CHAPTER 51
Chapter 51 focused on the selection and erection of electrical equipment. This chapter would have provided guidance and standards for the appropriate selection, installation, and arrangement of various electrical equipment and components used in electrical installations. It provides common rules for compliance with, measures of protection for safety requirements, for proper functioning for intended use of the installation Requirements appropriate to the external influence.
General Requirements
Compliance with Standards
Equipment Standards
All equipment must comply with the relevant British or
Harmonized Standard applicable to its intended use. The edition used should be
the current one with applicable amendments. If equipment complies with a
foreign national standard based on an IEC Standard, the designer must verify
that it offers safety levels equivalent to the British Standard.
Non-Standard Equipment
Equipment not covered by a British or Harmonized Standard,
or used outside its standard scope, must provide the same degree of safety as
compliance with the regulations.
Operational Conditions and External Influences
Operational Conditions
Voltage
Equipment must be suitable for the nominal voltage of the
installation, accounting for the highest and lowest expected voltages. In IT
systems, equipment must be insulated for the nominal voltage between lines.
Current
Equipment should handle the design current, including
capacitive and inductive effects, and any abnormal currents for periods defined
by the protective devices. Switchgear, protective devices, and accessories
should not be connected to conductors operating above 70°C unless specified by
the manufacturer.
Frequency
If frequency affects equipment characteristics, the
equipment's rated frequency must match the nominal frequency of the circuit
supply.
Power
Equipment should be selected based on power characteristics
suitable for the demanded duty.
Compatibility
Equipment must not cause harmful effects to other equipment
or impair the supply during normal service, including switching operations.
Impulse Withstand Voltage
Equipment must have an impulse withstand voltage at least
equal to the minimum required at the installation point, as defined in Section
443.
External influences
Equipment shall be of a design appropriate to the situation
in which it is to be used or its mode of Installation shall take account of the
conditions likely to been countered.
Accessibility
Every item of equipment shall be arranged so as to facilitate
its operation, inspection and maintenance and access to each connection.
Identification and notice
A label or other suitable means of identification Shall be
provided to indicate the purpose of each item of switchgear and control gear.
Here there is identification of conductors by colour or numbers and conduits.
Prevention of mutual detrimental influence.
Electrical equipment shall be selected and erected so as to
avoid harmful influence between the electrical installation and any non- electrical
installation envisaged.
Electromagnetic compatibility
The immunity levels of equipment shall be chosen taking into
account the electromagnetic influences that can occur when connected and
erected for normal use, BS NE 50082. Equipment shall be chosen with
sufficiently low emission levels so that it cannot cause unacceptable
electromagnetic interference with other electrical equipment by electrical
conduction or propagation in air (BS 50081).
CHAPTER 52
Chapter 52 outlines the regulations for selecting and
erecting wiring systems, ensuring that they are appropriate for the intended
purpose and safe under various conditions. Wiring systems must be selected and
installed according to their environmental conditions, such as temperature,
humidity, and the presence of chemicals. Considerations include the mechanical
strength of the wiring system and its ability to withstand external influences.
External influences
The selection of wiring systems must take into account
external factors like water, dust, mechanical damage, and temperature
variations. Specific wiring types and installation methods are recommended
based on the external conditions they will face.
Types of wiring systems
Various types of wiring systems include cables, bus bar
trunking systems, and flexible cords. Each type has specific standards and
regulations regarding their installation and use.
Accessibility
Wiring systems should be accessible for maintenance,
inspection, and repair. Adequate space must be provided around wiring systems
to allow for safe and effective maintenance activities.
Proximity to non-electrical Services
Electrical services should not interfere with nonelectrical
services (e.g., water, gas, steam). Proper spacing or shielding should be used
to prevent interactions that could cause harm or degrade performance.
Maintainability
Wiring systems must be designed and installed to facilitate
maintenance without compromising safety. Provisions should be made for safe
access to parts of the wiring system that may require maintenance.
CHAPTER 53
Chapter 53 establishes general requirements for protection,
isolation, switching, control, and monitoring. It covers the selection and
erection of devices to ensure safety and proper functionality of electrical
installations.
General requirements
Equipment Selection
All equipment must be selected and installed considering the
intended use and external influences to ensure safety and functionality.
Multiphase Circuits
In multiphase circuits, the moving contacts of all poles in
a multipole device must make and break simultaneously, except for the neutral
contact, which may close before and open after the others.
Neutral Conductors
Single pole switching or protective devices should not be
inserted solely in the neutral conductor in multiphase circuits.
Multifunction Devices
Devices with multiple functions must meet the requirements
for each function specified in this chapter.
Fixing of equipment
Equipment must be fixed according to the manufacturer's
instructions, ensuring connections are not subject to stress or strain.
Unenclosed equipment must be mounted in a suitable box or enclosure and
securely fixed to the building structure.
Devices for fault protection by automatic disconnection of
supply
Overcurrent Protective Devices, these include fuses, circuit
breakers, and other devices that protect against overcurrent conditions.
Residual Current Devices (RCDs) which are used to disconnect
the supply in case of earth faults.
Insulation Monitoring Devices (IMDs), these are devices used
to monitor insulation resistance in IT systems and alert users to potential
faults.
Devices for protection against fire
Devices must be installed to prevent electrical fires,
considering the installation environment and the nature of the electrical
loads.
Devices for protection against overcurrent
Overcurrent protective devices must be capable of breaking
any overcurrent occurring in the circuit.
Overload Protection devices must be selected to protect
wiring systems from excessive currents due to overloads.
Fault Current Protection devices must be capable of
disconnecting fault currents within specified time limits.
Devices for protection against under voltage
Protective devices should also address under voltage
conditions, preventing potential damage to equipment.
Coordination of protective devices
Protective devices must be coordinated to ensure proper
operation without unnecessary interruptions. Devices must be selected to ensure
that only the faulty section is disconnected, preserving the supply to the rest
of the system. Also secondary protection should be provided in case the primary
device fails.
Proper coordination between switching and protective devices
is crucial for system safety and reliability.
Isolation and Switching
Isolating devices must safely disconnect electrical circuits
for maintenance or emergencies. Specific switches must be used to isolate
equipment for safe mechanical maintenance.
Emergency switches must be easily accessible and operable to
disconnect power in hazardous situations.
Devices for functional switching must control electrical
equipment as needed.
Special switches may be required to isolate power during
firefighting operations.
Monitoring
Insulation Monitoring Devices (IMDs), these devices are used
to monitor insulation resistance in IT systems to detect faults.
Residual Current Monitors (RCMs), these devices detect and
monitor leakage currents, providing early warnings to prevent protective device
operation due to leakage.
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