High Zs values (Just)

[davesparks]

We are also advised that when carrying out an EICR consideration must be given to the fact that an installation complied with Bs7671 at the time it was installed. For example for an installation wired in the last (say) 20 yrs, lack of RCD protection to socket outlets not likely to supply equipment outdoors would attract a code 3, not a code 2.
I am still not persuaded that a zs reading which was compliant 3 years ago is now potentially dangerous.

Who advises that we should consider whether something complied with the regulations at the time of installation? That is not in bs7671, what is stated in bs7671 is that something installed in compliance with a previous edition but which does not comply now is not necessarily unsafe. Good examples of this are the change in wiring colours or the changes to the wording of labels.

Of those socket outlets now require RCD protection then they should be coded accordingly, the code does not change based on the date of installation.

It is not the case that a Zs reading which complied 3 years ago has suddenly become dangerous, the danger was there 3 years ago but we were not aware of it.

 

[davesparks]

Since i have never measured this voltage on any of the commercial and industrial installation for the last 10 years, i am at a loss to why this obviously costly reg was introduced.

Do you have a written log of every voltage measurement you have made to back this up? And were those measurements taken as instantaneous values or based on logged data over long periods?

Personally I don’t remember ever having measured a voltage below 230V but I have seen it dip on the graphs from data logs though I couldn’t put a numerical value to those dips.

 

[Ian1981]

I don’t think you can use the 3 year date as an excuse really, as in 10 years time it could be in the same state but you can’t say that 13 years ago the zs values complied with an earlier edition of the wiring regulations and not code it as potentially dangerous in my opinion if the stated Zs values ultimately leading to the maximum disconnection times aren’t met.

 

[plugsandsparks]

Do you have a written log of every voltage measurement you have made to back this up? And were those measurements taken as instantaneous values or based on logged data over long periods?

Personally I don’t remember ever having measured a voltage below 230V but I have seen it dip on the graphs from data logs though I couldn’t put a numerical value to those dips.

I dont really need to backup anything, i am stating what i have witnessed, take it or leave it.. on my tester for every loop test i see the voltage and i always clock it in my head to have a guess at the PSSC which i test next, just for a bit of fun. So these are instantaneous, i am more likely to see voltages in excess of 240 than less than 230.
I am talking about 1000s and 1000s of readings over a long period. Where i have logged which is comm and ind, voltage did not move much that i remember

 

[plugsandsparks]

Who advises that we should consider whether something complied with the regulations at the time of installation? That is not in bs7671, what is stated in bs7671 is that something installed in compliance with a previous edition but which does not comply now is not necessarily unsafe. Good examples of this are the change in wiring colours or the changes to the wording of labels.

Of those socket outlets now require RCD protection then they should be coded accordingly, the code does not change based on the date of installation.

It is not the case that a Zs reading which complied 3 years ago has suddenly become dangerous, the danger was there 3 years ago but we were not aware of it.

I dont think the last bit is quite accurate. The danger is not actually there at all and quite frankly its pretty obvious and basic physics that if you lower the voltage disconnection times will increase. Breakers have been designed and now THOSE breakers cannot work correctly at reduced voltages. The manufacturers should change the breaker standards and introduce them over time so as not to cost the whole industry needless money by using thicker cables and more DBs, its total *ollocks / rant off

 

[Deleted member 9648]

Who advises that we should consider whether something complied with the regulations at the time of installation? That is not in bs7671, what is stated in bs7671 is that something installed in compliance with a previous edition but which does not comply now is not necessarily unsafe. Good examples of this are the change in wiring colours or the changes to the wording of labels.

Of those socket outlets now require RCD protection then they should be coded accordingly, the code does not change based on the date of installation.

It is not the case that a Zs reading which complied 3 years ago has suddenly become dangerous, the danger was there 3 years ago but we were not aware of it.

I am loathe to tag your post with a 'disagree'......but I disagree.
Probably no right or wrong on coding here, down to interpretation, and mines different to yours.

 

[westward10]

Why are you so against applying a Code which states fault protection, according to current requirements is not complied with.

 

[Deleted member 9648]

Why are you so against applying a Code which states fault protection, according to current requirements is not complied with.

I have applied a code.....code 3.

 

[delano]

If you take a 32A type B circuit breaker the max Zs under 15th was 1.50 under the 16th the voltage was based upon 230V and was 1.44 now with Cmin reduced further to 1.37 the reduction being 0.13 ohms you can see how this has come about.

It was 1.44 under the 17th as well. Seems like a money making exercise to try and justify buying the amendment 3 books. Now we're expected to fork out again. It's become a joke, a bad one.

 

[westward10]

I have applied a code.....code 3.

What Code do you normally apply for fault protection not being complied with.

 

[telectrix]

to throw the cat into the pigeon coop........ so we are believing that a , say, 0.4 sec. disconnection time cannot be achieved if the Zs of a circuit is a fraction of an ohm above the BS7671 ( corrected, Cmin etc.). who's to say if this is dangerous, or potentially dangerous? how can anyone assume that a person in contact with a "live" exposed part and an extraneous part cannot endure a touch voltage of <50V for a split second longer without dying? have the IET done some tasting on animals to prove or disprove? or is it a case of "let's make something up to justify new regs./amendments?

