Garden Office supply

[DetlefSchmitz]

er Mikebar - what do you think the resistance to ground of a typical earth rod is?

 

[plugwash]

er Ban all Sheds- Zs will vary with the length of cable run, that's what I'm concerned with here. One way to lower a Zs value to meet a disconnection time, as I'm sure you know, is to make a better earth provision. I'm thinking of doing that by putting and earth rod in, if need be.

The impedance of two fault current paths will be at best the paralell combination of those paths and worse if the two paths have shared elements.

Adding a high impedance path (your rod and the suppliers rod) in paralell with a low impedance (a non faulty TN earth) will have a negligable impact on the overall impedance.

 

[ban-all-sheds]

er Ban all Sheds- Zs will vary with the length of cable run, that's what I'm concerned with here. One way to lower a Zs value to meet a disconnection time, as I'm sure you know, is to make a better earth provision. I'm thinking of doing that by putting and earth rod in, if need be.
The imaginary Ze problems you refer to, if they ever arise, demand a different solution as I'm sure you also know.

What I know is that Ze is one of the components of Zs, and that ignoring any parallel paths the other component is the R1+R2 of the final circuit.

What I know is that if you measure Zs, and it's too high, the problem is not the 150 - 200mΩ of the cable, it's your Ze, and it's not imaginary.

What I know is that the maximum measured EFLI for a B16 is 2.32Ω, and if it's more than that at the end of 40-odd m of 10mm² SWA and few m of 2.5mm² T/E your Ze is going to be over 2Ω.

Your point about extraneous conductive parts isn't valid, for obvious reasons.

So you've exported your TN- earth.

If you had a hollow metal cylinder coming out of the ground into the shed it would be an extraneous-conductive-part.

So please tell me the obvious reason why a solid metal cylinder coming out of the ground into the shed is not an e-c-p, because it's not obvious to me.