HIGH Ze and Zs problems

[c.boy]

Hi all
changed a consumer unit today all circuits protected by rcbos.
Done all the usual tests, all good until i came to my Ze and Zs, its a TNC-S system.when testing ze my readings varied from 0.49 to 0.72.Iam NOT OUT IN THE MIDDLE OF THE WOODS!!I then procedeed to the Zs to see if i was getting a reasonable reading compared to my r1,r2, but when i tried to test zs the rcbo for the circuit under test kept tripping,sockets ,lights,heating e.t.c???? i have checked all the rcbos, no earth leakage and all trip within time!! my ? is, is there a problem on the supply side where the earth is maybe breaking down?? or is my brand new all signing and dancing meggar goosed???.

And this is not flats either!!!

Thanks

 

[trev]

As far as the high Ze goes I'd contact the DNO, it's their earth facility and therefore their problem, as regards the RCBOs tripping under tests, did you have your trip lock on?

 

[c.boy]

i have a new meggar 1720 and this has the no trip function brother!! done this a few times with my new tester and all readings were sound!!

 

[Deleted member 9648]

I've had the no trip function on my megger take out RCBO's on occasion...TBH as long as all other tests are satisfactory I just accept thats the way it is and calculate...Lifes to short.
Presumably you are doing the Ze on the high current setting?...in which case check it against another meter,and if still dodgy contact the DNO.

 

[c.boy]

It was the tester pal, Mr Megger has some ???s to answer too!!! thanks tho!!

 

[adslev]

Put the live probe on the earth terminal and the earth probe on the live terminal, should stop the tripping, has happened with me on different makes of RCBO's, Dorman Smith RCBO's are the worst my Megger1730 wont function properly with these at all!!

 

[MarkieSparkie]

There is a known issue no-trip testing on the Megger 17xx range with certain RCDs and RCBOs, particularly Wylex NSB and NSBS for NH boards. Megger are working on a firmware update to resolve this issue. Contact Megger Technical Department for further assistance.
http://www.electriciansforums.net/e...9285-megger-mft-1730-calculating-r1-r2-2.html

 

[Edd]

my 1730 trips RCBO's most time's,, bugs the hell out of me. I end up calculating zs from r1 r2 readings.. will look into this firmware update...

 

[Fusionsparks]

I'm surprised to hear this issue has still not been resolved. This top end piece of equipment has clearly been released before being thoroughly field tested!

I had to send two of these 1730 units back. Not due to them causing RCBO's or RCD's to trip during Zs tests but due to the fluctuation in readings whilst performing Zs tests. Also on none RCD protected circuits the readings taken on the hi current loop tests were always greater than those taken with no trip setting at the same point which I found disconcerting. As I performed the same test at the same points with another brand of MFT and got barely any fluctuation between hi current and no trip measurements.

It would be interesting to know what firmware version is installed on the suspect units mentioned? As I've read else where that the latest 17xx MFT's have firmware version 1.07. Has this fixed either of the issues above?

It would be useful (for anyone who has the ear of Megger) if the latest firmware version was clearly listed on the website detailing it's bug fixes if any.

 

[Deleted member 9648]

I have found the 2 wire no trip test very unreliable...my megger went back and was returned as OK. Megger stated that all Zs readings under 0.2 ohms are likely to be unreliable,but I have found all no trip tests are unreliable. Now I tend to do a couple or 3 tests on each point and if they are ballpark,good enough.If they are a bit random...(most likely!)...I take the average of 3 tests. All of which is a pain when each no trip test takes 15-20 seconds.....I've said it on here before,and still think the same...Meggers no trip ELI testers are not fit for the purpose.