help with Zs.

[tgtworsley]

please can someone help me. doing a test on a new build and my results are not matching up. all my Zs are way to high. for example on the cooker circuit measured R1+R2 = 0.04, The measured Ze at the board is 0.08 (PME) so Zs should be around 1.2 but my measured is 0.79 is that right if not any idea's

 

[Paul.M]

Check the connection of the main earth cable on the MET.

Ps welcome to the forum. And we all know its a typo error and you ment 0.12 and not 1.2 lol.

 

[GaryM]

Parallel earths (bonding conductors) may result in a lower measured Zs than a calculated Zs (Ze+(R1+R2)).
Note either, doesn't matter. You can always make a comment on your EIC regarding the spurious looking results if you choose to record the measured Zs results.

 

[tgtworsley]

thanks for replay all seems ok on the MET. i disconeted and bonds when i got this reading and it went to 0.75 i'm using this job for my niceic inspection on wednesday

 

[Paul.M]

Good point Gary M but he's getting higher readings not lower readings due to parallel paths.

If all readings are about the same difference on each circuit and not just the cooker, I would be checking terminations on the MET, first place I'd look anyway.

 

[Paul.M]

posted at the same time, forget what I said, sorry Gary .

With bonding 0.08

Without bonding 0.75

You've answered your own question.

 

[telectrix]

or inaccurate Zs readings when measured using no trip.

 

[tgtworsley]

sorry but the Zs reading goes down to 0.75 when i disconnect the bonding which is still way to high

 

[GaryM]

thanks for replay all seems ok on the MET. i disconeted and bonds when i got this reading and it went to 0.75 i'm using this job for my niceic inspection on wednesday

So the measured Zs was lower with protective bonding disconnected? 0.75ohms against 0.79ohms?

As a side point - don't disconnect protective bonding on a live installation, especially in front of your NICEIC inspector!

Edit, just seen the typo - should be 0.12ohms and not 1.2ohms for calculated Zs. Id put this down to inaccurate measurement due to the no-trip setting of your meter.

 

[telectrix]

the cooker circuit measured R1+R2 = 0.04


​that reading don't lookm right to me. far too low. unless the cable is only about 4m in length.

 

[tgtworsley]

sorry got them 2 mixed up, Zs was 0.75 with bonding connected and was 0.79 disconected. i know that, was just trying to find out why so high thanks lol.
lenght of cable is about 5 meters from the board

 

[spark 68]

Did you 'Zero' your meter before measuring your R1+R2 ?

 

[tgtworsley]

yer i zero the leads before each use

 

[Engineer54]

please can someone help me. doing a test on a new build and my results are not matching up. all my Zs are way to high. for example on the cooker circuit measured R1+R2 = 0.04, The measured Ze at the board is 0.08 (PME) so Zs should be around 1.2 but my measured is 0.79 is that right if not any idea's

Your Ze measured value sounds too good to be true!!!

 

[tgtworsley]

thats what i thought at first, measured it a few times.