Why do i need a rewire when i've passed inspection with no issues?

[timhoward]

Hmmm maybe a spur on a spur in the ring, or is the house that big that you would have a circuit length of 50+ metres on 2.5/1.5 T&E?

You forgot to take off the Ze (0.36 in this case). So we're talking about 0.67 ohms worth of actual circuit, so more like 28m of cable which is plausible for a ring final circuit that covers more than one floor.

 

[Acca dacca]

You forgot to take off the Ze (0.36 in this case). So we're talking about 0.67 ohms worth of actual circuit, so more like 28m of cable which is plausible for a ring final circuit that covers more than one floor.

Ah yes my bad! Although interesting on the schedule of results the figure 0.36 is recorded as the Zs? and Not Ze....And the Ipf is quoted as 1.06kA?

 

[timhoward]

Ah yes my bad! Although interesting on the schedule of results the figure 0.36 is recorded as the Zs? and Not Ze....And the Ipf is quoted as 1.06kA?

On the 1st page it gives 0.36 as the Ze (twice in fact!). I can't spot where you mean for 0.36 Zs.

The confusion over the 1.06Ka is because the property has TNS earthing. As your profile says you are a trainee I'll elaborate a bit....(hang in there!)

The Ipf is the highest of prospective dead shorts of Live-Earth and Live-Neutral and as this property has TNS earthing the two will differ due to the different sizes of the two cables all the way back to the substation transformer. (If it were TNCS earthing then due to the neutral-earth link in the cut-out the values would be the same)

The path back to the transformer through the neutral has a lower impedance of 0.21 ohms (working backwards from 1060 amps) as it's a bigger wire. This makes sense.
So the maximum fault current Line-Earth is 638 amps (230/0.36) and the maximum fault current Line-Neutral is 1060A.
The installer recorded the higher of the two (correctly).

 

[Acca dacca]

On the 1st page it gives 0.36 as the Ze (twice in fact!). I can't spot where you mean for 0.36 Zs.

The confusion over the 1.06Ka is because the property has TNS earthing. As your profile says you are a trainee I'll elaborate a bit....(hang in there!)

The Ipf is the highest of prospective dead shorts of Live-Earth and Live-Neutral and as this property has TNS earthing the two will differ due to the different sizes of the two cables all the way back to the substation transformer. (If it were TNCS earthing then due to the neutral-earth link in the cut-out the values would be the same)

The path back to the transformer through the neutral has a lower impedance of 0.21 ohms (working backwards from 1060 amps) as it's a bigger wire. This makes sense.
So the maximum fault current Line-Earth is 638 amps (230/0.36) and the maximum fault current Line-Neutral is 1060A.
The installer recorded the higher of the two (correctly).

Im referring to the additional images further along the thread, if you look at image marked cert4 that's where the Zs figure of 0.36 in the 2nd box is. Thanks for pointing the TNS earthing arrangement out, in my haste I neglected to notice that, perhaps ive miscalculated something along here but i made the mistake/error of calculating (230/1.04) 1.04 being calculated on the circuit #4 for the R1+R2+Ze, if that clarifies/muddy's the water..