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Zs taken by live test and r1 r2 calculated by deducting Ze or Zdb

Ro

Is the only reason you do not calculate r1 r2 by deducting Ze/Zdb from Zs is that it is down to parallel paths. The reason I am asking is, when the apprentices are doing their trade test, they are encouraged to short the circuit they are working on to the earth bar via a crocodile clip to get r1 r2. Surely this is picking up parallel paths also? Or is there is another reason?

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    The two tests measure different things, and on a new circuit to do a lower voltage DC test first before energising makes good sense. Equally once its all alive a Zs style loop test includes all external wiring  parallel paths etc and  is far closer to the actual fault situation that we hope will be blowing fuses and firing trips, which is the reason we need any CPC at all ;-) 

    The parallel path thing is a distraction - as you note both types of test can be fooled, depending what you leave connected or not,  but no live test should be done on any circuits where  the  main earth is not yet connected. 

    Mike.

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    The two tests measure different things, and on a new circuit to do a lower voltage DC test first before energising makes good sense. Equally once its all alive a Zs style loop test includes all external wiring  parallel paths etc and  is far closer to the actual fault situation that we hope will be blowing fuses and firing trips, which is the reason we need any CPC at all ;-) 

    The parallel path thing is a distraction - as you note both types of test can be fooled, depending what you leave connected or not,  but no live test should be done on any circuits where  the  main earth is not yet connected. 

    Mike.

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