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Topic Title: Recording clearly 'wrong' test results?
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Created On: 15 February 2013 08:53 PM
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 18 February 2013 11:35 AM
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Richard64

Posts: 231
Joined: 15 October 2009

Originally posted by: Jaymack

Originally posted by: daveparry1

That doesn't take into account parallel paths though Gary, (probably doesn't matter that much in practice though)


Au contraire, In general, a Zs measurement errs positively and proof of the pudding, if a supply is available! For belt and braces one could carry out both



A person with 2 watches never knows the correct time!



Regards


Exactly:
You need the most onerous reading that doesn't take account of parallel paths, because they may not always be there.
That's why, Ze bonds off, PFC bonds on.
I always add Ze to R1+R2 to get Zs
 18 February 2013 05:36 PM
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daveparry1

Posts: 6200
Joined: 04 July 2007

Yes i'm fully aware of how to conduct a Ze test but I do like to see a Zs reading too, that's the only sure way of knowing the earth is connected! Just suppose you done your R1+R2 test but forgot to re-connect the earthing conductor or that it broke off at the point of connection to the earth bar when you done the screw up! Unlikely admittedly but not unknown,

Dave.
 18 February 2013 05:55 PM
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Richard64

Posts: 231
Joined: 15 October 2009

Dave,
I agree that a final Zs is a good way to check all is connected OK.
But which reading would you use for the cert?
The Ze Plus R1 + R2 or the final Zs?
 18 February 2013 06:06 PM
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daveparry1

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I use the dead test R1+R2 and the measured Zs, or if I can't for some reason do a proper R1+R2 test I do an R2 test with the long lead, (eg often lighting circuits on c/unit changes)

Dave.
 18 February 2013 10:42 PM
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sparkingchip

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If you measure Ra the earth electrode "resistance" with a loop tester then it would actually be a impedance wouldn't it? then to this impedance you add R1 & R2 which is a true resistance, then you have the RCD which has brought a bit more impedance to the circuit, but you are choosing to disregard this additional impedance.

Why? Zs is the total impedance isn't?

Electrical impedance

Andy

Perhaps you are using this reference book, "Warning! The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased."
 19 February 2013 06:01 AM
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Thripster

Posts: 639
Joined: 22 August 2006

Contact attitude of probes seems to be greatest reason for unexpected results. You can take five sets of readings at the same terminals within sixty seconds and all readings be different. Perhaps oxidisation at the contact surfaces? Or perhaps there is a dynamic reason , external to the installation, which could explain the difference in results?

Regards
 19 February 2013 08:47 PM
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sparkingchip

Posts: 6031
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" The impedance of the circuit is given by Z = V/I, where Z is a complex number given by Z = R + jX. R, the real part of the impedance, is the resistance of the circuit, and X, the imaginary part of the impedance, is the reactance of the circuit."

I still think there is a general inclination to disregard the RCD, the little device with its coils and magnetic fields which is the X, the imaginary part of the impedance.

Andy
IET » Wiring and the regulations » Recording clearly 'wrong' test results?

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