Calculating R1+R2 is it allowed?

[electrospark]

R1+R2 = Zs -Ze
Just wondering peoples thoughts on this. Some people tell me its okand others say you shouldn't calculate it for the purpose of a pir.

 

[rebuke]

When you measure Ze you should have any parallel paths (such as bonding etc) removed, as such while calculating Zs by taking Ze + R1+R2 is fine as it gives you a conservative value for Zs (likely a measured value would be lower), doing the inverse and calculating R1+R2 by using a measured value for Zs will almost certainly result in you getting a lower value for R1+R2 than the true one as the parallel paths will reduce your Zs measurement...

 

[JohnW2]

When you measure Ze you should have any parallel paths (such as bonding etc) removed, as such while calculating Zs by taking Ze + R1+R2 is fine as it gives you a conservative value for Zs (likely a measured value would be lower), doing the inverse and calculating R1+R2 by using a measured value for Zs will almost certainly result in you getting a lower value for R1+R2 than the true one as the parallel paths will reduce your Zs measurement...

..or, with TT, a large negative calculated R1+R2 (provided that Ze is measured with all parallel paths removed)!

Kind Regards, John.

 

[Risteard]

Although it should be said that there may be no need to record R1+R2 values on a periodic inspection. Continuity of cpcs can be verified by means of an Earth Fault Loop Impedance test on an installation which has already been energised.

 

[Lectrician]

On a periodic you may calculate. No reason why not, and it's a waste of time doing both.

On an EIC you MUST measure the R1+R2 as a dead test before energising. You can then calculate the Zs if you wish - No point doing both.

For a ring, the r1+r2 / 4 is your R1+R2.

 

[RMS]

R1+R2 = Zs -Ze
Just wondering peoples thoughts on this. Some people tell me its okand others say you shouldn't calculate it for the purpose of a pir.

No problems as long as its stated in the limitations box of the report and agreed with the client if necessary.

If i'm not carrying out this test then rather than calculate it I insert LIM in the box.

 

[Risteard]

As I said there's nothing wrong with agreeing with the Client that the test is unnecessary. However, it is not correct to subtract Ze from Zs and so it should never be calculated. As someone has said, if it is an agreed limitation then LIM is correct.

 

[electrospark]

Thanks guys. I thought it was ok to calculate it and had done for years then my boss said that our nic inspector didn't like it. Obviously in a new install then this would be measured before energized. Thanks again