r1 + r2 by taking away ze from zs

[dannyv]

Is it alright to take away ze from zs to get r1 + r2 reading

 

[telectrix]

NO<NO<NO. how can you measure Zs when you have to measure R1+R2 before energising the circuit.( note the use of capitals for R )

 

[Sparky Ninja]

No you cannot.

You need to measure R1&R2 to verify both polarity and the presence of conductors before energising the supply.
Also, a measured Zs test will incorporate parallel paths which will more than likely indicate an inaccurate R1&R2 if obtained by calculation.

 

[Guest123]

Is it alright to take away ze from zs to get r1 + r2 reading

No indeed.

A measured Zs value will include any additional parallel earth paths that may be present in the installation......protective bonding for instance, so the Zs-Ze will not be a true reflection of the resistance of the line & CPC conductors of the circuit in question.

 

[dannyv]

some electrician i know told me he does it when carrying out PIR's

 

[Sparky Ninja]

some electrician i know told me he does it when carrying out PIR's

He's doing it wrong and in non-compliance with BS7671.

I know a couple of nationwide companies who also do this..

 

[Guest123]

some electrician i know told me he does it when carrying out PIR's

Doing it wrong then isn't 'he'.......

 

[Sintra]

And after he has finished he has to feed his horse.

 

[Sparky Ninja]

Probably a very tired horse as well. Galloping to 7 or 8 periodics a day at £50-80 a go taking 30 minutes a piece.

 

[telectrix]

but is it necessary on a PIR to measure R1+R2, as the circuit has already been verified when installed and energised. measurement of Zs, when compared to previous readings should confirm that the R1+R2 is satisfactory.

 

[Sparky Ninja]

but is it necessary on a PIR to measure R1+R2, as the circuit has already been verified when installed and energised. measurement of Zs, when compared to previous readings should confirm that the R1+R2 is satisfactory.

Well if you didn't then how would be able to test polarity (things like switching of the Line conductor only), or things like open circuits on ring finals and bridges within them?

 

[Sintra]

Probably a very tired horse as well. Galloping to 7 or 8 periodics a day at £50-80 a go taking 30 minutes a piece.

Yep one of the reasons this trade is in the state that it is in.

 

[morph]

Well if you didn't then how would be able to test polarity (things like switching of the Line conductor only), or things like open circuits on ring finals and bridges within them?

live polarity with ZS
open circuits ? do you mean one conductor disconected making a big radial?
well by comparing the ZS from previous PIR

 

[Sparky Ninja]

live polarity with ZS
open circuits ? do you mean one conductor disconected making a big radial?
well by comparing the ZS from previous PIR

Don't you start on me in this one.

 

[morph]

Don't you start on me in this one.

ha ha , was just an offering