BSI Standards PublicationCommunication cables Part 4-2: General considerations for the use of cables — Guide to use... NORME EUROPÉENNE English Version Communication cables - Part 4-2: G
General
When working with communication cables, an installer will deal with two basic types:
Balanced cabling involve twisted-pair and/or twinaxial twisted cables that are composed of one or more pairs of copper wires (see Figure 1)
Unbalanced cabling consists of coaxial cable, featuring a single center conductor—either solid or stranded—surrounded by an outer concentric conductor While coaxial cable is mainly utilized for CATV, satellite, and video connections, twisted-pair cabling is the predominant choice for most data and voice networks.
Figure 1 Balanced cabling Figure 2 Unbalanced cabling
Twisted pairs cables
There are two different pairing constructions:
− a pair made of two insulated wires twisted together (wire A and B in Figure 4);
− a quad made of four insulated wires twisted together, providing two pairs from a star formation (first pair wire A and B and second pair wire D and C in Figure 3);
− a pair made of two insulated wires twisted together;
− a quad made of four insulated wires twisted together, providing two pairs
Telecommunications cables vary in size, ranging from a single pair of wires to over 4,200 pairs These pairs can be organized in concentric layers or bundles Typically, a data communication terminal utilizes a maximum of four pairs, leading to the use of cables with one to four pairs for the final segment of the network In contrast, other network components aggregate multiple terminal cables, resulting in a higher number of pairs, with the main communication switch housing the largest quantity This main switch connects to global systems through various mediums, including satellite, fiber optics, radio, waveguide, and coaxial (CATV).
Each cable pair is identified using a specific color code, which is defined by relevant standards or can be mutually agreed upon by the customer and manufacturer, as illustrated in Figure 5.
Figure 5 Example of pair arrangement in a telecommunication cable
Coaxial cable (unbalanced)
Coaxial cable derives its name from its structure, which features a central conductor encased in insulation, surrounded by a concentric conductor made of metallic foil or braid, and finally enclosed in an outer sheath.
Coaxial cable is the main communication cable utilized by cable TV companies for signal distribution from community antennas (CATV, typically 75 Ω) to homes and businesses This medium has enabled access to the World Wide Web, facilitating various types of connections Historically, it served as the primary medium for Ethernet and local area networks due to its capacity to transmit high frequencies However, with the emergence of Ethernet standards over twisted-pair cables, the installation of new coaxial cables for this purpose has significantly declined.
Coaxial cables remain essential for linking CCTV cameras to monitors, antennas, and video switches Additionally, coaxial cables are utilized as feeder cables for radio communication antennas, typically operating at 50 Ω.
Triaxial (Triax) cable features a single center conductor surrounded by two shields, enhancing electromagnetic compatibility (EMC) and allowing for greater transmission distances with reduced interference In contrast, Twinaxial (Twinax) cable consists of two coaxial systems enclosed within a single concentric outer conductor and jacket, providing a compact solution for signal transmission.
Flexible cables versus rigid cables
Communication infrastructure comprises various components, including both fixed installations and those designed for dynamic environments Fixed sections, whether indoors or outdoors, feature static cables that remain in place throughout their lifespan In contrast, other sections experience continuous movement, necessitating cables that can accommodate different mechanical behaviors.
Copper is a rigid metal that contributes to the stiffness of cables, making them suitable for permanent installations Despite its rigidity, copper is highly malleable and cannot be left unsupported Therefore, cable designs incorporate features that enable appropriate bending radii, ensuring that both mechanical and transmission properties remain intact.
Flexible cables are essential for applications requiring smaller bending radii, multiple bends, or reduced stiffness while maintaining transmission properties, such as in work area cables or lift machinery To meet these needs, specific designs utilize stranded conductors instead of solid conductors, along with insulation materials that possess unique mechanical properties These cables are commonly used in cord assemblies and are rated for a specific number of mechanical cycles.
Stranded conductors are utilized in cables to enhance flexibility, making them more suitable for applications that require repeated bending, such as in robotic systems This design choice not only improves the overall flexibility of the cords but also ensures durability through numerous flexing cycles.
Cable standards determine if a cable is flexible or rigid based on its intended use throughout its life cycle Key properties to consider include simulated installation, torsion, twisting, and flexing performance tests.
To maintain optimal cable performance and prevent irreversible degradation, it is essential to adhere to fundamental principles and avoid known stresses and improper usage Various situations can adversely affect performance, causing it to fall below specified limits.
General
Cables must not only fulfill functional requirements but also comply with essential European Directives, such as the Low Voltage Directive (LVD) and the Construction Products Directive (CPD) Additionally, they may need to support system compliance with other directives, including the Electromagnetic Compatibility Directive (EMCD).
