Told I need to have Ze checked, an R1+R2 test, and possibly downrate a 40A fuse to 32A - any way to save money here?

[Risteard]

Whenever I have reported a Ze above 0.8 for TN-S and 0.35 for TN-C-S, the DNOs have attended to get it below those readings.

That doesn't imply any statutory obligation, however. These are usual maximum values, but should not be misconstrued as maximum allowable values.

 

[JohnW2]

That doesn't imply any statutory obligation, however. These are usual maximum values, but should not be misconstrued as maximum allowable values.

All agreed. However,as I've been writing and implying, when one talks about 'high TN Ze', I don't think it unreasonable to regard that as meaning "higher than 'the usual maximum values' '",do you?

 

[Risteard]

All agreed. However,as I've been writing and implying, when one talks about 'high TN Ze', I don't think it unreasonable to regard that as meaning "higher than 'the usual maximum values' '",do you?

Sure, but that wasn't my point. This belief that the DNO are duty-bound to address higher than usual values because of misunderstood guidance in BS7671 guidance documents is misplaced.

 

[JohnW2]

Sure, but that wasn't my point.

I realise that, but it is relevant in relation to the point about which I was 'taken to task'.

This belief that the DNO are duty-bound to address higher than usual values because of misunderstood guidance in BS7671 guidance documents is misplaced.

I really don't know where this (seemingly very widely-held) belief comes from, nor whether it is true or not, but I don't think it has got anything to do with BS7671 or associated documents.

I must say that,given the crucial importance of a satisfactory earth to the safety of electrical installations, I would have expected that, if a DNO supply an earth, there would (should) be a legal obligation for them to 'maintain' it such that it remained adequate to provide the expected/required levels of safety.

 

[securespark]

I started in the industry in 1983 and in all that time the DNOs have always rectified Ze readings over 0.35 or 0.8 that I have reported to them.

And there have been many over those years.

 

[JohnW2]

I started in the industry in 1983 and in all that time the DNOs have always rectified Ze readings over 0.35 or 0.8 that I have reported to them. And there have been many over those years.

That again corresponds to what I have always understood - that DNOs regard those figures as the maximum they should supply, and that (whether they are legally obliged to or not) they always act to achieve that if higher figures are reported to them - and I have never heard of a case in which they 'refused' to improve an earth which had a Ze greater than those figures..

Kind Regards, John

 

[Murdochcat]

ITo be clear, my comment was not a general one, but one which related specifically to the OP's situation -in which we know that the Ze must be appreciably less than 1.19Ω. As I've said, you may disagree with my word "significantly", but I certainly would not regard a figure of 'appreciably less than 1.19Ω" as being 'very high' (in relation to thee 0.8Ω figure), would you?

Kind Regards, John

But we have no idea what the Ze is as it hasn’t been properly tested

 

[JohnW2]

But we have no idea what the Ze is as it hasn’t been properly tested

"No idea" is an exaggeration.

As I wrote (in what you quoted) we know that the Ze is "appreciably lower than 1.19Ω", which I would say is a lot more than "no idea" - and if the OP could give us an estimate of the length of the (I imagine 6mm²) circuit, we could provide a much closer estimate of his Ze than tha.

 

[justanotherguy]

"No idea" is an exaggeration.

As I wrote (in what you quoted) we know that the Ze is "appreciably lower than 1.19Ω", which I would say is a lot more than "no idea" - and if the OP could give us an estimate of the length of the (I imagine 6mm²) circuit, we could provide a much closer estimate of his Ze than tha.

The kitchen was installed before I bought the place.

Given where the isolator (if that’s the right word?) is opposite side to the hob I’d say 10 to 11 metres.

 

[JohnW2]

The kitchen was installed before I bought the place. Given where the isolator (if that’s the right word?) is opposite side to the hob I’d say 10 to 11 metres.

OK. Thanks.

By my reckoning,10 metres of 6mm² cable (if that's what it is) would have an "R1+R2" (resistance of line plus earth) of about 0.127Ω, in which case the Zs measurement of 1.19Ω would imply a Ze of about 1.063Ω - which, even though a rough estimate, would seem to be much moire than "no idea"

Kind Regards,John