Spot the mistakes - Billy Bulls**t circuit sheets i think

[IQ Electrical]

by calculation, you are correct, but due to parallel paths (water pipes etc.) to earth, the Zs can be lower than calculated. this is most noticeable in TT systems where the resistance to earth through services is less than the resistance through the earth rod.

This is why the Zs-Ze = (R1+R2) formula should never be used as it makes no allowance for the parallel paths that exist in all but the most basic of 'all-insulated' installations.

 

[telectrix]

take a few readings and compare with them. that should give an idea.

 

[rallyandy]

i,m back ther tomorrow so will start taking my own readings, i was going off the existing readings today for an overview of the existing installation

 

[rallyandy]

i think i need to review my test procedures , i have always measured Ze at the supply incomer, then R1 + R2 and added them together obviously not allowing for parallel earths, you learn something new every day on here and i dont mind admitting it

 

[telectrix]

i always measure Zs unless by doing so i might create danger for myself or others. to give an idea of the effect of parallel paths, measure Ze as normal with the main earth dissed. then measure again with it connected. you should find the 2nd reading is lower.

 

[IQ Electrical]

i think i need to review my test procedures , i have always measured Ze at the supply incomer, then R1 + R2 and added them together obviously not allowing for parallel earths, you learn something new every day on here and i dont mind admitting it

Your procedure still complies, measurement or calculation.

I'm a confirmed measurer!

 

[eskimo39]

Me too!

 

[rallyandy]

i always measure Zs unless by doing so i might create danger for myself or others. to give an idea of the effect of parallel paths, measure Ze as normal with the main earth dissed. then measure again with it connected. you should find the 2nd reading is lower.

I will try that tomorrow as the hotel is vacant week days and see what results i get , many thanks Telectrix

 

[rallyandy]

Hi guys ... just to keep you updated ... i havent been back to the job yet but should be back there monday so will let you know what i find
Andy

 

[spark 68]

to give an idea of the effect of parallel paths, measure Ze as normal with the main earth dissed. then measure again with it connected. you should find the 2nd reading is lower.

Shouldn't this be done anyway, as your as part of your PFC test (PEFC) ?