BS7671:2008(2015) - Cmin=0.95 and no other obvious surprises

[EFLImpudence]

Could it just be that the price is excessive?

 

[ban-all-sheds]

There is an element of that. I suggest that were it £7.50 and not £75 this topic would not be discussing price, whether it should be an amendment or not, etc.

Anybody know how it compares to the US or Canadian NEC, NF C 15-100, DIN VDE 0100, for example?

 

[scousespark]

The issue of price comes up every time there is a change. If you take the price as a one-off, it is around the price of a drill battery. Spread over the time between printed amendments, it's around the price of a cable cutter.

For a diyer, this is a hobby purchase. If you object to the price, don't buy a copy.

 

[JohnW2]

There is an element of that. I suggest that were it £7.50 and not £75 this topic would not be discussing price, whether it should be an amendment or not, etc. ...

I'm sure that's right.

Anybody know how it compares to the US or Canadian NEC, NF C 15-100, DIN VDE 0100, for example?

I don't know, but what I do know is that one doesn't get much in the way of technical/specialised documentation of this sort for a lot less than £75 these days - it's obviously different from a popular novel written by someone on their kitchen table, both in terms of the cost of production and the potential market size. Putting BS7671 in context, AFAIA, as the cost of British Standards go, £75 is towards the bottom of the range of prices.

As I've said before, if the industry had government-imposed/legislated regulations (rather than relying on documents produced by other organisations), access to them would probably/presumably be without cost.

Kind Regards, John

 

[JohnW2]

The issue of price comes up every time there is a change. If you take the price as a one-off, it is around the price of a drill battery. Spread over the time between printed amendments, it's around the price of a cable cutter.

Indeed.

For a diyer, this is a hobby purchase. If you object to the price, don't buy a copy.

Very true. However, interestingly, at least some (possibly all) of those who have commented in this thread about price have been practising electricians. At the very least, the cost of purchasing the regs is tax-deductible for them.

Kind Regards, John

 

[westie101]

So we have around 100 Codes of Practice that are constantly being amended, now apart from on-line access they are all issued as loose leaf A3 or A4 folders, so if an amendment is released we only receive the relevant pages and change them.

The airline industry with all it's safety documentation does the same.

Put this is how industry works to contain costs and act sensibly, oh hang on BS7671 is issued by an industry body that seems unbothered by other's costs.

 

[scousespark]

In particular, as rather expected, the value of "Cmin" remains as 0.95, despite the suggestion from myself and others that, in view of range of permitted UK supply voltages, 0.94 would perhaps be more logical. However, it may not be 'their fault'- it seems that the value of "Cmin" is probably defined by "PD CLC/TR 50480", whatever that may be.
Kind Regards, John

The CLC is CENELEC, which is the body responsible for setting the electrical standards across the EU. They have determined the value for Cmin. I have no idea what calclulations or experiments were used to derive this value and don't really need to know. It is the value we will apply going forwards.

Do you really believe the JPEL were at fault for not taking your suggestion (should that be demand) to change Cmin to 0.94, but you are excusing them because the blame for this appears to lie with CENELEC?

 

[JohnW2]

In particular, as rather expected, the value of "Cmin" remains as 0.95, despite the suggestion from myself and others that, in view of range of permitted UK supply voltages, 0.94 would perhaps be more logical. However, it may not be 'their fault'- it seems that the value of "Cmin" is probably defined by "PD CLC/TR 50480", whatever that may be.

The CLC is CENELEC, which is the body responsible for setting the electrical standards across the EU.

Thanks.

They have determined the value for Cmin. I have no idea what calclulations or experiments were used to derive this value and don't really need to know. It is the value we will apply going forwards.

It is obviously true that this is the value we are going to have to use in the future. I was just a little surprised that, having introduced what I personally regard as a very sensible change in the right direction, they stopped just slightly short of a regulation which would guarantee that all (not just most) installations would meet their own disconnection time requirements. As you say, CENELEC must have had a reason for their choice of 0.95, but I'm not sure that it does (or should) require any "calculations or experiments" - one merely needs to look at the permitted range of supply voltage variation to see the point which I (and others) were making. It's a pretty minor issue, since I very much doubt that many installations have a supply voltage less than 218.5V, but it still does not seem to be very logical in engineering (or 'safety') terms.

Do you really believe the JPEL were at fault for not taking your suggestion (should that be demand) to change Cmin to 0.94, but you are excusing them because the blame for this appears to lie with CENELEC?

I'm not saying that anyone is/was "at fault". When I submitted my suggestion, I was told that, even though my submission was slightly late, it would normally have been passed on to the committee, but they were not going to bother because "so many other people had already made the same suggestion". I was therefore far from alone. What I (and probably the others who had made the same point) didn't know is that it seems that JPEL's hands were probably already tied by what CENELEC had dictated.

