Now BS7671 says that 1-phase 3-wire is a 2-phase system

[Paul_C]

514.10.1 of both the BRB and BGB (BS7671:2008 and BS7671:2008(2011) respectively) say that a warning label should be used when an enclosure contains a nominal voltage greater than 230V "where such a voltage would not normally be expected". Those emboldened words clearly are open to interpretation, and maybe were not present in earlier editions.

The "where not normally expected" requirement dates back to the 14th edition:

A.17 Every item of electrical apparatus, or enclosure, within which medium voltage exists and where the presence of medium voltage would not normally be expected, shall be so arranged that before access is gained to live parts, a warning of the maximum voltage present is clearly visible.

As I've just noted with the older definitions elsewhere, medium voltage at that time was defined as being between 250 and 650V. As you say, "not normally expected" is somewhat open to interpretation: Normally expected by whom? You or I might look at the main switchgear for the supply to a larger house and by the nature of that equipment recognize the supply type and thus expect to find 415 or 480V inside. The average householder, not being aware of such things, might "expect" it to be only 240V since that's what he knows he gets from his socket outlets.

The equivalent provision in the 13th edition did not contain the "not normally expected" clause, and required the warning notice in all cases, with a fairly extensive note added to emphasize the point:

109For compliance with Regulation 11 of Part I, terminals and other fixed live parts on which a voltage exceeding low voltage (250 volts) between conductors or to earth may be present shall conform with the requirements of of one of the following clauses (A) or (B), subject to the exemption given below:

(A) They shall be installed in a locked room accessible only to authorized personnel; or

(B) They shall be so enclosed in earthed metal or incombustible insulating material that ready access cannot be had. Unless the points between which a voltage exceeding 250 volts may be present are 6 feet or more apart, means of access shall be marked to indicate the voltage present.

Exemption.- Cables and bare conductors installed in accordance with the requirements of Section 2.

NOTE.- The above requirements apply equally to three-phase circuits in which the voltage between lines or to earth exceeds 250 volts and to groups of two or more single-phase circuits, between which medium voltage may be present, derived therefrom. They apply also to 3-wire d.c. or 3-wire single-phase a.c. circuits in which the voltage between lines or to earth exceeds 250 volts and to groups of 2-wire circuits, between which medium voltage may be present, derived therefrom.

And while on the 13th edition, the requirement about sockets being on the same phase or pole in one room at that time gave a specific floor area of 500 sq. ft. or greater for the exemption to apply.

There are also two differences in 514.10.1 between BRB and BGB:

• 1...In the BGB, "230 volts" has been changed to "230 volts to earth"

• 
  I don't have a copy of either the original 17th edition or the new amendment. What's the context in which that appears?
  
  

  2...To my surprise, the second and third paragraphs of 514.10.1 have disappeared in the BGB. This means that there is no longer a need for warning signs when 'nearby' (can be simultaneously reached) separate enclosures contain voltages >230v relate to one another

  
  Now you quote that, I think it was mentioned on the IET forum a few weeks ago. So that's another relaxation of a long-standing requirement. I wonder if that was done as another part of the "harmonization" process with European standards, since it's long been the norm to have 3-phase supplies in domestic properties in many Continental countries, and seemingly without any of the specific requirements we've had regarding warnings and separation of phases between sockets.
  
  I think the "only one phase for sockets in one room" rule has already gone from BS7671, hasn't it?

 

[JohnW2]

As you say, "not normally expected" is somewhat open to interpretation: Normally expected by whom? You or I might look at the main switchgear for the supply to a larger house and by the nature of that equipment recognize the supply type and thus expect to find 415 or 480V inside. The average householder, not being aware of such things, might "expect" it to be only 240V since that's what he knows he gets from his socket outlets.

Exactly. It was also clearly deliberately introduced, but I would say that it does anything but 'clarify' the regulation.

There are also two differences in 514.10.1 between BRB and BGB:

• 1...In the BGB, "230 volts" has been changed to "230 volts to earth"

• I don't have a copy of either the original 17th edition or the new amendment. What's the context in which that appears?

• 
  Sorry; I assumed you had it. That's simply the requirement for a warning label when voltages >230v are present in an enclosure when 'not normally expected'.
  
  Without thinking too much, I originally thought that adding 'to earth' had little effect. However, now I've thought, it's clearly a major relaxation, which I presume has effectively removed the need for any 'voltage warning notices' in an installation running from a 3-phase 230/400V supply - since, whilst 400V exists between phases, there should be no voltages 'to earth' which exceed a nominal 230V.
  
