Zs readings slightly higher than ze+r1+r2

[ricardo123]

Hi,

This is my first post and hope someone can help.

I have tested a TN-S system and have these readings, I am constantly getting a higher Zs than the Ze+R1+R2.

The Zs is about 0.01 to 0.04 higher than my Ze+R1+R2 readings.

My Ze is 0.14 and PFC 2.1KA.

I have zero'd all 3 leads seeing a resistance of about 0.15ohms.

I am doing a standard Ze test (I hope) disconnect main bonding to exclude any parallel paths, remove main earth from CU, main switch is off, using 3 test leads, one on earth the other two probes on the incoming live and neutral into the CU main switch. I am using a fluke 1652 set to L-PE, Ik on the Loop test setting.

Any help would be appreciated.

 

[keniff]

measured and calculated rarely add up bang on, plus when you measure ze you have the earth disconnected, zs the earth is connected, generally when theres a difference in readings you give 0.05 tolerance so i wouldnt worry at all.

 

[rocker]

I wouldn't worry about it. The bits in your tester that test low ohm resistance are not the same ones that test loop impedance, it's quite common for the readings to be slightly different, I've found anyway.

 

[SirKit Breaker]

I wouldn't worry about it. The bits in your tester that test low ohm resistance are not the same ones that test loop impedance, it's quite common for the readings to be slightly different, I've found anyway.

Same here as well. And i have never had the same result twice when testing the same RCD's either.

Cheers.........Howard