EN 50290-4-1 gives the relationship between cables and main European Directives by detailing the related cable characteristics and associated tests.
Low voltage
Cables that are described into the documents issued by CLC/TC 46X and its sub-committees are tested for voltage withstanding
The test is performed between conductors and between the conductors or screen and the outer surface of the sheath
When constructed in accordance with EN 50290-2-1 and submitted to spark testing, communication cables may be installed together with Low Voltage cable
The tests are conducted following environmental and aging assessments, ensuring the cables' stability throughout their life cycle The raw materials used in these cables are specified in the EN 50290 series, which contributes to their durability and reliability.
Thus these cables are considered safe when:
− they are used for their intended purpose and applications;
− they are used under voltages and currents that do not exceed the limits given in the relevant specification
Fire reactions and Euroclasses
Cables that are installed in construction works are governed by the “Construction Product Regulation”; thus they shall be “CE” marked according to EN 50575
Moreover, in each country, regulations may exist that explain the use of cables according to a given Euroclass versus the type of building that is considered
When selecting cables, it is essential to choose those that meet or exceed regulatory standards, especially when safety is a concern Regulations and standards provide only the minimum requirements, so opting for higher-quality cables can enhance safety and performance.
Designers and installers must prioritize fire safety regulations when selecting cables Choosing cables that fully comply with these requirements enhances safety, particularly when the public or individuals are at risk.
The EN 50288, EN 50441, and EN 50117 product standards series reference the EN 50290 series to outline cable behavior in fire situations Specifically, EN 50290-4-1 establishes the connection between Euroclasses and the corresponding test methods and limits.
Some local regulations/customer-requirements are stricter than the Euroclassification tables and therefore can and should be designed by discussions between the producer and customer
In the event of a building fire, cables located within walls, elevator shafts, or air-handling plenums can act as conduits for flames, spreading fire between floors or sections of the building Current standards allow engineers to assess the time it takes for these cables to pose a risk when exposed to fire This information is crucial for optimizing evacuation times and enhancing building safety management, ultimately ensuring the safety of all occupants.
Cables and wires, often encased in plastic, can produce smoke and harmful gases when burned This is crucial to consider, as these cables frequently run through ventilation system return spaces located above ceilings or below floors.
Electromagnetic behaviour
Cables can encounter various stray electric fields, often generated by motors in heating, ventilation, and air conditioning (HVAC) systems, as well as fluorescent lights, radio transmitters, and power transformers These stray fields are classified as electromagnetic interference (EMI) when they originate from electrical sources, and as radio frequency interference (RFI) when they stem from devices such as radios, mobile phones, radars, or microwave ovens.
In environments with strong electromagnetic interference (EMI) and radio frequency interference (RFI), additional shielding for cables is essential to maintain signal integrity One costly method for providing this shielding is to route cables through grounded conduits, which helps dissipate stray fields and prevent interference However, using conduits can be expensive and challenging to install.
The EN 50117 series that describes coaxial cables defines two classes of shielding effectiveness The
The EN 50117 series outlines various classes of shielding effectiveness for coaxial cables, with Class A being the most widely utilized This class features a "foil+braid" outer conductor, ensuring adequate immunity for the cable Utilizing Class A cables guarantees reliable performance under standard conditions Additionally, alternative shielding methods like foil-braid-foil or foil-braid-foil-braid can be employed, and higher shielding classifications may also be explored.
The coupling attenuation and transfer impedance specified in cable specifications characterize the electromagnetic behavior of twisted pair cables Coupling attenuation results from the combined effects of twisting and screening.
In twisted pair cables, the signal is applied simultaneously to both the 'a' and 'b' legs, but the voltage levels are opposite and 180 degrees out of phase This phase difference leads to the natural cancellation of emissions, effectively reducing interference from electromagnetic interference (EMI) and radio frequency interference (RFI) when the signal is reconstituted in a comparator.
On an other hand, keeping the cable twisted means that both of the wires in the pair are likely to be affected equally by the interference
To maintain optimal performance, installers must ensure that the twist of the pairs in cables is preserved when connecting the connectors If the inherent immunity from the twist is inadequate, it is advisable to use cables that include their own shielding for enhanced protection.