 

[Toneyz]

Why was this Cmin not come to light years ago it must have always been something to take into account.
You know what will happen next, although in the table it gives maximum Zs values they will write a new reg that states any new circuit must be designed to a max percentage of that to give allowances.

 

[Ian1981]

to throw the cat into the pigeon coop........ so we are believing that a , say, 0.4 sec. disconnection time cannot be achieved if the Zs of a circuit is a fraction of an ohm above the BS7671 ( corrected, Cmin etc.). who's to say if this is dangerous, or potentially dangerous? how can anyone assume that a person in contact with a "live" exposed part and an extraneous part cannot endure a touch voltage of <50V for a split second longer without dying? have the IET done some tasting on animals to prove or disprove? or is it a case of "let's make something up to justify new regs./amendments?

Not sure you can write that on your report tho
If you can’t guarantee the disconnection times quoted by the regulations by using the generic time curves or the manufacturers data for their OCPD’s then you can’t fully comply with the regulations regarding fault protection.

 

[Deleted member 9648]

I'm not going to argue with anyone who advocates a code 2. That's an interpretation which can be justified. But my interpretation is that a compliant circuit is not safe one day and potentially dangerous the next simply because some boff playing with figures moves the goalposts to justify his existence.
However as already stated I will discuss the issue with my NICEIC inspector on his next visit and if he thinks a code 2 is appropriate then that's what I'll do in future...…(through gritted teeth mind you)

 

[Ian1981]

I'm not going to argue with anyone who advocates a code 2. That's an interpretation which can be justified. But my interpretation is that a compliant circuit is not safe one day and potentially dangerous the next simply because some boff playing with figures moves the goalposts to justify his existence.
However as already stated I will discuss the issue with my NICEIC inspector on his next visit and if he thinks a code 2 is appropriate then that's what I'll do in future...…(through gritted teeth mind you)

Keep us updated if you don’t mind if your inspection is anytime soon?
Would be interested to hear another opinion on it

 

[westward10]

Mmm, wonder what this opinion will be

 

[Wilko]

For me it's C2 on a report (sorry). Getting very imaginative - the "fix" could be a temperature and load study proving headroom in the 80% factor, but only in a managed installation. This would then be written onto EIC as a deviation.

 

[Deleted member 9648]

Visits not far away, will update when I get his opinion. I'll wager it'll be a 2.

 

[Ian1981]

Visits not far away, will update when I get his opinion. I'll wager it'll be a 2.

For what it’s worth, I get your point and I don’t want to come over as argumentative.
Just my opinion is all.

 

[Intoelectrics]

to throw the cat into the pigeon coop........ so we are believing that a , say, 0.4 sec. disconnection time cannot be achieved if the Zs of a circuit is a fraction of an ohm above the BS7671 ( corrected, Cmin etc.). who's to say if this is dangerous, or potentially dangerous? how can anyone assume that a person in contact with a "live" exposed part and an extraneous part cannot endure a touch voltage of <50V for a split second longer without dying? have the IET done some tasting on animals to prove or disprove? or is it a case of "let's make something up to justify new regs./amendments?

I did some tasting on a couple of animals last night. I had a chicken and lamb curry, it was delicious.

 

[Deleted member 9648]

I have bowed to the inevitable and issued the EICR with a code 2 for the high Zs. While I still do not agree I've no doubt the NIC will say a code 2 and that seems to be the majority view on here. Remedial will only involve changing a type C for a B, which will no doubt prompt comments about why bother making a fuss. Well I like coding to be correct and justified on my reports regardless of the cost of rectification.

 

[Richard Burns]

I think you are taking the correct action in both cases, code 2 for the New World Order, and feeling that you do not agree but want to get things correct and justified.
The risk assessment would say
Hazard: long disconnection time
Likelihood: 0.0001%, low 1,
Effect: death, high 5.
Risk assessment overall 5, low risk, no action to take, no control measures required.
Overruled by IET random thoughts.
Full control measures to be implemented.

 

[Nigel]

I'm not going to argue with anyone who advocates a code 2. That's an interpretation which can be justified. But my interpretation is that a compliant circuit is not safe one day and potentially dangerous the next simply because some boff playing with figures moves the goalposts to justify his existence.
However as already stated I will discuss the issue with my NICEIC inspector on his next visit and if he thinks a code 2 is appropriate then that's what I'll do in future...…(through gritted teeth mind you)

Why don’t you stick by your guns if you are so certain? What is it about your NICEIC Inspector that you respect so much?

If I was certain of ny stance I would be telling the NICEIC what I am doing not asking them if I can.

 

[Deleted member 9648]

Mostly because inconsistencies in coding is an issue for recipients of EICR's. I think consensus and following established guidelines is important for an EICR to be credible, the worst EICR's I have seen are where the inspector has applied his own prejudices. I recall one where neutrals in a switch box had been given a code 2.