Continuing our look at the changes in the Rules we now turn our attention to Chapter 44 Protection against voltage disturbances and electro magnetic disturbances: Firstly you might notice that the name of the chapter has been altered from the shorter “protection against over-voltages” to the more precise “Protection against voltage disturbances and electro magnetic disturbances”.
The content of the chapter has changed dramatically. Many of the changes seen here first appeared in the second amendment to ET101which was issued in September 2005. The main changes can be found in 443 “Protection against over-voltages of atmospheric origin or due to switching”. The Wiring Rules committee agreed that over-voltages due to atmospheric origin i.e. lightning or as it is described in the Rules “Keraunic Activity” was not as prevalent in Ireland as on mainland Europe. The proof that this is so can best be illustrated when using the IEC risk assessment calculations found in IS EN 62305-2. The results tend to point to a conclusion that protection is not mandatory. Obviously this is due to the low level of Keraunic activity in Ireland which tends to skew the calculations. However other factors should come into consideration which often over-rules the initial outcome of the risk assessment based on the probability of a lightning strike. Factors such as loss of human life, loss of service to the public, loss of cultural heritage, loss of economic value (e.g. structure, content, commercial activity). When factors such as these are considered the result nearly always is that lightning protection is installed. In fact there is one sentence in IS EN 62305-2 which illustrates this point effectively: “The decision to provide lightning protection may be taken regardless of the outcome of any risk assessment where there is a desire that there be no avoidable risk”.
In the introduction to 443 the effects of switching surges are given more prominence than in comparable documents. This is because the Wiring Rules Committee felt the need to raise the awareness levels that this particular phenomenon is more of a problem in modern day electrical installations than its more powerful atmospheric rival. Interestingly an industry accepted fact that eighty per cent of switching surges originate within the affected electrical installation was considered important enough to mention in the introductory text. The purpose behind including this fact was to focus the reader’s attention on the importance of whether or not the electrical contractor should consider fitting local surge protection devices.
Moving on to Chapter 46: Isolation and switching we find that most of the original content has been transferred to Chapter 53 and in particular to section 537. Only the basic Rules have been retained here such as:
462 Isolation
463 Switching-off for Mechanical maintenance,
464 Emergency Switching and Emergency Stopping
465 Functional switching and control
Chapter 48: Choice of Protective Measures as a Function of External Influences has been removed from the fourth edition of ET101, and its content has been redistributed to various chapters e.g. Chapter 42, 729
Within Part 5 there are a number of important changes which affect the selection and erection of electrical equipment.
Chapter 51: Common Rules and external influences.
Section 514 Identification and marking contains the internationally agreed colour code for cables. It is vital to remember that the Irish Wiring Rules contain some important Special National Conditions (SNC’s) with regard to core colours. The colour blue can only be used for neutral. Sleeving is not permitted under any circumstances up to and including 120 sq mm. Conductors with an insulation colour Green/ Yellow can only be used for the purpose of earthing and bonding. They may not be screened under any circumstances. Another rule to watch out for is the requirement that all line/phase conductors shall be identified throughout their length by the colours brown, black or grey. In multi-phase installations, line/phase conductors shall be distinguished from one another by the colours brown, black, and grey corresponding to the respective phases in accordance with Table 51A as shown in the Rules. Therefore you cannot use one colour for a three phase circuit except where the conductor size has a maximum cross sectional area exceeding 120 sq mm. The intent behind this requirement is to alert the electrical contractor to the fact that there is 400V present and additional precautions may need to be taken.
Where PEN conductors are installed in Ireland it is preferred that a blue conductor is used and fitted with green and yellow markings at the terminations. The logic behind this rule is that the blue colour will alert someone to the fact that the conductor concerned could be carrying a current!
In next months issue we will continue our look at the changes in the new Wiring Rules and the reasons behind the changes.