Extending the ring vs spur

[JohnW2]

I do not agree with that - nor really know what you mean. .... Calculating loop resistance by adding Ze to (measured) R1+R2 IS the circuit impedance - true Zs. ... Deducting Ze from tester measured Zs is no indication of the actual circuit impedance. ...

I did say 'in some senses' - but I agree it would be 'incorrect' if the measured Zs was complicated by incidental oaths to earth.

Probably. I repeat. How would that work on your installation if the water pipe is replaced with plastic?

Well, silly though it may seem, the way it usually seems to 'work' in inspections of TT installations I've seen is that what is recorded on the form as "Maximum Permitted Zs" is usually (Uo / IΔn) (i.e. usually 7667Ω) together with (and this is the pretty silly bit) a recorded measured Zs for the circuit (~70Ω or whatever) - making it clear that (given reliance on the RCD for ADS) the Zs was 'well below' the 'permitted maximum'.

Measurement of Zs is seemingly silly/useless enough in this situation, and measurement of R1+R2 would (in relation to RCD-mediated ADS) probably be even more silly.

Kind Regards, John

 

[EFLImpudence]

I don't see what is silly about a maximum permitted Zs of 7667Ω and an actual of 70Ω, any more than a maximum permitted of 1.37Ω and an actual 1.3Ω.

The 7667 is just a nominal figure but that is the arithmetical maximum - like 23kΩ (or 46kΩ) for extraneous or not.



Ah - awaiting moderation.

 

[JohnW2]

I don't see what is silly about a maximum permitted Zs of 7667Ω and an actual of 70Ω, any more than a maximum permitted of 1.37Ω and an actual 1.3Ω.

The arguably 'silly' thing is bothering to (quantitatively) measure the Zs if one is going to 'accept' any figure below 7667Ω. However, I suppose one has to do it, just to confirm that there is some sort of earth connection (i.e. that the Zs is not approaching 'infinity') but, if there is any earth at all, the actual numerical value is neither here nor there.

Ah - awaiting moderation.

The software is obviously having "one of those days"

Edit: I see that this one is "awaiting moderation", too

Kind Regards, John