Two kinds of extra shielding may be provided:
− the first is an overall foiled screen (FTP) – (F/UTP);
− the second involves individually screened pairs within a cable with (SFTP) – (SF/UTP), (SSTP) or without (STP) an overall screen
EN 50174-2 describes well the mechanisms of each of the kind of twisted pair cables
A short summary for governing the choice of cables twisted pairs telecom cables would be:
− use unscreened cables whenever it is possible;
− use unscreened pairs cable with overall screen (FTP) if you cannot control the electromagnetic environment or to preserve your cable to be influenced by the installation conditions;
− use multiple screens cables (individually screened pairs SFTP or SSTP or specific cables) in case of harsh environment and when it is required by the transmission performances
There are reasons why STP/FTP are not employed everywhere:
Proper grounding of shielding layers is essential to reduce signal degradation Variations in ground potential across different network areas, often due to issues with the grounding system or varying power sources, can lead to the formation of ground loops These ground loops not only introduce interference but also pose potential shock hazards.
- STP is less flexible than UTP because of the shielding and is more difficult to install
In telecommunications, utilizing a closed metallic continuous pathway, as outlined in EN 50174-2, is generally comparable to employing a cable screen.
Figure 8 Twisted pairs cables Screen description
6 Criteria for the choice of the cables
Cable construction
Regardless of the construction, all cables contain certain common elements that are detailed in
- insulation to prevent short circuits between the individual conductors;
- spacers (dielectric) to preserve the electrical properties of the cable;
A copper conductor in a cable can be composed of a single solid copper core or a bundle of thin strands The advantages and disadvantages of each been discussed next
Some parts of the EN 50288 and EN 50117 series describe flexible cables manufactured with
EN 50290-2-1 gives tools to get the cable attenuation depending upon the size of conductors and their nature (stranded or not)
Insulation serves as a high-resistance material extruded onto conductors to prevent current flow between them, often referred to as dielectric or insulation This material significantly affects the transmission properties of cables, particularly at high frequencies.
Insulation materials come in various types, each offering distinct advantages and disadvantages Their performance is evaluated based on loss angle (at high frequency) and relative permittivity, with optimal cable behavior requiring both properties to be low and stable.
There are several primary categories of insulators:
(PVC) PVC easy to strip
Flame retardant Low frequency High loss angle and high permitivity Polyethylene Flammable
Halogen free High frequency Good loss angle and low permitivity Fluoropolymers High temperature applications, Flame retardant
High frequency Low loss angle and low permitivity
The type of insulation used depends on the intended application of the cable:
- for low frequency cables, PVC according to EN 50290-2-21 may be used
There are several types of materials used for sheathing, each having its advantages and disadvantages:
(PVC) PVC easy to strip
Flame retardant PVC allows for bright colors
Depending upon the detail specification resists to UV, ozone, oil and solvents Polyethylene Flammable
(Outdoor applications) Water proofed Depending upon the detail specification resists to UV, ozone, oil and solvents Halogen free sheathing compound
Flame retardant Low smoke emission Halogen free
Depending upon the detail specification resists to UV, ozone, oil and solvents Fluoropolymers High temperature applications Flame retardant
Water proofed Resists to UV, ozone, oil and solvents, acid, contaminating fluids
The type of sheathing used depends on the intended application of the cable:
- EN 50290-2-27 describes suitable halogen free sheathing compound;
Some cables are manufactured with a metallic (or non-metallic) armour to provide added strength and protection against rodents and mechanical damage, usually required when burying direct
Cable that is used in outside plant or underground, may be filled with a waterproof gel compound and may have a water blocking tape between the inner and outer sheaths
Both outer and inner sheaths are made of materials designed to withstand immersion and resist corrosion
The cable's compliance with environmental specifications is outlined in the relevant documentation For specific settings, such as industrial environments, customized cables may be necessary, designed according to a detailed specification established between the customer and the manufacturer, in accordance with EN 50288-11-3.
Cabling
Cabling involves a systematic design rather than just a random assortment of cables It is important to distinguish between cables installed within the protective confines of buildings and those that are subjected to outdoor conditions.
Indoor cables run inside buildings, they need to be flame or fire retardant
They often have smoke requirements (density, opacity, acidity, halogen contents)
Certain applications involving Human Hazards or Data Hazards necessitate the use of fire-resistant cables In such instances, it is essential for the cables to undergo testing in compliance with EN 50200 standards.
Outdoor cables are usually manufactured with a stronger, denser sheath material
They have improved resistance to moisture and water penetration as well as enhanced mechanical and electromagnetic properties
They may be provided with an aluminium shield under the outer sheath They may be filled with water- resistant gel and covered with a layer of armouring
Table 3 Types of cabling according to applications
Application Indoor cabling Outdoor cabling
LAN EN 50288 series EN 50288 series PE sheathing
Access network EN 50407 series EN 50406 series
EN 50117-2-5 CATV (Drop cables) EN 50117-2-1
EN 50117-2-5 CATV (Trunk cables) EN 50117-2-3 EN 50117-2-3
Transmission performance
Transmission efficiency refers to the signal degradation caused by a specific transmission medium, which acts as a barrier to communication signals This barrier can be assessed through various factors, leading to a common inquiry: how far can the communication signal energy travel before it becomes too weak or distorted to be usable? While there is equipment designed to extend the transmission distance, it increases both the cost and complexity of deployment.
