Testing.

[EdwardCurrent]

Hello All,
I am trying to grasp the skills of testing and would appreciate some help please.
I am a tad worried about my meter, (traded the fluke in for a Metrel due to not having part p etc +I have just had it callibrated)

First results on a circuit where additions are required.

EFLI
3.2 ohms down to <.3 ohms ??? On a ring from the same s/o.

Confused I came home and checked my ring

1.1 and 1.7 from the same s/o.

It's the meter isn't it ???? please say yes.

Would the 'reading' be constant regardless of equipment being connected to the circuit ?
Thanks for any advice, and yes I know I need training but this is a nice place, with some very clever folk whom can help me along the way, and for that I thank them, very much.


Edward.

 

[securespark]

Eddy: I have Metrel Alphatek 61557. Yes,I find the readings can vary quite a bit, even when doing resistance tests. Sometimes I find after zeroing the leads that a further push of the button produces a non-zero reading. Anyone else had this??

I also find that No 10 test (soft EFLI test) gives a higher reading than No 7 test (EFLI w/o RCD).

However, that said, 3.odd Ohms & even 1.7 Ohms are too high for TN systems on a 32A device.

Can you give us a bit more to go on?

 

[EdwardCurrent]

Cheers for the reply SS.
I don't know what what to do to be honest, apart from having the meter re-calibrated .
Would my next step be to test the Ze?? before looking at the consumer side of things. Would this be a 'constant' reading ?
(Disonnected the earth from the main earthing bar, with the Mainswitch isolator 'OFF', and measure, 3 lead in the metrels case ?)

I do opologise

Ed

 

[ColJack]

yup, that's your Ze test..

don't forget to reconnect the earth BEFORE re-energising the installation...

how are you testing at the socket? plug in adapter?

in older sockets, the prongs inside the socket weaken over time and oxidise some, often giving higher readings than at the terminals on the back of it..

 

[tim west]

also time should be given between tests to allow internal components in the meter a chance to cool down and stabilise.

 

[bongos]

Recently when helping with a PIR we were using a plug in adapter on a Fluke. Different resistances were displayed between both s/o on the same double socket.

I was told this was probably because of cheap (and old) socket fronts. When we tested using the probes behind the s/o instead of the plug in adapter, the resistances were virtually the same at all points of the ring.

 

[ricicle]

And don't start testing as soon as the meter is brought in from a damp, cold van. Let it climatise to the room temperature before starting.
No-trip Zs tests are inaccurate anyway IMO.

 

[EdwardCurrent]

Thank you all very much for the help.

I returned to the installation today to carry out a Ze test.

I took my time between tests and managed to obtain a stabilized reading of .36-.39ohms. I understand that this value needs to be under .35ohms (TN-C-S system).
The house is right near the end of a road(line), where the other homes are mainly TT set-ups, but the owner in question had his supply changed some ten years ago. (< i don't know if this is relevant ).

Wouldn't this effect further testing, and should I contact the DNO and see if they can help ?

Thanks

Ed

 

[Spark123]

I'd see if I could borrow someone elses tester to check the Ze, if it is still above they you could call the DNO in, however you will end up red faced if he turns up with his ancient AVO efli tester and gets a lower reading (make sure they do it in isolation if they do come out).

 

[EdwardCurrent]

Many thanks.

I am very sorry but I failed to mention that there are 2 x C/U's at this property. . 'Earths' are connected via a block. I left the 2nd C/U connected to the block, but had the mainswitch off and the earth disconnected inside the c/u .

Is this correct please ???

Regards

Ed.

 

[Spark123]

No, isolate everything and disconnect the lead which goes into the MET from the DNO cutout. Test this lead with it not connected to anything else i.e. in isolation.

 

[Cremeegg]

As others have said - test Ze first - it will be pretty constant.

What type of earthing is it - if PME the DNO wont be bothered with such a marginally high reading. If TNS if looks OK.

Meters will give differing results in sockets and socket adaptors used infrequently. Have you a calibration checkbox? Reasonable ones on EBay for £20 or so. Helps you keep track of your meters foibles - my Megger very sensitive to battery voltage at the lower end. If its starting to give strange readings I can gurantee the low battery light wont be far off. I check mine against my checkbox every fortnight and record the readings for my scheme assessor - saves on calibration costs and you can spot things going weird long before the annual calibration.