Electrical Codes, Standards, Conductors, and Insulators
Chapter 3: Codes and Standards
The design of electrical installations is done within a legal framework. An engineering project is a technically and economically appropriate response, which complies with the standards and codes.
In Mexico, NTIE (Technical Standards for Electrical Installations) issued by the Directorate General of Standards, constitute the legal framework mentioned above.
Other standards that are not mandatory can support areas not covered by the NTIE:
- a) The NEC (National Electrical Code U.S.) can be very useful in some applications.
- b) The LPC Code (protection against electric shock U.S.) is a chapter of the NFPA. Mexican projects rely heavily on this code because the NTIE treats it with little depth.
Chapter 4: Electric Conductors and Insulators
This concept applies to bodies capable of conducting or transmitting electricity.
An electrical conductor is formed primarily by the driver itself, usually copper.
This can be a wire, i.e., a single strand, or a cable consisting of multiple threads or wires twisted together.
The materials used in the manufacture of electrical conductors are copper and aluminum.
Although both metals have excellent electrical conductivity, copper is the main component in the manufacture of drivers for their remarkable mechanical and electrical advantages.
The use of either material as a conductor will depend on their electrical characteristics (ability to carry electricity), mechanical properties (wear resistance, malleability), the specific use, and the cost.
These features make copper preferable in the production of electrical conductors.
The type of copper used in the manufacture is electrolytic copper wires with high purity, 99.99%.
Depending on the use that is going to be given, this type of copper is presented in the following degrees of hardness or temper: hard, semi-hard, and soft or annealed.
Types of Copper for Electrical Conductors
Hard Temper Copper
- Conductivity of 97% compared to pure copper.
- For this reason, it is used in the manufacture of bare conductors for overhead electricity transmission, which requires good mechanical strength.
Soft Copper or Soft Temper
- 100% conductivity
- As it is flexible and ductile, it is used in the manufacture of insulated conductors.
The driver is identified in terms of its size and caliber, which can be expressed in mm2 (millimeter) or in AWG or MCM (American), with an equivalent in mm2.
Component Parts of Electrical Conductors
These are three very different parts:
- The core or conductive element.
- Insulation.
- Protective covers.
The Core or Conductive Element
It is manufactured in copper and its goal is to provide a way for electric power from generating plants to distribution centers (substations, networks, and connections), to feed the different consumption centers (industrial, residential groups, etc.).
The way the core is organized determines the classification of electrical conductors. So we have:
According to its Constitution
Wire: Conductor whose electrical conducting core comprises a single element or wire.
Used by airlines, such as bare or insulated conductors, electrical installations outdoors, in ducts, or directly on insulators.
Cable: Electrical conductor whose core driver consists of a series of wires or wires of a small section, which gives it great flexibility.
According to the Number of Drivers
Single core: Electrical conductor with a single conductive core, insulated and with or without protective covering.
Multiconductor: Conductor with two or more insulated conductive cores together, each wrapped in their own layer of insulation and one or more common protective covers.
Insulation
The purpose of the insulation on a conductor is to prevent the electricity flowing through it from contacting people or objects, whether these are products, appliances, or other items that are part of an installation. Similarly, the insulation must prevent different voltage drivers from making contact.
The insulating materials used from the beginning have been polymeric substances, which are defined as a chemical material or chemical body formed by the joining of many identical molecules to form a new, thick molecule.
Formerly, the isolates were of natural origin, gutta-percha, and paper. Technology subsequently exchanged them for current artificial insulation commonly used in the manufacture of electrical conductors.
Different types of insulation for the conductors are given by technical and mechanical behavior, considering the environment and conditions of the pipeline that the drivers will be subjected to that they protect, resistance to chemicals, sunlight, humidity, high temperatures, flames, etc. The materials used for insulation of wires include PVC or polyvinyl chloride, polyethylene (PE), rubber, neoprene, and nylon.
If the design of the driver does not include other protection, it is called integral insulation because the insulation does its job and the coating at the same time.
