Earth loop impedence Zs for 3ph systems

[Test Probes]

I know on a 3 phase supply system ie; a DB, you measure PFC & PFCC taking the highest of the two reading and doubling it. This is then recorded. But what about say a 3 phase motor for example where you measure each Line and record it on the schedule of test results. Is the result recorded as is or do we have to double it?

 

[i=p/u]

only record the highest , and yes pscc and pefc make up pfc lol

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and yes double it

 

[Test Probes]

Many thanks. That is what I did but my supervisor questioned me about such a high reading even when I pointed out that it was a 3 phase item.

 

[i=p/u]

well you on double pfc not zs reading

 

[tony mc]

Explain again what reading was high the R1 + R 2 on the motor CCT or the PFC (PSCC) ?

 

[Test Probes]

I was measuring two 3 phase air conditioner on the roof of a building which we were testing. Dead test had been completed. We then tested live for earth loop impedence Zs. I tested L1, L2 & L3. I then doubled each of the results and recorded each result on the schedule of test result form. There were a number of 3 phase items on the on DB as well.

The PFC was normal but I doubled it and my supervisor said it was too high. I don't think he realised I had doubled the result.

 

[tony mc]

Thats why your results are being questioned.

Test ZS at the air con unit and record the highest of the 3 you do not double the reading !

 

[i=p/u]

yeah you dont double the zs readings just the pfc at origin and on a tn-c-s only need to test once as will be the same...

 

[Test Probes]

OK, thanks. I'll correct my recordings on the schedule of test results.

 

[plugsandsparks]

If your meter measures PSCC across phases then you dont double.