17th Edition Part 4 4
- 1. Requirements for Electrical Installations IEE Wiring Regulations 17 th Edition Part 4 Chapter 44
- 2. IEE Wiring Regulations 17 th Edition - Part 4 As previously stated: It consists of only 4 chapters, 41 – Protection against Electric Shock . 42 – Protection against Thermal Effects . 43 – Protection against Overcurrent. Last one Tonight: - 44 – Protection against voltage disturbances and Electromagnetic Disturbances .
- 3. Requirements for Electrical Installations IEE Wiring Regulations 17 th Edition Part 4 Chapter 44
- 4. Chapter 44 Protection against Overcurrent There are 6 sections in this chapter 440 – Introduction 441 – Not used 442 – Protection of low voltage installations against temporary overvoltages due to various faults 443 – Protection of overvoltages of atmospheric origin or due to switching 444 – Reserved for Measures against electromagnetic Influences 445 – Protection against undervoltages
- 5. Chapter 442 Protection of low voltage installations against temporary overvoltages due to earth faults in the high voltage system due to faults in the low voltage system The following four situations can have an effect on the safety of an LV installation by creating temporary overvoltages: A fault between the HV system and Earth in the transformer. (Regulation Group 442.2) Loss of the supply neutral in the LV installation (Regulation 442.3)
- 6. Chapter 442 Protection of low voltage installations against temporary overvoltages due to earth faults in the high voltage system due to faults in the low voltage system Accidental earthing of a line conductor of an LV IT system. (Regulation 442.4) Short-circuit between a line conductor and neutral in the LV installation. (Regulation 442).
- 7. 443 – Protection against overvoltages of atmospheric origin or due to switching As the UK has ≤ 25 thunderstorm days per year (AQ1), NO additional protection is required against overvoltages of atmospheric origin where installations are supplied by LV overhead lines, provided …
- 8. Required minimum impulse withstand voltage Refer to Table 44.4 for examples of various impulse categories of equipment Nominal voltage of the installation V Required minimum impulse withstand voltage kV Category IV (equipment with very high impulse voltage) Category III (equipment with high impulse voltage) Category II (equipment with normal impulse voltage) Category I (equipment with reduced impulse voltage) 230/240 or 277/480 6 4 2.5 1.5 400/690 8 6 4 2.5 1000 Values to be determined by the system engineer or, in the absence of information, the values for 400/690 V can be chosen.
- 9. 443 – Protection against overvoltages of atmospheric origin or due to switching Switching overvoltages may be generated within an installation as the result of switching of: high current loads, inductive loads, such as motors, transformers or arc welding equipment, or capacitive loads, such as power factor correction equipment.
- 10. 444 – Measures against electromagnetic influences Reserved for future use
- 11. 445 – Protection against undervoltage
- 12. 445 – Protection against undervoltage As in 131.1 (v) we are going to protect persons and livestock against Mechanical movement from electrically actuated equipment . . . . .
- 13. 445 – Protection against undervoltage This also includes:- Suitable time delay being incorporated in the operation of an undervoltage protection device. Any time delay not reactivate a contactor and not impede the disconnection of a control or protective device. That such a device shall be compatible with the requirements for starting as stated in the appropriate British Standard. Where the automatic reclosure of a device may cause danger
- 14. 445 – Protection against undervoltage The most used equipment falling into this category is:- Incorporated into motor starters . . . . i.e. The “No Volt Coil” in the contactor.
- 15. Chapter 44 Protection against Overcurrent Does this make sense? GOOD – We will carry on - - - - - - - - To Part 5 - - - - - - Next Session
Editor's Notes
- #6: Section 442 includes some difficult concepts for many students and covers requirements/situations many students are unlikely to get involved with. Section 442 gives rules for the designer and installer of the substation. It is suggested, therefore, that the best approach to this subject matter is to provide an overview of the general requirements It would be wise to mention that the requirements of Regulations 442.2.1 and 442.2.2 are deemed to be fulfilled for installations receiving a supply at low voltage from a system for distribution of electricity to the public In addition, refer to Regulation 442.2.3 for the need NOT to perform the calculation U 1 , U 2 and U f (see Fig 44.1) as it mainly falls into the responsibility of the substation installer/owner/operator to fulfil requirement provided by IEC 61936-1.
- #8: This section deals with protection of electrical installations against transient overvoltages of atmospheric origin transmitted by the supply distribution system and against switching overvoltages generated by the equipment within the installation. The term ‘overvoltages of atmospheric origin’ relates to lightning, although direct lightning strikes on the LV lines of supply network or on electrical installations are not taken into account . Often, overvoltages of atmospheric origin are induced into overhead lines by nearby lighting strikes or the close proximity and movement of charged clouds . Two levels of protection against overvoltage are identified in Section 443: Equipment should have an adequate impulse withstand voltage for its intended use, or surge protection devices are used, which is not required in the majority of installations in the United Kingdom.
- #9: The rated impulse withstand voltage of an item of equipment is the peak value of an impulse voltage of prescribed form and polarity that the equipment can withstand under specified test conditions without failure. Surge protection devices is an alternative to the AQ criteria. (443.2.4 refers.)
- #11: This is an empty Section at the moment. Information may be added when Amendment No. 1 is issued.
- #12: Suitable precautions need to be taken where a reduction or loss in voltage may occur to such a level so as to cause failure of equipment, or in some cases damage depending on the nature of the equipment connected. For example, a three-phase motor may be damaged by the motor drawing current from only two phases. Where unexpected restarting of a motor might cause danger it should be fitted with means to prevent automatic restarting after a stoppage due to a drop in voltage or failure of supply