10A, so dont use little ones - spend a fiver at RS/farnell or CPC
and get the right thing.)

Sounds like they were inept and gave you someone else's result sheet.
I'd ask for a refund if your tests are OK, and keep 'triangulating' against your mates one and the resistors periodically. (Test an RCD with both testeers to if you can, see if the average of 5 trip times tally with both machines)


cheers M.

http://cpc.farnell.com/jsp/endecaSearch/searchPage2.jsp?Ntt=aluclad&Nty=1&N=401&Ntk=gensearch
which are these
http://www.farnell.com/datasheets/910.pdf
are the sort of resistors I'd use... perhaps screwed into a suitable box and marked up 'calibration transfer standard' Don't use an earthed metal box though if you are doing ELFI measurements - it will become live during the tests - the tests are short, so heating is not an issue, and an insulating plastic box will be fine. For a quick test, just use them dangling, but keep fingers clear of the terminal ends.