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?

[EFLImpudence]

I'm just wondering if that's the only option right now?

Yes, it is.

 

[JohnW2]

I called UKPN - went as well as I expected. They just redirected me to the form I already told them I'd seen. Computer says no.

It seems fairly unlikely that the DNO-supplied earth is significantly 'high resistance'. A TN-S earth is allowed to have a Ze of up to 0.8Ω - so, unless the cooker circuit is pretty short in length, the measured Ze of 1.19Ω would seem to be quite credible(if the Ze of the DNO earth was close to the 'maximum allowed).

 

[justanotherguy]

It seems fairly unlikely that the DNO-supplied earth is significantly 'high resistance'. A TN-S earth is allowed to have a Ze of up to 0.8Ω - so, unless the cooker circuit is pretty short in length, the measured Ze of 1.19Ω would seem to be quite credible(if the Ze of the DNO earth was close to the 'maximum allowed).

I was going by another response suggesting I just contact the DNO.

The hob installer said only 0.87Ω would be acceptable at the hob connection - so if you're saying 0.8Ω would be ok for Ze, is just 0.07Ω realistically achievable for the connection from CU to hob?

 

[JohnW2]

The hob installer said only 0.87Ω would be acceptable at the hob connection - so if you're saying 0.8Ω would be ok for Ze, is just 0.07Ω realistically achievable for the connection from CU to hob?

Only if the length of the cable from CU to hob is pretty short. Of course,the Ze may bee nowhere near as high as 0.8Ω - that is the theoretical 'maximum'

 

[justanotherguy]

Only if the length of the cable from CU to hob is pretty short. Of course,the Ze may bee nowhere near as high as 0.8Ω - that is the theoretical 'maximum'

In which case I'm not sure where that leaves me - are the installers wrong to not install? Or do 32A hobs just have to be really close to the CU?

 

[EFLImpudence]

In which case I'm not sure where that leaves me -

You need an electrician.

are the installers wrong to not install?

No.

Or do 32A hobs just have to be really close to the CU?

No.

 

[justanotherguy]

I'm trying to reconcile different responses here. Your curt answers are at odds with the more helpful responses.

One person is saying contact the DNO. Another is saying that the required resistance may not even be achievable except with a short cable - meaning kitchens with hobs have to be very near the CU.

You're just saying "no". Super helpful, thanks.

 

[JohnW2]

In which case I'm not sure where that leaves me - are the installers wrong to not install?....

They're not really 'wrong', in that any use of the circuit is theoretically 'not safe' if the Zs is too high.

.... Or do 32A hobs just have to be really close to the CU?

That obviously depends on Ze. With TN-C-S the 'maximum'; is 0.35Ω and, in practice, may well be a lot lower than that-so the situation is therefore then much more manageable. People who sell fairly high-powered electrical appliances don't seem to 'warn' customeers about the potential issues of suitability of their electricity supply.

 

[justanotherguy]

They're not really 'wrong', in that any use of the circuit is theoretically 'not safe' if the Zs is too high.

That obviously depends on Ze. With TN-C-S the 'maximum'; is 0.35Ω and, in practice, may well be a lot lower than that-so the situation is therefore then much more manageable.

But you're saying the DNO can legally leave me in a situation where Ze is 0.8Ω, and therefore mean I can't practically/within safety limits have an induction hob, unless I move my kitchen or CU?

That seems mad to me.

 

[JohnW2]

But you're saying the DNO can legally leave me in a situation where Ze is 0.8Ω, ...

Indeed

and therefore mean I can't practically/within safety limits have an induction hob, unless I move my kitchen or CU?

Even moving your CU would not help, since it's the total cable run back to the DNO's transformer that determines Zs

That seems mad to me.

I understand your frustration,but that's how it is. As I've just written,no-one ever seems to bring this potential problem to the attention of customers.

One can, of course, decrease Zs by changing to an appreciably larger cable - but obviously never to lower than Ze. Also, if a 32A MCB would be adequate,that would allow Zs to be a bit higher

 

[EFLImpudence]

I'm trying to reconcile different responses here. Your curt answers are at odds with the more helpful responses here.

Ok.

One person is saying contact the DNO.

That didn't work, did it?

Another is saying that the required resistance may not even be achievable except with a short cable

He didn't actually say that.
He confused you by saying the maximum allowed is 0.8. Whilst that is true, it is very unlikely to be the case.

- meaning kitchens with hobs have to be very near the CU.

But they aren't and don't have to be, so...

You're just saying "no". Super helpful, thanks.

I only said no when it was the answer to your questions.

I said you need an electrician, which is true and the only way you are going to resolve this matter.

 

[securespark]

It seems fairly unlikely that the DNO-supplied earth is significantly 'high resistance'. A TN-S earth is allowed to have a Ze of up to 0.8Ω - so, unless the cooker circuit is pretty short in length, the measured Ze of 1.19Ω would seem to be quite credible(if the Ze of the DNO earth was close to the 'maximum allowed).

I have to say, in the strongest possible terms, that I strongly disagree with you. I have been called to countless TN-S and TN-C-S supplies where the Ze has been outside the spec, often wildly.

Two of the most memorable were a TN-C-S supply where the reading (if I got one) was 1000+ ohms. There was a bad connection in the cutout.

The other was a TN-S supply where the lead sheath had broken down under the ground and the DNO had to lay a new cable and connect to a sound piece of PILC cable under the pavement.

In this case it looks like a TN-S supply with what looks like an earthing clamp providing the connection to the incoming cable.

It is quite possible that dodgy looking clamp is not doing a good job, hence the raised loop impedance.

The majority of my out of spec Ze readings have been down to such a dodgy connection.

Let's face it, they weren't designed to do that job.

 

[Murdochcat]

Some of your responses have been from retired sparks or diyers

You need a local competent spark - then and only then will you know what to do next

 

[justanotherguy]

I guess I'll just have to get an electrician in - I'm just nervous about what @ericmark said about DNO's required checks:

How? Only way I know what size fuse I have is I was there when new meter fitted. They have seals on them. I have in the past used the enquiry methods to get the Ze, the DNO should have it on record, if not they have to send some one out to measure.

We may be on a ring, (not ring final) and that ring allows sections to be isolated while retaining the supply for work to be carried out, so the Ze can vary depending on if the ring is split or not when the measurement is made. So in theroy the domestic electrician can't work out normal Ze as he has no idea of how supplied when he measures.

So that makes no sense.

So I fear I might pay someone £120 p/h, not agreeing to a fixed price/time, and then them telling me either they can't do the tests required (as @ericmark says), or that they do do the tests and it's a high Ze but still under 0.8Ω (as @JohnW2 said). And then I've spent hundreds and still no closer to just replacing a hob. :sigh:

 

[securespark]

Some of your responses have been from retired sparks or diyers

You need a local competent spark - then and only then will you know what to do next

I'm not incompetent!