earth loop

[matt12321]

the maximum tabulated value of earth fault loop impedance for a circuit 1.85 ohms. if the resistance of the line and cpc of a new circuit is 1.03 ohms. whats the maximum accepted external earth loop impedance value

 

[Spudnik]

Please post all training related question in this forum and not the General forum.

Thanks.

 

[topquark]

As your Zs = (R1+R2) + Ze you can work it out, transpose by subtracting (R1+R2) from both sides of the equation:

Ze (Max) would be Zs - (R1+R2)

Which would give you 0.82 Ohms max

 

[matt12321]

it more of a question than training really .

 

[matt12321]

cheers topquark

 

[matt12321]

im such a dumb ---. i feel the way it was worded confused me then lol

 

[topquark]

Be a little cautious when you see the word tabulated though, if you're dealing with current cable limits you'll find that the values in the on site guide are 80% of those in the BRB. See what the question is asking for as to whether you need to adjust the values you're given or not.

 

[topquark]

Just think about how the resistance of the fault path is made up. Ze = external, external to the circuit under test. The R1+R2 value is the total resistance of all the line conductor in series with the CPC (ie the maximum resistance if the fault was right at the end of that circuit (it'll typically be less than that but you use the worse case scenario for safety)). HTH.