  

  Now you quote that, I think it was mentioned on the IET forum a few weeks ago. So that's another relaxation of a long-standing requirement. I wonder if that was done as another part of the "harmonization" process with European standards, since it's long been the norm to have 3-phase supplies in domestic properties in many Continental countries, and seemingly without any of the specific requirements we've had regarding warnings and separation of phases between sockets.

  Quite probably. 'Harmonisation' often seems to have the effect of reducing everyone to the lowest level (of safety in this case)!
  
  

  I think the "only one phase for sockets in one room" rule has already gone from BS7671, hasn't it?

  sensible though it would be, I can't say I've seen such a restriction (anyone?), so you're probably right. Indeed, in the original BS7671:2008, 514.10.1 required warning labels if things with a >230v pd between them could be touched simultaneoulsy - so presumably that degree of proximity was allowed - and, as I said above, even the requirement for that warning label has now vanished in the amendment.
  
  So, as above, it seems that we may now have reached the ultimate in 'relaxation' as regards 'voltage warning labels' - since it looks to me as if they are now not required unless one has a supply higher than 230/400V.
  
  Kind Regards, John.

 

[Paul_C]

Sorry; I assumed you had it.

Never had any need for it, and better things to spend the money on.

Without thinking too much, I originally thought that adding 'to earth' had little effect. However, now I've thought, it's clearly a major relaxation, which I presume has effectively removed the need for any 'voltage warning notices' in an installation running from a 3-phase 230/400V supply - since, whilst 400V exists between phases, there should be no voltages 'to earth' which exceed a nominal 230V.

And, as per the original topic of this thread, the same for the 3-wire system with a nominal official voltage between poles now of 460V (in reality still nominally 480V, and up to slightly over 500V at the high end of the permitted tolerance).

We seem to have come a long way from when the regs. required all enclosures in which anything over 250V is present to be marked with the voltage to this new version which appears not to require any notices at all for systems in common use which can be, in effect, up to 500V.

Quite probably. 'Harmonisation' often seems to have the effect of reducing everyone to the lowest level (of safety in this case)!

Definitely!

So, as above, it seems that we may now have reached the ultimate in 'relaxation' as regards 'voltage warning labels' - since it looks to me as if they are now not required unless one has a supply higher than 230/400V.

Or 230/460V (officially).

 

[JohnW2]

We seem to have come a long way from when the regs. required all enclosures in which anything over 250V is present to be marked with the voltage to this new version which appears not to require any notices at all for systems in common use which can be, in effect, up to 500V.

So it seems, but I'm certainly ignoring these 'advances'. In my home, although there are very few left, any enclosures containing two or more phases, and any pairs of enclosures on different phases within reaching distance of one another, will continue to bear 'appropriate' warning labels for as long as I have anything to do with it!

These apparantely retrogressive changes (safety-wise) in BS7671 might be another bit of ammunition for the defence in the hypothetical court case we've been discussing - since it would be a good illustration for the court that the most recent version of BS7671 is by no means necessarily the version which specifies the most safe practices!

So, as above, it seems that we may now have reached the ultimate in 'relaxation' as regards 'voltage warning labels' - since it looks to me as if they are now not required unless one has a supply higher than 230/400V.

Or 230/460V (officially).

I'm not sure you mean there. I was referring to the 'standard' 3-phase supply, with each phase nominally 230v from neutral and nominally 400v (fractionally under) between phases.

Kind Regards, John.

 

[radweld]

In my home, although there are very few left, any enclosures containing two or more phases, and any pairs of enclosures on different phases within reaching distance of one another, will continue to bear 'appropriate' warning labels for as long as I have anything to do with it!

Fair enough - but can you give an example of something you wouldn't do as a result of seeing such a warning label? (which - if you assume the max potential is 'only' 230v you'd have been quite happy to have done). Thinking about it, I'm struggling to actually see the benefit of such a warning label.

 

[Paul_C]

I'm not sure you mean there. I was referring to the 'standard' 3-phase supply, with each phase nominally 230v from neutral and nominally 400v (fractionally under) between phases.

I just meant that this relaxed requirement means not only that a 3-phase system with 400V present does not need labeling, but that the single-phase 3-wire system we've been debating in which there is an even higher voltage of 460V between poles doesn't either.

 

[JohnW2]

I'm not sure you mean there. I was referring to the 'standard' 3-phase supply, with each phase nominally 230v from neutral and nominally 400v (fractionally under) between phases.

I just meant that this relaxed requirement means not only that a 3-phase system with 400V present does not need labeling, but that the single-phase 3-wire system we've been debating in which there is an even higher voltage of 460V between poles doesn't either.

