Low Voltage Electrical Installations: A Comprehensive Guide
ITC.36: Facilities at Very Low Tensions
For the purposes of this instruction, three types of low voltage installations are considered: Security Extra Low Voltage (SELV), Protective Extra Low Voltage (PELV), and Low Voltage Functional (MBTF).
Safety Low Voltage
50 V AC or 75 V DC
2.1. Power
- A safety isolating transformer according to UNE-EN 60,742.
- A current source to ensure a degree of protection equivalent to that of the previous safety transformer.
- An electrochemical source (batteries).
- Other sources that are not dependent on MBTF or higher voltage circuits, e.g., generator.
2.2. Installation Conditions of the Circuits
- Physical separation of the drivers.
- The driver of the low voltage circuits SELV or PELV should be…
- The driver of the circuits to voltages must be separated by a metal shield connected to earth or a grounded metal sheath.
- A multi-conductor cable or a grouping of drivers may contain circuits to voltages, provided that drivers SELV or PELV circuits are isolated, individually or collectively, to the highest voltage endured.
Outlets of SELV and PELV Circuits
Outlets of SELV and PELV circuits must meet the following requirements:
- The connectors should not be able to enter the base outlet for other stresses.
- The bases must prevent the introduction of connectors designed for other voltage-socket bases. SELV circuits should not wear contact protection, PELV circuits can take it.
- The connectors of SELV circuits should not be able to enter the PELV power sockets.
- The connectors PELV circuits should not be able to enter the SELV socket outlets.
Cable Installation
The buried cable will be placed between two layers of fine soil or sand screened, 10 to 15 inches thick.
When the wires do not exhibit sufficient mechanical strength, they are placed inside ducts to protect them properly.
Voltage Drop
For installations for lighting, the voltage drop between the power source and point of use shall not exceed 5%.
Protection Against Direct Contact
When the rated voltage of the circuit is greater than 25V AC or 60V DC without undulation, ensure protection against direct contact with one of the following methods:
- Barriers or enclosures presenting at least a degree of protection IP2X, or IP XXB according to UNE 20,324.
- Insulation that can withstand a voltage of 500 volts for one minute.
The current ripple is not one in which the percentage of ripple does not exceed 10% of RMS.
The protection against direct contact must be ensured:
- On the barriers or enclosures who have at least a degree of protection IP2X, or IP XXB.
- For insulation that can withstand a voltage of 500 volts for one minute.
However, it requires protection against direct contact:
- Effective 25V AC or 60V DC without undulation, as long as the equipment is used only in dry locations and do not provide contacts between Swiss and body active parts human or an animal.
- Effective 6V or 15V alternating current into direct current without ripple.
ITC-35: Facilities for Special Purposes – Horticultural Farms
This instruction applies to fixed installations of agricultural and horticultural whom are animals (such as stables, barns, poultry houses, piggeries, premises for the preparation of animal feed, barns, farms for hay, straw and fertilizers) or are situated outside the premises habitable be excluded.
ITC 37: Facilities at Special Tensions
Facilities for special voltages are those in which the nominal voltage is greater than 500V RMS or 750V alternating current of arithmetic mean current, within the scope of these rules.
These facilities, besides meeting the requirements established for the common voltage installations and additional requirements according to their location, perform the following:
- It necessarily applies one system of protection for indirect contact indicated in the ITC-BT-24, both the conductive wrap pipes as the masses of the devices which have no double insulation or reinforced insulation.
- The cables used are always rated voltage not exceeding 1,000 V. When these cables are installed on insulating supports, they should have an envelope that protects against mechanical damage.
- The presence of bare energized parts that are not fully protected against direct contact, according to the provisions of instruction ITC-BT-24, is allowed only in places pertaining to electric service, provided that only qualified personnel have access to it.
- The wiring shall be easily identifiable, especially when there are other pipelines in the vicinity of a common voltage or small tensions.
- The usual voltage installation, from their protective devices shall be isolated as the installation of special stress on the exceptional case of use of a compensator for the usual rise in blood to the particular stress.