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

[JohnW2]

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?

Quite - and as I wrote in response to BAS, if anyone does need to be told about the colours, then they need to also be told about '999' other things before they should be working on an electrical installation!

Kind Regards, John.

 

[JohnW2]

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?

Understandable though such a requirement might be, I can't recall ever having seen it in 17th edition (anyone?). I also wonder how on earth one would implement it, either with standard plate swtches or grid switches. The actual 'works' of individual gangs of a multigang plate switch, or of separate grid switches (and even the terminals, which are generally recessed within insulating material), are separated by insulating 'barriers', but I presume that's not enough for what you're talking about?

Kind Regards, John.

 

[ban-all-sheds]

Never seen that requirement in the 17th. Or 16th.

The only thing I would say is that if you're using a multi-gang switch which is an all-in-one lump behind the faceplate, one more than one phase, pay attention to what voltage it is rated for....

 

[JohnW2]

The only thing I would say is that if you're using a multi-gang switch which is an all-in-one lump behind the faceplate, one more than one phase, pay attention to what voltage it is rated for....

Yes, that's likely to be the crunch. I can't recall ever having seen any plate switch, single- or multi-gang, which had anything other than "250V" embossed on it. I have to say that, intuitively, I don't think it would even occur to me to have more than one phase going to such a switch, whatever it had written on it!

Kind Regards, John.

 

[radweld]

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.

Perhaps - but I seem to recall countless discussions of potential confusion prior to harmonisation which presumably lead to the assumption that a warning was necessary.

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.

Surely that's because 'best practice' improves over time. And also is this the first time a phase colour becomes neutral and vice versa between two versions of the regs?

The layman, or at least the person who knows no basic chemistry, will understand far more from a warning which says "Danger - Acid.

Agreed. But in this case it's like placing a warning label saying 'pH 0.5' on some acids, but not labelling acid with a pH of 1.0.

I can't think of anything additional a user should do when seeing a 400V warning. It's actually not much use as a warning to a casual tinkerer as the real risk comes from the fact it's polyphase wiring rather than the voltage per se - this is far from obvious just from a 400V voltage.

It would be much more useful to put a sticker on the distribution board saying the installation contained multiple phases and voltages over 230V. Although such a sticker may cause embarrassment, apparently

 

[JohnW2]

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.

Perhaps - but I seem to recall countless discussions of potential confusion prior to harmonisation which presumably lead to the assumption that a warning was necessary.

Fair enough - but, as I said, if in 2011 someone contemplating doing work on an electrical installation needed to be told about the 'two colours' situation, I would be very seriously concered about what else they needed to be told (by labels) before they could safely do the work.

It would be much more useful to put a sticker on the distribution board saying the installation contained multiple phases and voltages over 230V. Although such a sticker may cause embarrassment, apparently

Hmmm. I would not be in the slightest embarrassed by a sticker which was informative about the installation; indeed, I have labelling such as you mention on my CUs. The embarrassment I referred to related to what any 'electrician' who had done at least one day's 'training' should feel if (s)he was being told by a label about cable colours, and the need to carefully identify conductors.

Kind Regards, John.

 

[Paul_C]

Never seen that requirement in the 17th. Or 16th.

I had a feeling it been removed some time ago. I no longer have a copy of the 15th edition in which to check, so it may have even been removed then.

The only thing I would say is that if you're using a multi-gang switch which is an all-in-one lump behind the faceplate, one more than one phase, pay attention to what voltage it is rated for....

And related to that and the original topic of this thread, that's an issue with switchgear used on single-phase 3-wire systems. Most of the "normal" domestic apparatus is now only 400/415V, so not rated by the manufacturer as being suitable for use on the 460/480V found between poles where a home is fed with a single-phase 3-wire supply. It starts getting rather more expensive going to switchgear rated for 500V or more.

Surely that's because 'best practice' improves over time.

Changes over time are not always improvements though, in terms of making things stricter or more cautious. The above comments about warning notices relating to the maximum voltage present illustrate that: For 415V or 480V supplies we've gone from a warning notice always being required, to a warning being required only if those voltages would not normally be expected, to no warning being required at all.

And also is this the first time a phase colour becomes neutral and vice versa between two versions of the regs?

The first time there has been a mutual swapping of places as with blue & black perhaps, but not the first time a color has changed to "the other side." The change to European flex colors circa 1970 resulted blue in old flexes being a phase and blue in new flexes being neutral. And it resulted in a situation where for the next 40 years newly installed flexes were using blue for neutral but newly installed fixed cables still used it as a phase.

 

[radweld]

Surely that's because 'best practice' improves over time.

Changes over time are not always improvements though, in terms of making things stricter or more cautious. The above comments about warning notices relating to the maximum voltage present illustrate that: For 415V or 480V supplies we've gone from a warning notice always being required, to a warning being required only if those voltages would not normally be expected, to no warning being required at all.

I would argue that at worst this relaxation has a neutral impact on safety. As I mentioned, I am not sure what a '400/415V' warning actually contributes to safety. Most warning labels tend to be in place more to avoid litigation rather than as a pragmatic contributor to safety. Removing superfluous warnings is rather important in order to maximise real safety. Unfortunately, practical safety is usually overridden by the need to CYA.

 

[Paul_C]

Well, whatever result that particular change may have had, it was just one example which came to mind immediately as we'd been discussing it. The point to be made is that many people assume that each new edition of the regs. imposes stricter requirements, and that's simply not always true. Other examples which come to mind quickly are the relaxation of the rules requiring isolating switches for appliances, increased current ratings for cables, and removal of the requirements for supplementary bonding.

 

[JohnW2]

The point to be made is that many people assume that each new edition of the regs. imposes stricter requirements, and that's simply not always true.

I agree with that.

However, I think we have to assume that no 'relaxation' (i.e. reduction in 'strictness') is ever introduced which, in the minds of those writing the regs, results in a reduction in the level of safety. You may disagree with their judgement in some cases, but I think we have to assume that such is what they believe.

Kind Regards, John.