Ah, OK - thanks for clarifying.

Kind Regards, John.

 

[Paul_C]

Fair enough - but can you give an example of something you wouldn't do as a result of seeing such a warning label? (which - if you assume the max potential is 'only' 230v you'd have been quite happy to have done). Thinking about it, I'm struggling to actually see the benefit of such a warning label.

Maybe it's really of more benefit to the casual layman who might otherwise think that because he's changed a light pendant and wired a 13A socket he can do anything which is "only" 230 volts? But then I suppose that comes back to the earlier question about whether a higher voltage would "normally be expected" or not.

 

[JohnW2]

In my home, although there are very few left, any enclosures containing two or more phases, and any pairs of enclosures on different phases within reaching distance of one another, will continue to bear 'appropriate' warning labels for as long as I have anything to do with it!

Fair enough - but can you give an example of something you wouldn't do as a result of seeing such a warning label? (which - if you assume the max potential is 'only' 230v you'd have been quite happy to have done). Thinking about it, I'm struggling to actually see the benefit of such a warning label.

A good point. For a start, it wouldn't be for my benefit - since I know what's inside all the enclosures! When I spoke of 'appropriate warning labels', I suppose I was thinking more of situations in which there was not a single point of isolation for everything within the enclosure - which, 'co-incidentally' (in my home) only arises in the rare situations in which 2 or 3 phases (hence pds of 400v) are present within the same enclosure. The requirement for such an 'isolation' warning still exists in 514.11.1 of the BGB - and I suppose it's actually that which matters, not the voltage. As you say, there is nothing I would or would not do differently depending on whether an enclosure contained voltages (relative to earth) or pds of 230v or 400v.

Kind Regards, John.

 

[Paul_C]

Couldn't it be said that the vast majority of warning notices - electrical or any other type - are there mostly for those who are not familiar with whatever it is he may be sticking his fingers into?

We don't really need to be told that a 3-phase enclosure has 415V present inside it, because we know what to expect in that type of enclosure. The casual observer sees just "an electrical box" and might think that it's 240V because that's all he knows about the power provided by the sockets in his home.

A chemist looking at a bottle labeled HNO3 or H2SO4 understands that the contents are harmful. The layman, or at least the person who knows no basic chemistry, will understand far more from a warning which says "Danger - Acid." And so on for almost any field.

 

[JohnW2]

Couldn't it be said that the vast majority of warning notices - electrical or any other type - are there mostly for those who are not familiar with whatever it is he may be sticking his fingers into? We don't really need to be told that a 3-phase enclosure has 415V present inside it, because we know what to expect in that type of enclosure. The casual observer sees just "an electrical box" and might think that it's 240V because that's all he knows about the power provided by the sockets in his home.

Yes, one imagines that's a major part of the thinking - but, as radweld said, does it really make that much difference to the 'casual observer' whether (s)he sticks his/her finger into a enclosure containing 240v or 415v (or '230v or 400v' )?

The 'warning label' which almost embarrasses me everytime I see it is the one about 'colours according to two versions of BS7671'.

Kind Regards, John.

 

[ban-all-sheds]

Why does that embarrass you?

 

[JohnW2]

Why does that embarrass you?

Because no-one who is even vaguely thinking about doing anything to an electrical installation should need telling about the old and new colours, or the need to 'carefully identify conductors' when both old and new colours are present.

Put another way, if one really thought that it was necessary to display warning labels to cater for for people who were working on an electrical installation wiring without knowing about the two sets of colours, one really would need to add another '999' labels to tell them everything else they would need to know before tackling such work!

Kind Regards, John.

 

[Paul_C]

The precise wording could also be considered a little strange because anyone who knows what BS7671 is will almost certainly already understand about the two different schemes. Anyone reading that label who doesn't already understand the implications of there being two different schemes in use will likely have no idea what the reference to BS7671 means. So why include the reference to BS7671 at all?

"Warning: This installation contains wiring to two different colour code standards," would suffice, would it not, if it's considered necessary to warn at all? Even more useful for the uninitiated would be if the label actually noted the corresponding colors for each scheme. But as you say, just how far should one go in plastering labels over everything to explain what's going on?

It's noteworthy that this is the first such label to be specified by the regs., despite there having been several changes in parts of the color code in the past.

 

[Paul_C]

in the rare situations in which 2 or 3 phases (hence pds of 400v) are present within the same enclosure.

Speaking of which, and prompted by a question in another thread about multi-gang light switches on more than one circuit, does the current version of BS7671 still require a screen or barrier between different sections of a multi-gang switch on different phases?