High Zs values (Just)

[Deleted member 9648]

Given that Amd3 reduced max Zs values slightly what is everyone coding if a measured reading falls between the pre Amd3 value and the post Amd3 value. Failure to meet disconnection times would normally be a code 2, but a code 3 seems appropriate here......maybe a note to explain? On E-certs it will show a measured reading exceeding the maximum value given in the schedule.
Just seems silly that not long back a reading met disconnection times and now it doesn't, nothing has actually changed.

 

[Intoelectrics]

I have not actually come across this yet, though it has been close at times. If this were found then I would expect that some careful retermination of connections would resolve the problem, you are talking a fraction of an ohm here.
Unfortunately with circuit breakers if the resistance level were exceeded then the disconnection time could jump from practically instantaneous up to 13s (if the circumstances were just right, the type B CB is on the upper limit of design(5In) and the supply voltage is down to 218V) this tends to mean that non compliance could be significantly dangerous, though as you say it was deemed safe three years ago, only the definition of dangerous has changed.
If it were a fuse then a faction of an ohm increase would not significantly increase the danger as the time would be 0.401s instead of 0.4s and this might be suitable to be coded as improvement recommended. I think (silly as it sounds) if it is a circuit breaker then a potentially dangerous situation by the new definition of dangerous is now in place.

As you stated if the readings are very close to the stipulated maximum values then it could be just a matter of checking the terminations at accessories. I have had this situation many times especially on RFCs, which can flag up when you do end to end measurements and you get high or inconsistent readings. Many times it has turned out to be a loose connection or a poorly terminated conductor.
I think "wirepuller" is in a tricky spot as he has to explain to the client that prior to AMD3 there was no problem but now it doesn't comply. Then explaining to the client that the installation is potentially dangerous will be awkward also because they will likely not understand how it can be completely safe a few years back but now dangerous, yet there have been no alterations or deterioration?
Electricians these days have to be highly skilled consultants, negotiators, teachers and salespersons.

 

[Intoelectrics]

Duplicate post

 

[telectrix]

so, this Cmin. causes problems. samewith the temp.0.8. never ever seen a supply voltage as low as 218V, never seen a cable reach 70 deg.Cunless overloaded.just justification for the IET trough feeders high earnings.

 

[Ian1981]

so, this Cmin. causes problems. samewith the temp.0.8. never ever seen a supply voltage as low as 218V, never seen a cable reach 70 deg.Cunless overloaded.just justification for the IET trough feeders high earnings.

I think the point is that it could happen.
Cables designed for maximum operating temperature of 70 degrees can be allowed to reach this temperature and thus allowances must be made for this scenario.
The voltage matter......same as you never recorded at voltage so low before but again it’s erring on the side of caution and above all else, safety

 

[Deleted member 9648]

It will be in harder to explain why you think you can just ignore parts of BS7671.

Maybe he will write down that it is only just a little bit dangerous.

Not all non-compliances with current 7671 will attract a code 2. For example the recommended code for a cable buried at <50mm deep without RCD protection and compliant with recent previous editions of 7671 is a code 3.
That's not 'ignoring' BS7671, it is recognising that while it does not comply with the latest edition, it complied with a recent but previous edition and was deemed safe then so cannot suddenly be dangerous.
If your logic applied then any code 3 would be 'ignoring' Bs7671, there would only be a code 1 or 2 permitted.

 

[Nigel]

Not all non-compliances with current 7671 will attract a code 2. For example the recommended code for a cable buried at <50mm deep without RCD protection and compliant with recent previous editions of 7671 is a code 3.
That's not 'ignoring' BS7671, it is recognising that while it does not comply with the latest edition, it complied with a recent but previous edition and was deemed safe then so cannot suddenly be dangerous.
If your logic applied then any code 3 would be 'ignoring' Bs7671, there would only be a code 1 or 2 permitted.

You understanding of a C3 is not correct I am afraid.

