uHeat Banner - Forum Discount Available
This official sponsor may provide discounts for members

Discuss Very high Zs reading in the Electrical Forum area at ElectriciansForums.net

M

mspms

Welcome to ElectriciansForums.net - The American Electrical Advice Forum
Head straight to the main forums to chat by click here:  American Electrical Advice Forum

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.
 
Electrical2Go - Online Electrical Supplier
This official sponsor may provide discounts for members
What's your Ze mate? When was your meter last calibrated? It could be a few things what earthing system is it?
 

telectrix

-
Mentor
Arms
Esteemed
try taking as reading on the L busbar. if that is high, then it's due to internal resistance of RCD and/or MCB. flick them on and off a couple of times. if that reading is OK, try at the terminals of the socket, not the front. try flicking the socket switch/es on/off.
 
R

Rauer

  • Thread Starter Thread Starter
  • #5
try taking as reading on the L busbar. if that is high, then it's due to internal resistance of RCD and/or MCB. flick them on and off a couple of times. if that reading is OK, try at the terminals of the socket, not the front. try flicking the socket switch/es on/off.
Never considered that but will remember it for future reference!!
 
M

mspms

  • Thread Starter Thread Starter
  • #6
TN-C-S. Ze seems very good at 0.09ohms
 
M

mspms

  • Thread Starter Thread Starter
  • #8
Thanks for your suggestion I will give it a go. Just to add more pain, I thought I would try a reading from a socket in my own home and again I'm getting +40ohms. Just coincedence?
 

Strima

-
Arms
Esteemed
What are you using to test the socket? Have you tried testing at the terminals on the back?
 
M

mspms

  • Thread Starter Thread Starter
  • #11
Sorry teletrix. It was a long day. I gave up and came home. The house is empty at the moment so no chance of any mishaps!
 
M

mspms

  • Thread Starter Thread Starter
  • #12
My Ze was really low at 0.09ohms. My meter has just been calibrated and it is a TN-C-S.

- - - Updated - - -

I'm using my 3pin plug and leads.
 
R

Rauer

  • Thread Starter Thread Starter
  • #15
Have you zero'd your leads on eloop?
 
M

mspms

  • Thread Starter Thread Starter
  • #16
Brand new RCD main switch today. I even tried with the old 2 pole main switch. still high.
 
Batteries going down? Bad contacts on the three pin plug? Dodgy terminations, any load on the circuit? (mainly an inductive might cause a false reading) What make of RCD is it?
 
M

mspms

  • Thread Starter Thread Starter
  • #20
Just a quick note I have just tried a socket in my place and I;m getting 48.1ohms with a pefc of ony 4.78amps.
 

Richard Burns

-
Mentor
Arms
Esteemed
Do check your settings on the meter and the battery level just in case.
Then try testing in your house as close to the origin as possible, without any switches, just the supply and see what reading you get, if it is still +40ohms then sounds like a leads or meter problem.
What reading do you get on testing resistance on the leads?
 
R

Rauer

  • Thread Starter Thread Starter
  • #24
Try it with your probe leads and not your plug top lead
 
M

mspms

  • Thread Starter Thread Starter
  • #26
I have spent the last 2 days going through the entire house checking and testing and putting right some very sorry wiring expecially on the R2 side of things. I am happy with all of the wiring and the results that I have had on the continuity and resistance side of things. it is this very high Zs I can't seem to fathom out. The RCD is a Hager.
 
Switch off your meter, remove all batteries, wait then put them back and try again. I am running out of ideas.
 
R

Rauer

  • Thread Starter Thread Starter
  • #29
Plug top lead sound a bit suspect to
Me at the mo
 
R

Rauer

  • Thread Starter Thread Starter
  • #31
Have your zero'd your plug top lead on e loop?
 
M

mspms

  • Thread Starter Thread Starter
  • #32
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

-
Mentor
Arms
Esteemed
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.
 
M

mspms

  • Thread Starter Thread Starter
  • #34
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.
 

Richard Burns

-
Mentor
Arms
Esteemed
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.
 
M

mspms

  • Thread Starter Thread Starter
  • #37
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.
 
S

StuSpiers

  • Thread Starter Thread Starter
  • #38
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

-
Mentor
Arms
Esteemed
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.
 
R

Rauer

  • Thread Starter Thread Starter
  • #40
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

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

Deleted member 26818

  • Thread Starter Thread Starter
  • #42
Try doing the adiabatic with that figure.
 
E

Edd

  • Thread Starter Thread Starter
  • #44
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
 
Last edited by a moderator:
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!!!
 
S

SKY

  • Thread Starter Thread Starter
  • #46
24KA - jesus - I never really see more than 2KA around my next of the woods.
Seen 5.9KA in London which if I recall is the highest I have seen.
Are you local to Essex? if so you can borrow my spare calibrated meter if you like.
 
Wetroom Store - Network Wetroom Suppliers
This official sponsor may provide discounts for members

Reply to Very high Zs reading in the Electrical Forum area at ElectriciansForums.net

Top Bottom