Earth Fault Loop Impedence question

[kshah86]

hello, i got this qustion and would like someone to show me the working out of it please.

the measured value of loop impedance for a circuit is 0.83 ohms. if the temperature at the time of the test was 20c and the cable is 70c (factor1.2), what is the correct value. ze = 0.4 ohms

 

[telectrix]

your circuit resistance is multiplied bt 1.2 to allow for temperature. there fore, you would deduct the Ze from the Zs and adjust the remaining figure accordingly.

 

[Guitarist]

Surely the lecturers should go through all this with you before setting these questions as homework.

 

[Twistedfinger]

You cannot apply the correction factor to the measured value of loop impedance (Zs) as this includes the external loop impedance which is not subject to the 70c correction factor. So you need to subtract that from your Zs to give you your R1+R2 then apply the correction factor (1.2) then add the Ze back on.

The formula is:

= Ze + F(R1+R2)

Using your figures:

0.4 + 1.2 x 0.43 = 0.4 + 0.516 =0.916.

 

[iamelectric]

i dont understand this question surely the measured zs is the correct value

 

[telectrix]

i dont understand this question surely the measured zs is the correct value

it is. the question is badly worded. normally, we correct the max. value allowed to allow for temperature rise.