help with Zs.

[nickblake]

There were other similar posts with similar issues and they appeared to come to the same conclusion.
Your were happy with your other results, quality of workmanship and you are using a calibrated tester. You will see the problem when you go back and retest as the others suggested

thats a great Ze 0.08 is the substation in the lounge just for curiosity whats the PFC , does seam a tad low

 

[tgtworsley]

lol the PFC is 3.0 ka

 

[Engineer54]

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

Quite frankly, the only way your going to accurately measure true values this low, is with an EL test kit that has high resolution, these are generally used in sub-stations etc. Or you could use IQ's method that can be found in the ''Stickies'' which is a much cheaper alternative!! (link at bottom of this post) I wouldn't be relying ''directly'' on an MFT loop testing range, be it on the no-trip or full current setting...

You must have a local DNO distribution TX in next doors garden, or very close by anyway... lol!!


LINK....
http://www.electriciansforums.net/inspection-testing-certification-electrical-installations/31838-higher-accuracy-low-ze-test-procedure.html

 

[Farmelectrics]

would his inspesctor let him calculate his zs or would he exspect a measured value

 

[SPARTYKUS]

You can get quite high PSCC's with these sorts of scenarios. Sometimes well over 6kA

 

[Engineer54]

lol the PFC is 3.0 ka

3 KA, on a Ze of 0.08 ohm's, am i missing something here or what??? When was the last time your test equipment was calibrated by the way??

 

[tgtworsley]

was calibrated in april and i do test it all the time.

Found the problem it's the rcd's. next question is would you change them or make a note of it on the test form. would it be ok for the niceic inspector

 

[wallyanker]

U/Ze = 230/0.08 = 2875

Rounded up, 3 Ka sounds about right to me. Or have I done it wrong....lol

 

[spark 68]

Found the problem it's the rcd's. next question is would you change them or make a note of it on the test form. would it be ok for the niceic inspector

For the purposes of your EIC you can put your measured Ze and your measured (R1 + R2), and a calculated Zs, Zs = Ze + (R1 + R2), as this is an acceptable method, and will be fine for your assessment.

What is not acceptable is to back calculate from a measured Zs.

 

[tgtworsley]

do i need to change the rcd's or will it be ok

 

[SPARTYKUS]

For the purposes of your EIC you can put your measured Ze and your measured (R1 + R2), and a calculated Zs, Zs = Ze + (R1 + R2), as this is an acceptable method, and will be fine for your assessment.

What is not acceptable is to back calculate from a measured Zs.

....like the new meggar meter gives a value for!!!

 

[spark 68]

do i need to change the rcd's or will it be ok

Changing the RCD's will likely not change your results unless you are changing the manufacturer or type, there have been a few threads on here regarding certain makes of RCD skewing the Zs results.

You cannot realistically replace the RCD's with another make unless you are willing to change the CU.

Your measured Zs will always be slightly different due to either parallel paths or to the 'no trip' setting of your MFT, some MFT's are better than others in this respect.

You can, as I (and others), have already said just put down your calculated Zs results, so long as you have a measured Ze and (R1+R2).

You should not really put a calculated Zs down from anything other than a measured Ze, ie. by enquiry etc.

 

[spark 68]

....like the new meggar meter gives a value for!!!

Hi Sparty,

I cannot really comment on the 'new' Meggers, but from what I have read on here they seem to have had less than stellar reviews, requiring software updates etc.

 

[tgtworsley]

ok thanks for the help

 

[GaryM]

U/Ze = 230/0.08 = 2875

Rounded up, 3 Ka sounds about right to me. Or have I done it wrong....lol

Nope, and 3000 / 0.08 = 240V so the figure is well and truly in the ballpark.