Very high Zs reading

[mspms]

Good evening all. I wonder if anyone could give me a steer as to why I am getting very high Zs readings. I have been testin a circuit that has a R1+R2 of 0.23 ohms but I seem to be getting Zs reading on L-E of + 40ohms. L-N is coming in at 0.2ohms. The incoming fuse is a 63amp BS1361 an RCD main switch protecting all circuits. All other tests are fine. I am wondering whether it could be my meter not reading correctly on the Zs test. Any ideas?

Thanks all.

 

[Rauer]

Have your zero'd your plug top lead on e loop?

 

[mspms]

I have just tested at the terminals of the same socket with my 3 test leads and am now getting 0.01 ohms and 23.00 Ka.

 

[Richard Burns]

Change your plug tester unit!
But try a few contiuity tests through the unit first and see that there is not dirt in the connections or bent pins from dragging around in your tool bag.

Edit
No hang on 0.01ohms sounds a bit low for a standard value, could be, but 23kA is too high for a domestic CU.

 

[mspms]

Gentlemen, thankyou for your time and patience. I will try again with just my probes and see what I get. Just one other question; why does a main switch RCD trip whwn carrying out Zs testing? i had one the other day, another empty house and need to go back to sort it.
Kind regards.

 

[Strima]

Post #10... :lol:

Have you got a 'no trip' setting on your MFT?

 

[Richard Burns]

When testing Zs a current of about 20A is used to test the resistance, this will trip an RCD (and possibly a 6A MCB), no trip or trip lock limits the current to 15mA or so but may give a different reading.

 

[mspms]

I don't think some of my posts are being sent. I have tried my three probes at my socket terminals and am getting 0.01ohms with a PEFC of 24Ka. So I think the problem is solved.
Just one more thing; I had a RCD main swith ch trip on me whilst carrying out Zs test the other day. I need to go back and sort it ( It's an empty house) What could be causing the RCD main switch to trip? I was using my plug adapter again>
Many thanks.

 

[StuSpiers]

I would still be worrying with those results.

0.01ohms for ZS??

24Ka ???

Wouldn't like to be in that house when that kind of fault current flows.

Your meter sounds f***ed - did they cock up the calibration?

 

[telectrix]

something is definitely wrong here. to get a Zs of 0.01, you would have to have a -ve value for R1+R2 .l try and borrow another MFT.

 

[Rauer]

something is definitely wrong here. to get a Zs of 0.01, you would have to have a -ve value for R1+R2 .l try and borrow another MFT.

Or a lot of good parallel earths!!!

 

[telectrix]

wouldn't like to see the state of a 1.5mm cpc after 24KA been up it , even for a fraction of a second.

 

[Deleted member 26818]

Try doing the adiabatic with that figure.

 

[telectrix]

Try doing the adiabatic with that figure.

66mm2??

 

[Edd]

I had a Fluke 1652 giving me readings like that once, sent it off to be calibrated all came back ok, but it still gave random readings, its now in the stores! Test at a socket then at the mcb for that circuit (not at main switch as the RCD needs to be taken into account). then at the main switch. Tell us what readings you get

 

[Guitarist]

I don't think some of my posts are being sent. I have tried my three probes at my socket terminals and am getting 0.01ohms with a PEFC of 24Ka. So I think the problem is solved.
Just one more thing; I had a RCD main swith ch trip on me whilst carrying out Zs test the other day. I need to go back and sort it ( It's an empty house) What could be causing the RCD main switch to trip? I was using my plug adapter again>
Many thanks.

I would say that the problem here is far from solved. Firstly, I don't believe that figure for a second, so something wrong with either testing or meter. Secondly, do you know what a standard switch/MCB is rated at? Certainly not 24KA!!!