Sorry but Ra = Ze ?

[Cider]

Hi all

New to this but am i correct in thinking (having looked at gn3, on site guide and another testing book) that the measurement taken for earth rod resistance is also the ze as both tests seem to be taken in the same way (megger connected between disconected rod and phase live side of main isolator turned off).

Also the earth fault reading taken in ohms is multiplied by the voltage to give earth fault current divided by 1000 to give kpa.
Short circuit test between R1 and N give direct kpa.
Both taken with rod connected but main switch off.

Hope this makes sence.

Be kind if im wrong!

Cider

 

[Sparky Ninja]

Hi all

Also the earth fault reading taken in ohms is multiplied by the voltage to give earth fault current divided by 1000 to give kpa.


Cider

That's not ohms law though is it.

 

[Deleted member 26818]

What is this earth fault reading that is taken in Ω?
Do you mean the earth fault path resistance taken in Ω?
Do you then mean that the measured voltage is divided by the earth fault path resistance and then divided by 1000 to obtain the Prospective Earth Fault Current in kpa, or perhaps the more commonly used units of kA?

 

[Cider]

sorry, KA not kpa.
I got 96.1 ohms before i repaced the rod which had an Ra of well over 200.
Ive not had a chance to do fault currents again but want to get an understanding of the earh fault reading.

Thanks again.

 

[Deleted member 26818]

Ze/Ra is the term given to the resistanc of the earth fault path.
Your reading of 96.1Ω is OK, but not fantastic. Obviously it's better than over 200Ω.
Your PEFC will be quite low, using a nominol voltage of 230V, it will be 2.39A, if you wanted to divide by 1000 it will give a kA of 0.00239kA.
This is to be expected with TT installations, and is why an upfront RCD is required to provide ADS.
Your PSSC will be a lot higher, more in common with TN-S and TN-C-S installations.

 

[PC Electrics]

sorry, KA not kpa.
I got 96.1 ohms before i repaced the rod which had an Ra of well over 200.
Ive not had a chance to do fault currents again but want to get an understanding of the earh fault reading.

Thanks again.

Cider.
it's important to get the units correct from the earliest stage of your learning. To that end:
it's kA (for kilo amps), not KA [note the small k in the correct term].

FYI: kPa is kilo pascals and are units of pressure

Have a look here to brush up on your units:
International System of Units - Wikipedia, the free encyclopedia
SI derived unit - Wikipedia, the free encyclopedia

 

[Cider]

Cider.
it's important to get the units correct from the earliest stage of your learning. To that end:
it's kA (for kilo amps), not KA [note the small k in the correct term].

FYI: kPa is kilo pascals and are units of pressure

Have a look here to brush up on your units:
International System of Units - Wikipedia, the free encyclopedia
SI derived unit - Wikipedia, the free encyclopedia

Point taken ; )

Ive got an F gas course coming up hence the kPa

 

[mattmoo1974]

KP make peanuts NUFF Said!!!