17th Edition Part 4 4

Requirements for Electrical Installations
IEE Wiring Regulations
17 th Edition
Part 4
Chapter 44

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 .

Requirements for Electrical Installations
IEE Wiring Regulations
17 th Edition
Part 4
Chapter 44

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

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)

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).

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 …

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.

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.

444 – Measures against electromagnetic influences Reserved for future use

445 – Protection against undervoltage

As in 131.1 (v) we are going to protect persons and livestock against
Mechanical movement from electrically actuated equipment . . . . .

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

The most used equipment falling into this category is:-
Incorporated into motor starters . . . .
i.e. The “No Volt Coil” in the contactor.

Chapter 44 Protection against Overcurrent
Does this make sense?
GOOD – We will carry on - - - - - - - -
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17th Edition Part 4 4

by Paul Holden

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