Earth Faulth Loop Impedance HELP!!!

[Deleted member 72666]

Cable operating temperatures and limiting temperatures under fault conditions are two entirely different scenarios...

Yes you're right....I'm easily confused these days!

 

[Engineer54]

The 80% rule of thumb is only intended to be applied to a test result taken from an impedance test. You have to ensure that the tested value does not exceed 80% of the tabulated value.

If the value is above 80% of the figure then improve the result this can be done by improving or providing additional earthing.

As i've stated elsewhere i rarely calculate impedance values they are always tested!! lol!!

As for improving the tested/calculated result, i think you'll find the modern formula for that scenario is bung a RCD in!! Or where one is already provided, who care's, the limit is 1667 ohms, so it's protected!! ...And there lies the far more important question than the 80% rule, when does additional protection become your main protection, by ignoring ADS requirements (other than on most TT systems that is) ??