Data transmission quality is heavily influenced by the quality of cable pairs, as defined by the CLC/TC 46X specifications, which specify cable performance up to certain frequencies Poor quality pairs can lead to interference from neighboring wires and external sources, resulting in unintelligible data due to attenuation In such cases, missing data must be retransmitted Enhancing media quality reduces missed messages, minimizes retransmissions, and decreases unnecessary network traffic.
Cables standards have been developed in support of the cabling described in the EN 50083 and the
The EN 50173 series and ETSI recommendations are essential for ensuring that targeted applications function effectively when cable installations meet the standards set by the EN 50174 series.
The EN 50117 series, the EN 50288 series and the EN 50441 series sort the cables according to their maximum frequency and thus are suitable for well known existing applications
Table 4 Cables for CATV / MATV / TV and Video distribution
EN 50117-2-1 1 000 MHz EN 50083 series Indoor drop cabling
EN 50117-2-4 3 000 MHz EN 50083 series Indoor drop cabling
EN 50117-2-2 1 000 MHz EN 50083 series Outdoor drop cabling
EN 50117-2-5 3 000 MHz EN 50083 series Outdoor drop cabling
EN 50117-2-3 1 000 MHz EN 50083 series Trunk cabling
EN 50117-4-1 3 000 MHz EN 50173-4 Indoor drop cabling
Table 5 Cables for access network
Table 6 Cables that might be used for some given applications
EN 50288-2-1 100 MHz EN 50173-2 100 Base T2/1 000 Base T4 Screened
EN 50288-3-1 100 MHz EN 50173-2 100 Base T2/1 000 Base T4 Unscreened
EN 50288-4-1 600 MHz EN 50173-2 10 GBase-T Screened
EN 50288-5-1 250 MHz EN 50173-2 100 Base T2/1 000 Base T4 Screened
EN 50288-6-1 250 MHz EN 50173-2 100 Base T2/1 000 Base T4 Unscreened
EN 50288-7 Instrumentation and control cables Screened
EN 50288-8 2 MHz EN 50090 series Type 1 cables characterized up to
EN 50288-9-1 1 000 MHz EN 50173-2 10 GBase-T Screened
EN 50288-10-1 500 MHz EN 50173-2 10 GBase-T Screened
(all parts) 500 MHz EN 50173-3 10 GBase-T Unscreened
EN 50441-1 a 100 MHz Residential 100 Base T2/1 000 Base T4 Unscreened
EN 50441-2 a 100 MHz Residential 100 Base T2/1 000 Base T4 Screened
EN 50441-3 a 1 000 MHz Residential Cable sharing 100 Base
EN 50441-4 1 200 MHz EN 50173-4 Cable sharing 100 Base
T2+VHF/UHF+DSL Screened aThese cables are optimized for 50 m residential cabling.
Delivery
Before laying the different cable sections, all reels should be visually inspected for possible transportation damage
Storage
Never forget to place a wedge under the flange to avoid reels rolling away
When cable is stored outside, a cap shall be placed at both ends to avoid water infiltration
Storage temperature range is specified for each cable and shall be respected
Indoor cables shall not be stored outside to prevent water infiltration and UV damages
If several reels are stored at the same place, take care that flanges of a reel don’t collide with cable of another reel
Pre-installation procedure
Unless otherwise specified by the cable manufacturer, never install a cable if temperature is below –
When installing cables in cold environments, typically around 5 °C, it's important to note that the cable sheaths become stiffer and more prone to damage from bending and pulling The recommended installation temperature range for cables is significantly narrower than their operating temperature range.
Before pulling the cable, ensure the stability of the pay-off:
To avoid possible damage from a sudden stop, the pay-off shall be equipped with a progressive braking system Under no circumstances should the reel be stopped by hand
The route defined by the design should be accessible and available in accordance with the installation schedule The users should be advised of all proposed deviations
The installer must verify that the environmental conditions along the installation routes and the chosen installation methods are appropriate for the cable being installed, as specified in the cable's datasheet.
When a route includes areas where cables may be exposed to high temperatures, it is essential to implement appropriate protective measures Pay special attention to heating pipes, particularly those that are not continuously heated.
