Loop Impedance tester electrical circuit

[marcuswareham]

Hi

A quick one I was wondering if anyone knows how a multifunction tester performs a loop impedance test.

I understand how to perform a test and what the results of a loop impedance test give you in working out your PSCC and earth fault current. I use my Fluke multifunction tester every day at work to do just that.

I have however seen 13a plug in style socket testers which also so an earth loop impedance test (even if the results are very vague and not particularly useful). I am just wondering how these socket tester work as they are still relatively cheap so there must be some basic circuit doing the loop test

Hope that makes sense

Thanks Marcus

 

[Risteard]

Many loop testers inject a current and measure the Volt drop on the supply to determine the impedance.

 

[Lucien Nunes]

The plug-in testers like the Socket-and-See that do loop impedance tests actually incorporate a microcontroller that operates a current injection circuit and takes a measurement. It's just a compact, not very precise version of what is in an MFT. It would be interesting to find some patent numbers if there are any and look up the details. These days it is possible to buy and program a fully functional digital computer for less than the price of the dropper capacitor that powers it from the mains.

 

[R-fur]

On a historical note I believe the original testers measured the neutral earth loop as that was easier and safer. However when the supply boards started multiple earthing of the neutral in the 60's that was no longer an option and the live earth loop tester was developed.