Max Zs on certification

[Dan007]

Please can people clarify what value they insert in the Max Zs field on certification.

I've always input 100%. Currently in disagreement with another person as they are specifying 80%.

Done my 2391 in 2008 and I was taught and told it's always 100% and it's down to the QS to interpret the results and ensure they fall with 80% allowing for correction factors.

Third argument is that in GN3 and OSG they specifically state 80% - however I always understood these to be quick reference pocket guides while on site.

In the mentioned publications and BBB the model forms show 100% in the compelte fields for examples. Secondly the small print at the bottom makes reference to the Publication and values in Chapter 41 aka BBB and 100% values.

Your thoughts please people

 

[Rodders099]

An. Interesting debate so far ....

How about the certificate having tick boxes for 100% and 80%

tin hat on ....

Would never happen....because the iet decide on these things and don’t see it as something they need to introduce to the form.
The NICEIC love to make their own stuff up, to somehow seem regulatory.

If this issue was in any way important....it would have been changed to a mandatory requirement.

 

[westward10]

Essex.....really??? It would need looking at ??
And where does it say that, what code would you use and who is going to pay for your non-regulated investigation ???

Edited to add, I know exactly where the 80% comes from.

I think you are misreading what @essex is quoting.

 

[Nigel]

seriously though....your in a 5 bed house over 3 floors.
Max Zs for 32a ring is 1.37. 80% is 1.1
You record 1.20.
What exactly are you going to do about this ???
I’m going to do nothing.....record 1.20 on the EICR,
and carry on.

That would then mean you are doing an EICR incorrectly.

It is debatable if it is a C2 or a FI but it is an ‘unsatisfactory’ all the same.

 

[Rodders099]

That would then mean you are doing an EICR incorrectly.

It is debatable if it is a C2 or a FI but it is an ‘unsatisfactory’ all the same.

And still I’ve had no reply to my question.....which BS1761 reg are you attaching to your C2 or FI decision ???

 

[Silly Sausage]

An. Interesting debate so far ....

How about the certificate having tick boxes for 100% and 80%

tin hat on ....

Just write 100% above any Zs columns, sorted

 

[Zdb]

Always the 100% values for me. The NICEIC inspector insists upon it.

 

[Nigel]

I’m seriously confused here......you’d investigate what and whose orders ??
Your in for an EICR, the Cert asks for MAX Zs.
What code are you going to give a 1.20zs on a 32a ring like in my example above ??
Then, how are you going to explain to the person requesting the EICR that further time...possibly hours, is required for investigating.....even though your recorded results satisfy the cert ??
Finally, which regulation are you quoting to the customer....which justifies your advice for further investigation ??
I’m all ears guys.......I’d love the extra work I could self generate by going down this road.....

I would not investigate anything without the permission of the person responsible for paying. What I would do is one of two things:

1. Mark it on the EICR as ‘FI’ and then submit the report if I felt loose connections could be the cause.

2. Mark it as a C2 as the OCPD would not operate in time which is a direct non-conformance to BS7671. I have not got the book in front of me. Maybe someone se can help.

We do not carry out periodic insepctions to ‘satisfy the cert’. We carry out periodic inspections to issue a report based on BS7671.

I would just use BS7671 to justify any issues I found.

 

[Nigel]

noones answering my questions.......how you gonna convince the customer, that although your results meet the certs requirements......you still need further investigation.
And which code and which reg are you gonna quote ??
This is the minimum info that would be required in order to carryout further investigation.

I do not need to convince anyone. My qualifications and 20 years experience should speak for themselves. Couple that with a quote from BS7671 and then it is up to the customer to decide what they want to do.

 

[Nigel]

Is there an RCD or RCBO fitted to the circuit? Or are we talking old 3036 dinosaur wiring etc. I've been to plenty of new installs where the Zs is oitsido of Zs parameters but protected mechanically. Not much we can do here. Down to poor design really.

In this instance I woukd record the max Zs permitted as 1667 if the RCD is 30mA.

 

[Nigel]

its not that I entirely dismiss the 80% thing or don’t see the vague point.....it’s more that I can’t see how I explain to a customer that although my tests say it’s ok and it’s below the value stated in the regs, I’m going to code it and recommend potentially costly further investigation......which I’d struggle to justify with a clear reg.

You need to get past thinking your test results say it is ok. They are not.

 

[Rodders099]

Fair enough Essex...I’m not actually saying your wrong or that your not experienced or criticising how you operate.
I was asking for reasoning as to how I would justify to a customer that FI was required at possibly considerable cost....for something which I couldn’t back up with a reg.

I strongly disagree that a measured figure below the tabulated Max Zs in the BS1761 would ever be a C2 though.

 

[Nigel]

An. Interesting debate so far ....

How about the certificate having tick boxes for 100% and 80%

tin hat on ....

Why?

 

[Nigel]

Fair enough Essex...I’m not actually saying your wrong or that your not experienced or criticising how you operate.
I was asking for reasoning as to how I would justify to a customer that FI was required at possibly considerable cost....for something which I couldn’t back up with a reg.

I strongly disagree that a measured figure below the tabulated Max Zs in the BS1761 would ever be a C2 though.

Are you suggesting an OCPD not operating on time is not against BS7671?

How long is it really going to take to check connections? I would actually only do this on a borderline case. If it was way over I would quote to install an RCD as fault protection.

What code would you recommend for an OCPD not operating in time?

 

[Nigel]

And still I’ve had no reply to my question.....which BS1761 reg are you attaching to your C2 or FI decision ???

I don’t have the book at the moment.

 

[Rodders099]

Are you suggesting an OCPD not operating on time is not against BS7671?

How long is it really going to take to check connections? I would actually only do this on a borderline case. If it was way over I would quote to install an RCD as fault protection.

What code would you recommend for an OCPD not operating in time?

But it is operating in time.....the measured Zs of my example of 1.2 on a 32A ring circuit....is below 1.37 Max Zs required to make it operate on time.