Low Voltage Electrical Installations in Buildings: Design & Regulations
Low Voltage Electrical Installations in Buildings
Regulations and Design Considerations
The fundamental regulation for the calculation and design of low voltage installations is the Low Voltage Electrotechnical Regulations (REBT) and its Complementary Technical Instructions (ITC), as per Decree 842/2002 of August 2nd. However, it’s crucial to consult the specific regulations of different suppliers.
Electricity Distribution in Buildings
Electricity distribution in buildings typically operates at low voltage, defined as less than 1000 volts. Common voltages used within this range include:
- 230 V between phase and neutral
- 400 V between phases
Reserve for Local Processing Center
Electricity distribution in cities often utilizes both low and medium voltage. When medium voltage is used, transformers are necessary to reduce it to low voltage. These transformers should be accessible directly from the street. If this isn’t feasible, access corridors must have a minimum width of 1.50 meters and a height of at least 2.80 meters.
Load Forecasting in Housing Construction
Determining the expected power consumption (kW) of a building involves calculating estimates for various components and summing them. This process includes:
Load Forecasting for Each Dwelling
Each dwelling is assigned a degree of electrification, typically the basic electrification level.
Load Forecasting for the Whole Housing
For lines supplying multiple dwellings, a reduction in computing power is permitted compared to the sum of individual households.
Load Forecast for General Service Building
The computing power is the sum of all general service computers without applying a simultaneity coefficient.
Review of Charges for Commercial Premises and Offices
A minimum of 100 W/m2 is considered, with a local minimum of 3,450 VA at 230 V.
Anticipating Charges of Garages
A minimum of 10 W/m2 is required for garages with natural ventilation and 20 W/m2 for those with forced ventilation, with a local minimum of 3,450 VA at 230 V.
The Mains
This component of the public distribution network feeds the general protection box(es) (CGP) or equivalent unit. It usually serves a building complex, although special supplies may cater to more than one.
Installation of the Link
The link installation connects the external supply network to the building’s internal installation. Key components include:
- General Protection Fund (CGP)
- Power Line
- Elements of the location counter
- Individual Referral
- Housing for power switch
- Control and protection devices
General Protection Fund (CGP)
This typically protects the electrical system within the building, marking the boundary between the utility company’s and the building’s installations. It houses elements that protect the general power line.
Location and Installation
Its location is determined by agreement between the distributor and the property owner, usually at the front of the property or in easily accessible common areas. It should be close to the urban distribution network or processing center and separated from water, gas, and telephone facilities.
Aerial Connection
For aerial connections, the CGP can be surface-mounted at a height of 3 to 4 meters above ground.
Underground Connection
Underground connections require installation in a wall niche, preferably enclosed with a metal door (IK 10 protection according to UNE-EN 50 102) and a lock or padlock. The door bottom should be at least 30 cm above the ground.
Constitution
CGP housings are typically made of flame-retardant fiberglass-reinforced polyester. They contain short-circuit fuses for each phase and a neutral connecting terminal.
Designation
CGPs are designated with the abbreviation “CP” followed by a number and the letters E, I, or U.
General Protective Boxes According to Amperage
Boxes are available in various amperage ratings, including 40 A, 80 A, 100 A, 160 A, 250 A, and 400 A.
Types of Wiring Diagrams
Six different connection schemes are possible within the CGP, accommodating various building configurations and entry/exit points for the general power line.
Getting Connected
To ensure safety, connect the general power line to the CGP first, followed by the connection to the distribution network.
General Line of Food (LGA)
This line connects the Protection Fund to the meter centralization point. It should be as short and straight as possible. In some houses, this line might not exist, with the CGP connecting directly to the subscriber meter.
Placement in Vertical Pipe
Vertical power lines typically run within a dedicated pipe or masonry shaft, often attached to the stairwell. This shaft should be at least 30 x 30 cm and exclusively for the power line. It should be sealed at each floor and have fire-resistant walls.
Placement on Inner Tubes
Inner tubes should have a nominal diameter that allows for 100% expansion of the installed conductors.
Counters (Meters)
These devices measure individual electricity consumption. They can be placed individually or in a concentrated manner.
Individual Placement
Used for single-user supplies or two independently fed users from the same location.
Placement in a Concentrated Form
Suitable for residential buildings, commercial premises, commercial buildings, and industrial concentrations. Meters can be concentrated in one or more locations, each with a dedicated cabinet or room.
Characteristics of Local Accountants
The room for concentrated meters should be dedicated exclusively to this purpose, easily accessible, and well-ventilated. It should comply with fire safety regulations and be separated from other service areas.
Features of Meter Cabinet
Meter cabinets should be located on the ground floor, mezzanine, or first basement. They should be fire-resistant, well-ventilated, and have a lock. A grounded 16 A socket should be provided for maintenance.
The Concentration Meter
The meter concentration should be installed at a height that allows for easy reading. It typically consists of several functional units, including a general operating switch, safety fuses, measurement unit, control unit, protection and output terminal unit, and optionally, a telecommunications unit.
Individual Tap (DI)
These lines connect the meter(s) to the private control and protection devices. They should be placed in common areas whenever possible.
Placement in Vertical Pipe
Similar to the power line, vertical individual taps are housed in dedicated pipes or masonry shafts with fire-resistant walls. These shafts should be sealed and accessible for inspection.
Placement on Inner Tubes
Protective tubes and channels should allow for 100% expansion of the installed conductors. A reserve tube should be provided for future extensions.
Installation Liaison
Power Control Switch (ICP)
This automatic switch, part of the metering equipment, controls instantaneous power consumption to prevent exceeding the contracted power limit.
Overview of Control and Protection
The control and protection panel, also known as the switchboard, houses safety and distribution devices for the internal installation. It’s typically located near the house entrance and made of non-flammable materials.
Elements that Make Up the Switchboard
Key elements include an automatic cutoff switch (IGA), a high-sensitivity switch (ID), and omnipolar cutting devices for each circuit (PIAS).
Types of Switchboards
The number of elements in a switchboard depends on the level of electrification in the home.
Premises Containing Electrification a Bathtub or Shower
The REBT defines specific spaces around bathtubs and showers (Volumes 0, 1, 2, and 3) with limitations on electrical installations to ensure user safety.
Volume 0
Encompasses the interior of the bathtub or shower.
Volume 1
Extends around the bathtub or shower, including the space below, accessible without tools.
Volume 2
Surrounds Volume 1, extending up to 2.25 meters above the ground.
Volume 3
Encompasses Volume 2, extending up to 2.4 meters outward and including any space under the bathtub or shower accessible with tools.