When drivers have other protection on the insulating polymer, the latter is called a casing, jacket, or cover.
Protective Covers
The main objective of this part of a conductor is to protect the integrity of the insulation and conductive core against mechanical damage such as scrapes, bruises, etc.
If mechanical protections are steel, brass, or another durable material, this is called “armor.” The “framework” can be tape, wire, or stranded wires.
Drivers can also be equipped with electrical protection type films formed by aluminum or copper. When that protection, rather than tape, is made up of copper wires, it is called a “screen” or “shield.”
Conductive Core – Insulating – Protective Cover
Classification of Electrical Conductors
According to Their Isolation or Number of Threads
The most important part of a power system consists of the drivers.
In designing a system, either of power or control of information, certain parameters are necessary for the specification of the wiring.
- System voltage, type (DC or AC), phase and neutral power system, central grounding point.
- Current or power supply.
- Operating temperature, ambient temperature, and thermal resistivity around.
- Type of installation, dimensions (depth, radii, distance between openings, etc.).
- Overloads or intermittent loads.
- Type of insulation.
- Protective cover.
All these parameters are closely related to the type of insulation and type of construction of electrical conductors and must be decided according to this background, the type of use which will be given.
According to them, drivers can be classified according to their electrical insulation, building, and number of strands in single-core and multi-core.
Taking into account its type, use, environment, and consumption, electrical conductors are classified as follows:
Drivers for Distribution and Power:
Application: power and lighting installations (air, groundwater, and indoor).
Armored Cables:
Use: Plant in underground mine shafts and galleries (ducts, trays, overhead, and underground)
Armored
Cords:
Application: For light duty, power to: radios, lamps, vacuums, juicers, etc. Powered industrial machinery and electrical equipment, appliances, and heating appliances (washing machines, polishers, refrigerators, stoves, grills, stoves, and ovens, etc.).
Portable Cables:
Use: electric welding machines, locomotives, and traction engines in underground mines. Cranes, shovels, and drills for mining use. Resistant to weather, chemicals, flame, and high mechanical loads and hauls, cuts, and impacts.
Submarine Cable:
Use: in areas under water or completely submerged, with mechanical protection which makes them resistant to current and seabed.
Marine Cables:
Use: designed to be installed on ships in circuits of power distribution and lighting.
Within the range of wires and cables that are manufactured in the country, there are other types, for industrial uses, such as telephone wires, magnetic wires enamel for use in the electronics industry and the winding of items and traction motors, cables for connection to automotive batteries and starter motors, cables for speakers, and wire rings.
According to Their Conditions of Employment
For high-power lines and low voltage, in our country, there are various types of copper conductors, bare and insulated, designed to respond to various driving needs and characteristics of the environment in which the facility will serve.
The selection of a driver will make sure considering that a sufficient current carrying capacity, an adequate ability to withstand short circuit currents, adequate strength, and appropriate behavior to environmental conditions it will operate.
Bare Copper Conductors
These are wires or cables and are used for:
- Urban and suburban airline networks.
- High-voltage overhead lines outdoors.
- Overhead contact lines for railways and trolley-buses.
Wire and Insulated Copper Cables
These are used in:
- Overhead distribution lines and power connections, etc.
- Indoor facilities motive power and lighting, located in different natural environments and with different types of pipe.
- Overhead lines in mining (blasting, cranes, drills, etc.).
- Lying directly in the ground, trays, or ducts.
- Underground mine shafts and galleries.
- Command and control circuitry (substations, industrial, etc.).
- Power lines in parts of furnaces and high temperatures.
- Power lines underwater (submarine cable) and ships (naval drivers).
- Other conditions that require security.
Unable to insert in this booklet all the tables that exist with the specifications and conditions of use of copper wire, both bare and insulated, delivered by way of example some of the most used by professionals technicians and specialists. It is recommended to ask the producers and manufacturers specifications to obtain the information needed for electrical projects.