Ze test results

[butler26]

hi there

i got a loft conversion about 18 moths ago and had a TN-C-S PME system installed as i didnt have an earthing system in place any way i had a qualified electrian come out to test the installation of the loft . his result for the Ze was 0.21 ohms and his pfc was 1.1KA. im a trainee sparky and have just bought a metrel 1552 tester and thought i would do a Ze test but my result was 0.07 ohms and the pfc was 3.1 KA does anyone no why my results would be differnt from his .and i do no how to do a Ze By isolating the supply then removing the supplied earth and testing from the incoming side of the main swith at the cu

thanks

 

[m4tty]

Have you got that the right way round Andy?

Edit: are you deleting posts Zee lol

 

[Zeespark]

I know, I realised My mistake so deleted the post, I apologise for the nuisance caused to all.

AndyGuinness

---------- Post Auto-Merged at 17:34 ---------- Previous post was made at 17:33 ----------

Yes because it was wrong, I didn't read the question correctly, I only realised after I had posted, so deleted the post before I threw a spanner in the works.

AndyGuinness

 

[sparkytim]

? I find Ze normally lower then Zs (Zs = Ze +(R1 +R2))

Maybe the supply network has altererd in the last 18 months, not unusual for readings to change.

 

[butler26]

thanks for the reply i just thought that he may of made a mistake but you have answerd my question

 

[Evans Electric]

I wonder about my mind sometimes ......I thought you were a German sparks for a second , giving us ......" Ze test results" :coat :C

 

[Robin Spark]

Ok I am not familiar with Metrel testers as I have always used a fluke mft which allows you to toggle between L-E and L-N when doing EFLI tests. So just a thought are you measuring PEFC or PSSC as that might be a factor towards some of the differential in the reading, but it would depend on how far away the consumer unit is from the cutout.

 

[butler26]

Hi on my meter when doing a PEFC or PSCC you have to Test between L-E then between L-N as there is no toggle feature and the cu is right next to the cut out

 

[batty]

I will think you will find it all depends on the tester being used. Low current loop testers are not that accurate its the way they test. I have three and they would all give different readings when testing a ZE. I think the most accurate loop testers are the ones that put a 25 amp current down circuit for a very short period like the old Robin testers with d-lok.

 

[steptoe]

maybe they have actually gave you a PME system now, but when your spark tested it it was only TNCS ......

 

[Sidewinder]

Steps! ]

---------- Post Auto-Merged at 19:30 ---------- Previous post was made at 19:29 ----------

IF, this is a DNO network change, this is the reason I keep harping on about NOT using your measured figures!

You MUST contact the DNO for their values, and only IF they tell you to use the measured values, should you!!!

 

[gordy71]

Please explain sidewinder, why do u use the dnos figures? Surely if your tester is calibrated and the test result is satisfactory there is no probs? Its out of your control if they make changes, or have i got the wrong end of the stick?

 

[Sidewinder]

You must use DNO figures mate especially with BIG installs.

Take my local DNO, I have spoken to them, and not the jointers, the area engineers.

They limit PSCC & PEFC to 25kA, regardless of the Ze.

Thus you have to use this figure.

They do this by design of their network.

 

[apprentice87]

Hi all! Off you go one day and you do an installation and you measure the PSCC and PEFC, and you are a happy bunny that all is well, and that your overcurrent devices can break whatever the measured fault current might be.

Next week though, the nasty DNO go and build a nice shiny new substation, and right next door too!! All your design work has now gone out the window, you might as well not have bothered.

I would not say that this is "the DNO's problem" as it is up to you to design a safe system, that can handle reasonably foreseeable scenarios. As your nice new system might have a life span of some decades, it is more likely than not that the DNO will "reinforce" their network at some point. This needs to be taken into account, so use the DNO figures as Sidewinder has said!!! [Well, I would anyway!!!]

john..

 

[batty]

But there figures will be a maximum .8 for tns and .35 for tncs unless you are talking about heavy industrial stuff. I really cannot see why anybody will worry what may happen in the future you design your system to what is there at the time that is what the forms are for.

 

[Sidewinder]

Yes Batty they may be, however, they may not be.

Those values are just typical as quoted in 7671.

However, the DNO's also cap their PFC's

 

[batty]

Yes Batty they may be, however, they may not be.Those values are just typical as quoted in 7671.

However, the DNO's also cap their PFC's

But if I ring DNO tomorrow these will be the figures they quote they cannot know any different they may test when they install a supply but they will not record figures although some write it on meter board anyway surely any supply may alter slightly at any time of year.

 

[steptoe]

just hope you dont need a 40c in a TNS install. :slap

 

[NozSpark]

Haaaaaaa,,

Buggered before you even start:slap

 

[Sidewinder]

But if I ring DNO tomorrow these will be the figures they quote they cannot know any different they may test when they install a supply but they will not record figures although some write it on meter board anyway surely any supply may alter slightly at any time of year.

I just typed a huge reply and the site lost it sorry Batty I can't do this again.

Suffice to say this is not the situation.