EFLI in 2391 land.

[malcolmsanford]

If your doing this as an answer in the 2391-10 then just draw a simple single phase diagram, don't throw the added pressure of trying to include a 3 phase system, after all you don't draw the star connection of the transformer, you just use to put two horizontal lines parallel to each other and label it transformer.

Though it nearly 15 yrs ago when I did my 2391, but all the guys that have taken recent ones that I checked over for them all just did the above type drawing.

 

[brucelee]

yes Malclolm is correct keep it as simple as pssible just draw a earth fault loop diagram of a single phase install
Just make sure you label correctly with all correct terminology and show fault path in red with little key for the simple ie a red line with a arrow indicating direction of fault path simple

 

[WayneL]

........ZE which on a TT is RA

ZE or Ra is the external earth fault loop impedence Ie suppliers side

A bit of confusion here, I think, 'Bruce'

Ze, as the 'Z' implies, is external earth fault loop impedance, regardless of the earthing system.

Ra, as the 'R' implies, is the resistance of the earthing conductor and the earth electrode, to earth.

Two totally different entities.

Ra is resistance and is measured with an 'earth electrode resistance tester' - this is a dead test.

Ze/Zs is impedance and is measured with an 'earth loop impedance tester' - this is a live test.


This also means that the OPs second question is worded very badly when asking for the method of measuring electrode 'resistance', then giving the answer for measuring the Ze (impedance).