Ze Reading.

[Engineer54]

OK i'm with you now!! lol!!

Not sure about the newer Megger MFT's, I know some MFT's require 3 wire connections and other units 2 wire. So i'll let others here advise on that one!! lol!!

 

[brman]

I have a fluke 1652 and generally have not noticed any problem.

However i was at a job a couple of weeks ago which was TNCS and I got 0.19 testing Line to Neutral (a 2 wire test on the fluke) and about 0.3 testing Line to PE (a 3 wire test).
I though there was something dodgy about the earth to the cutout so I tested at the cutout itself. So the tester neutral and PE wires were both connected to the combined N-PE terminal at the cutout.
I still got the different readings. I then went back to the CU and tested L-N and L-PE but both using the 2 wire test and they both gave the same results. (i.e. about 0.19 each)

I've haven't seen this before and it could be that I had a nulling problem (the fluke requires the leads to be nulled for Zs, unlike the meggers I think) but it did appear that the 3 wire L-PE test was getting confused! It might be something similar to what hutch has seen?

 

[oldtimer]

Well that explains everything you have a 1720 LOL

 

[hutch6447]

Why whats wrong with Megger 1720 seem decent to me.

 

[oldtimer]

Why whats wrong with Megger 1720 seem decent to me.

Well from what I am reading on the forum there is a few problems with them plus speaking to a couple of local guys wha are saying they are loosing confidence it them and want their old 1552 back.

PS I have a 1553 in a Fluke carry case

 

[hutch6447]

Yeah think brman has it right with machine getting confused with 3 wire test keep it to 2 wire testing and its fine.

 

[Guitarist]

Mate, I have a 1730 and know exactly what your problem is. L-N is the high current test which you should always do for all your PSCC and Ze testing (as there is no RCD to trip). L-PE is the no-trip setting and will always give a higher and inaccurate reading when using 2-wire. ALWAYS use 3-wire testing when using no-trip setting for RCD protected circuits and your readings won't be far out.

 

[hutch6447]

Cheers mate thanks for reply, just so I have got what you said when testing Ze, PFC you should have 2 wire test and always use the L-N.

When you test at the plug sockets to get your measure Zs do a 3 wire test, would a 2 wire test measuring Zs be better L-PE & L-N though.

 

[hutch6447]

Yes mate thanks for your reply fully understood what you mean Happy Days cheers mate.

 

[Guitarist]

Btw, I have spoken to Megger about making the appropriate limitations of the 1700 testing clearer. I have been assured that my concerns will be passed on to the people who write the manuals.
If they told me from the start "Do not use the 2-wire no trip unless absolutely necessary as the readings will not be accurate", it would have saved me a lot of hassle!

 

[oldtimer]

Btw, I have spoken to Megger about making the appropriate limitations of the 1700 testing clearer. I have been assured that my concerns will be passed on to the people who write the manuals.
If they told me from the start "Do not use the 2-wire no trip unless absolutely necessary as the readings will not be accurate", it would have saved me a lot of hassle!

So whats the point of the 2 wire no trip if the reading is not accurate the reason I mention this is megger sold this meter on the basis that you could do a Zs at a light switch instead of a light point I also got hold of a megger rep and said but we are told to check Zs at the light the reply was yes but this can save time and money now it turns out you will not get an accurate reading ?? if this was me I would measure at both the switch and light point just to see how much it was out

 

[Guitarist]

So whats the point of the 2 wire no trip if the reading is not accurate the reason I mention this is megger sold this meter on the basis that you could do a Zs at a light switch instead of a light point I also got hold of a megger rep and said but we are told to check Zs at the light the reply was yes but this can save time and money now it turns out you will not get an accurate reading ?? if this was me I would measure at both the switch and light point just to see how much it was out

That was exactly my point mate. When I put this to megger I was told that as it's a "no-trip" reading then there must be an RCD in circuit, therefore an accurate reading isn't essential as we have a few hundred ohms to play with where RCD's are employed.
I did explain that we need an accurate reading, regardless of that.

 

[oldtimer]

That was exactly my point mate. When I put this to megger I was told that as it's a "no-trip" reading then there must be an RCD in circuit, therefore an accurate reading isn't essential as we have a few hundred ohms to play with where RCD's are employed.
I did explain that we need an accurate reading, regardless of that.

What a mess Megger has got themselves in it seems that most of these "odd" Ze or PFC readings are generated by the 1700 series dont get me wrong I am not haveing a pop at Megger i have a 1553 (in a Fluke carry case) but if it was to blow up today the 1700 would be the last tester I would go for then again maybe Megger are taking the Microsoft approuch ie get it out there and let them field test it then we will fix it.

Maybe Megger should get themselves off the bench and out to the site with the guys who are having these problems

 

[Guitarist]

I have always been a Megger man and I believe that they make great kit. My real disappointment this time has been how laid back they have been about the issues I have had. Now that I have finally had a response explaining the limitations of the various tests, I can get on with confidence. As I said, if only they had included something in the literature then they could have saved me a lot of hassle.
Let's hope that they do indeed do something about it now so that others don't have the trouble so many of us already have.