Although I find it hard to believe that BAS is not being deliberately obtuse, here is a short excerpt from the rules which cover the wording of BS7671.
View attachment 151419
I am not being obtuse, either by accident or design. I genuinely was unaware of the rules which you showed.
In my defence, I will point out that so are the authors of BS7671. There are 705 instances of the word "
may" in the online final draft version of the document, including, to be fair, at least one where they are talking about the month of May, and some where they are showing the old wording struck out. Interestingly an awful lot of them work just as well read as "
might" or "
is permitted", and with many it is obvious from the context that permission rather than possibility is what is meant.
But not all. I'll pick a few choice ones, rephrase them in the light of that rule, and we'll see how they read.
- In electrical installations, risk of injury is permitted to result from:
(i) shock currents
(ii) excessive temperatures likely to cause burns, fires and other injurious effects
.
.
- Effective means, suitably placed for ready operation, shall be provided so that all voltage is permitted to be
cut off from every installation, from every circuit thereof and from all equipment, as is permitted to be necessary to prevent or
remove danger.
- If the distributor changes the characteristics of the power supply this is permitted to affect the safety of the installation.
- Cable channel. ... A cable channel is permitted to or is not permitted to form part of the building construction.
- Cable tray. ... A cable tray is permitted to or is not permitted to be perforated.
- Emergency switching. An operation intended to remove, as quickly as possible, danger, which was permitted to have occurred unexpectedly.
- Fault. A circuit condition in which current flows through an abnormal or unintended path. This is permitted to result from an insulation failure or a bridging of insulation
- Non-compliance. A non-conformity that is permitted to give rise to danger.
- Temporary overvoltages are permitted to be caused by faults inside the LV system (UTOV,LV) or inside the HV system (UTOV,HV)
- The supply system PEN conductor is earthed at two or more points and an earth electrode is permitted to be necessary at or near a consumer’s installation.
- Every installation shall be divided into circuits, as necessary, to:
.
(iii) take account of hazards that are permitted to arise from the failure of a single circuit such as a lighting circuit
- The resistance of the installation earth electrode should be as low as practicable. A value exceeding 200 ohms is permitted to not be stable. Refer to Regulation 542.2.4.
- To reduce overvoltage or to damp voltage oscillation, it is permitted to be necessary to provide earthing through impedances or artificial neutral points,
- The factor 2 in both formulae takes into account that in the event of the simultaneous occurrence of two faults, the faults are permitted to exist in different circuits.
- Therefore this protective measure shall not be applied to any circuit that includes, for example, a socket-outlet with an earthing contact, luminaire supporting coupler (LSC), device for connecting a luminaire (DCL) or cable coupler, or where a user is permitted to change items of equipment without authorization. [comment]I love that one. A user being permitted to change something without permission. Brilliant.[/comment]
- If, behind a barrier or in an enclosure, an item of equipment such as a capacitor is installed which is permitted to retain a dangerous electrical charge after it has been switched off, a warning label shall be provided.
- Attention is drawn to the risk that, where electrical installations are not under effective supervision, further conductive parts are permitted to be introduced at a later date (e.g. mobile Class I equipment, or extraneous-conductive-parts such as metallic water pipes), which are permitted to invalidate compliance with Regulation 418.1.6. [comment]That seems a very strange thing to permit, IMO.[/comment]
- Electrical separation of an individual circuit is intended to prevent shock currents through contact with exposed-conductive-parts that are permitted to be energized by a fault in the basic insulation of the circuit.
- Persons, livestock and property shall be protected against harmful effects of heat or fire which are permitted to be generated or propagated in electrical installations.
- Harmful effects of heat or fire are permitted to be caused by:....
- Where a resistive fault is permitted to cause a fire, e.g. for overhead heating with heating film elements,..
- An overcurrent is permitted to be an overload current or a fault current.
- If disconnection of a single line conductor is permitted to cause danger, for example in the case of a three-phase motor, appropriate precautions shall be taken.
- Overcurrent detection shall be provided for the neutral conductor in a polyphase circuit where the harmonic content of the line currents is such that the current in the neutral conductor is permitted to exceed the current-carrying capacity of that conductor. The overcurrent detection shall cause disconnection of the line conductors but not necessarily the neutral conductor.[comment]So you have to detect and stop something which is allowed to happen?[/comment]
- A reduction in current-carrying capacity is permitted to be due to a change in cross-sectional area, method of installation, type of cable or conductor, or in environmental conditions.[comment]Jolly decent of JPEL/64 to permit the laws of physics to apply, if you ask me.[/comment]
- Where current-using equipment or any other part of the installation is permitted to be damaged by a drop in voltage....
- Where reverse-current braking of a motor is provided, provision shall be made for the avoidance of reversal of the direction of rotation at the end of braking if such reversal is permitted to cause danger.
- A protective device shall be arranged and identified so that the circuit protected is permitted to be easily recognized.
- Heat from external sources is permitted to be radiated, conducted or convected, e.g.:.. [comment]Again, nice to see that they are allowing the laws of physics to apply.[/comment]
- For mineral insulated cables, higher operating temperatures are permitted to be permissible... [comment]Hmm...[/comment]
- It shall be of adequate mechanical stability to withstand the stresses which are permitted to arise through damage to the support of the wiring system due to fire.
CBA to post any more. Judging by where the slider is in my search results pane I reckon I've gone about ⅓ of the way through the list, so there are plenty more opportunities for people to find daft examples if anybody wants to.
But basically, Detlef, no matter what the rules may say, it is demonstrably obvious that there are dozens and dozens of instances in BS7671 where "may" does
not mean permission, but does mean possibility.
To accuse me of being obtuse because (a) I was as unaware of the rule as the authors appear to be, and (b) I did not think it possible that what they meant was "
Wiring systems hanging across access or egress routes are permitted to hinder evacuation and firefighting activities", and that therefore there was an ambiguity which should be removed is not really on.
IMO, anybody who cannot tell from the context whether "
may be" means "
might be" or "
is permitted to be"
when it matters probably has no business trying to do electrical work.