 

[Ian1981]

Thing is we are required to inspect and test to the current edition of the wiring regulations and for us to achieve ADS as well as the protective bonding to be in place, then the formula
Zs x Ia must be equal to or less than 230v x cmin (0.95).
If the circuit(s) can’t fulfill that formula then I can only see a C2 option as ADS can not be guaranteed at all times, at least not according to bs7671.

 

[Deleted member 9648]

You understanding of a C3 is not correct I am afraid.

Kindly explain it to me then.

 

[davesparks]

Not all non-compliances with current 7671 will attract a code 2. For example the recommended code for a cable buried at <50mm deep without RCD protection and compliant with recent previous editions of 7671 is a code 3.

Compliance with previous editions, recent or not, does not affect the code given.
The code given is in accordance with the current edition.

 

[davesparks]

so, this Cmin. causes problems. samewith the temp.0.8. never ever seen a supply voltage as low as 218V, never seen a cable reach 70 deg.Cunless overloaded.just justification for the IET trough feeders high earnings.

Out of interest how often have you measured the temperature of the conductors within a cable in service?

 

[telectrix]

not often. last time was a 16mm T/E running @ 100A. it reached 40 deg.C. after 30 minutes when the 63A MCB tripped. that's the sheath temp, conductors probably a bit warmer.

 

[davesparks]

not often. last time was a 16mm T/E running @ 100A. it reached 40 deg.C. after 30 minutes when the 63A MCB tripped. that's the sheath temp, conductors probably a bit warmer.

Exactly, not often, hardly a good sample size to make a conclusion about every cable in every installation in the country.

 

[Intoelectrics]

Exactly, not often, hardly a good sample size to make a conclusion about every cable in every installation in the country.

I have often come across cables that are worryingly hot during normal service. Though I have not actually measured the temperature of many some have been too hot to touch. I'd say (depending on the install) temperature is a very serious factor to consider when doing an install.

 

[telectrix]

Exactly, not often, hardly a good sample size to make a conclusion about every cable in every installation in the country.

i agree, mainly in industrial situations, but generally, cables are underrated by the BS7671 to err on the side of safety, espin the domestic sector where cables are rarely pushed anywhere near their rated capability.

 

[Deleted member 9648]

Not all non-compliances with current 7671 will attract a code 2. For example the recommended code for a cable buried at <50mm deep without RCD protection and compliant with recent previous editions of 7671 is a code 3.

Compliance with previous editions, recent or not, does not affect the code given.
The code given is in accordance with the current edition.

The post you have quoted clearly states that codes are allocated according to the current edition of 7671, I have not suggested otherwise.
But my interpretation of a code 3 issue is one that does not comply with current 7671 but in the opinion of the inspector does not compromise the overall safety of the installation. I'm still waiting for Essex to explain his interpretation to me.
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.

 

[plugsandsparks]

It clearly isn't dangerous and i am at a loss understanding the need to introduce it, there is obviously a downside as cabling and distribution costs will obviously rise, breakers will be much more on the limit of the load and may cause nuisance tripping, so balance this against an install that might only have 220V and simultaneously have a short cct fault. 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.

 

[Nigel]

The post you have quoted clearly states that codes are allocated according to the current edition of 7671, I have not suggested otherwise.
But my interpretation of a code 3 issue is one that does not comply with current 7671 but in the opinion of the inspector does not compromise the overall safety of the installation. I'm still waiting for Essex to explain his interpretation to me.
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.

It is really very simple. A c3 is an issue that is not dangerous if left but could be improved using the current Edition of 7671 as a guide.

So anything that is not done to 7671 but is not classed a C1 or a C2 would be a C3.

 

[Deleted member 9648]

Er...that explanation looks pretty much the same as mine

 

[Nigel]

Er...that explanation looks pretty much the same as mine

It read as if you were saying if it meets a previuos version of 7671 then you would no code it.

 

[Deleted member 9648]

It read as if you were saying if it meets a previuos version of 7671 then you would no code it.

Ok, wasnt what I meant,

 

[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.