Kind Regards, John

 

[westie101]

It's a pretty minor issue, since I very much doubt that many installations have a supply voltage less than 218.5V, but it still does not seem to be very logical in engineering (or 'safety') terms.

Though if CENLEC is involved is it not a case for whatever reason to striving for an EU wide figure. Given that on the continent 230V -10% (220V-6%) is acceptable how does that match up?

 

[JohnW2]

It's a pretty minor issue, since I very much doubt that many installations have a supply voltage less than 218.5V, but it still does not seem to be very logical in engineering (or 'safety') terms.

Though if CENLEC is involved is it not a case for whatever reason to striving for an EU wide figure. Given that on the continent 230V -10% (220V-6%) is acceptable how does that match up?

Interesting point - but that, of course, would make it 'worse' in continental Europe - if 230V - 10% is permitted, then one would need Cmin=0.90 (rather than 0.95 or 0.94) for calculations to properly 'cover' installations with all permitted supply voltages.

One can but speculate, but one suspects that the 0.95 figure may well be statistically derived - i.e. relating to supply voltage below which only some small percentage (5%, 2%, 1%??) of installations will receive. However, implicit in that approach is that calculations based on that value could leave some of that small percentage of installations without the required disconnection times. Perhaps that is regarded as 'acceptable'.

Kind Regards, John

 

[scousespark]

So we have around 100 Codes of Practice that are constantly being amended, now apart from on-line access they are all issued as loose leaf A3 or A4 folders, so if an amendment is released we only receive the relevant pages and change them.

The airline industry with all it's safety documentation does the same.

Put this is how industry works to contain costs and act sensibly, oh hang on BS7671 is issued by an industry body that seems unbothered by other's costs.

If BS7671 was being amended continuously I would expect amendments to be issued as above. Given the combined cost of the Regs, GN3 and the OSG will be less than £150 and change every few years, we are hardly being ripped off. Compare this cost with scheme membership or LABC notification charges. As John has stated, BS7671 is at the low end of the charging scale for British Standards.

 

[scousespark]

It's a pretty minor issue, since I very much doubt that many installations have a supply voltage less than 218.5V, but it still does not seem to be very logical in engineering (or 'safety') terms.

Though if CENLEC is involved is it not a case for whatever reason to striving for an EU wide figure. Given that on the continent 230V -10% (220V-6%) is acceptable how does that match up?

We are talking Europe here and everything takes time. Think how long it took for the cable colour changes. and then think of the individual distribution/supply characteristics across the EU. Harmonisation will be continuing well into the future.

 

[scousespark]

John

I posted my question regarding fault as you stated you didn't see them at fault for not adopting the 0.94 value which you wanted them to use.

In a simplistic sense as we allow -6% to + 10% the 0.94 seems logical. As I said, the 0.95 value applies across the EU and I have no idea what it is based on. If you want to see the calculations and have a spare £200 you can buy a copy of the document.

 

[JohnW2]

John I posted my question regarding fault as you stated you didn't see them at fault for not adopting the 0.94 value which you wanted them to use.

I'm sure you understood what I meant. I was using "their fault" colloquially and, indeed, put it in quotes ...

However, it may not be 'their fault'- it seems that the value of "Cmin" is probably defined by "PD CLC/TR 50480", whatever that may be.

I was merely saying that their hands were probably tied by what CENELEC had dictated.

In a simplistic sense as we allow -6% to + 10% the 0.94 seems logical.

Exactly my point (and semingly the view of many others) - no more, and no less, than that!

As I said, the 0.95 value applies across the EU and I have no idea what it is based on. If you want to see the calculations and have a spare £200 you can buy a copy of the document.

Indeed. As I wrote in response to westie, I suspect that it's probably a statistically-derived figure, designed to ensure that the majority (but not all) installations are 'safe'. If that is the case, then opinions will probably vary as to how reasonable an approach that is. If there were no absolute minimum supply voltage specified, then such an approach would be inevitable, but that isn't the situation.

Whatever, as you've said, we are stuck with 0.95 for at least a good while. Not only will that deviation from 0.94 only 'affect' a very small number of installations but, as has been discussed here, Zs will rarely be sufficiently marginal that it would be an issue even if supply voltage were <218.5V. It's therefore a very minor issue - but I don't really like things which appear illogical If national regulations in those countries do the same, it may, of course, be much more of a potential issue in those European countries in which supply voltage is permitted to be as low as 207V (230V - 10%).

Kind Regards, John

 

[flameport]

Anybody know how it compares to the US or Canadian NEC, NF C 15-100, DIN VDE 0100, for example?

The USA equivalent is around $100
http://www.amazon.com/gp/offer-listing/1455906727/
A fair number of the reviews complain about the price.