Any measure necessary should be taken to prevent the cable experiencing direct stress following installation
The installer should determine the locations at which reels are to be positioned during the installation program
Where necessary, the minimum quantity of ceiling tiles, floor covers should be removed and always replaced.
Pulling of the cable
For reasons of safety, always unroll cable by the bottom side of the reel
During the pay-off of the cable the off-loading of the reels should be monitored to ensure that no mechanical damage occurs (kinking, unravelling or twisting)
Figure 11 Advised way for pulling a cable
Installation
It is advisable to leave several meters of cable as a reserve at both ends, along with an additional 5 meters of extra cable at various points along the cable link This practice facilitates easier repairs in the event of a cable break.
Always cut first meters of cable off as this part can be damaged by pulling of the cable, bending, water, etc
Ripcords are designed to make removal of the exterior cable sheath easier, preventing unnecessary stress to the core.
Mechanical considerations
One of the goals in any cable installation is to complete the installation with as little stress as possible to the conductors themselves
All cables come with a precisely determined tensile loading value that must not be exceeded The tensile strength indicates the maximum load a cable can withstand without compromising its core characteristics It is important to note that this value is not the breaking strength of the cable, but rather a practical limit for safe use.
Pulling cable through, over, or around stationary objects like ducts, corners, and conduits can introduce additional stresses To prevent excessive force during installation, many installers carefully monitor the pulling tension Once installed, the cable experiences lower loads, known as the installed, long-term, static, or operating load.
The tensile strength of the cable will depend upon the cable construction, and the application for which it is designed You will find values in the relevant cable specification
The EN 50288, EN 50406, EN 50407, and EN 50441 series establish the maximum tensile strength based on the copper section in cables Unless the customer specification indicates otherwise, which may include additional strength members, the tensile strength values provided in these standards must not be exceeded.
The minimum bend radius, established by the cable manufacturer, indicates the smallest bend a cable can endure Exceeding this recommended bend limit may lead to impedance disturbances and crosstalk.
Figure 13 Shrinkage and elongation of internal and external element
Like tensile strength, there are two values associated with bend radius, installation and long term
The installation bend radius refers to the maximum bending the cable can endure during installation Once the cable is installed and the pulling stress is alleviated, it can be bent to a smaller radius These bend radius values vary based on the cable's size, construction, and intended use.
R’ a) b) c) Figure 14 Common handling mistakes when bending cables
Common handling mistakes can lead to exceeding cable bend radii, with one of the most frequent errors being the pulling of cable through conduit that has an insufficient bend radius.
Similarly, cable shall never be over-bent going through trays, between tray sections, or when making transitions between locations
To ensure optimal performance, cables must be 'swept' to avoid sharp bends or corners, as bending them tightly can lead to significant damage It is crucial to refrain from wrapping cables tightly around themselves or stuffing them behind walls, as this can also compromise their integrity Cables should never be kinked or knotted to maintain their functionality.
Cable crush and impact are critical yet often misunderstood aspects of cable installation The EN 50289-3-9 standard outlines a specific crush test method to evaluate a cable's ability to endure or recover from slow crushing forces This document provides a comprehensive testing procedure, which involves compressing a cable between two plates while monitoring power loss and impedance changes.
Impact testing evaluates a cable's capacity to endure repeated impact loads, particularly in exposed installation areas This testing is crucial not only for assessing changes in transmission characteristics but also for understanding how cables perform under real-life conditions The significance of crush and impact testing extends beyond laboratory standards, reflecting the practical challenges faced during installation.
To prevent damage, it is crucial to avoid applying excessive crushing forces on cables by utilizing specialized products that prevent over-tightening Additionally, regularly readjusting cable fixation and bundle formation is recommended.
Figure 15 Crush and impact testing
In office environment work area cables are often subjected to crushing (human step or worst rolling chairs) It should be noted that:
- ‘standard’ cables are designed to withstand to a human step; however it is recommended to avoid this stress using additional protective carpet;
Strength indication to prevent over- tightening and compressing cables
Possible manual release to adjust strength or add cables
- ‘standard’ cables do not withstand to the stress of a rolling chair.
In residential homes, proper cabling often involves stapling the cables securely However, if the staple size does not correspond correctly to the cable diameter, there is a significant risk of damaging the cable.
The EN 50441 series describes cables that are tested for stapling
To avoid transmission problems due to resonance phenomena, it is however strongly recommended to randomly space the staples along the cable a) b) c) Figure 16 Cable stapling
Outside plant
Much of the truly long-haul cable pulled is for trunk or telephony applications, and is installed by trained professionals using special and expensive equipment
Routine cable installations often involve some outdoor cable runs, which can range from extensive lengths on campus applications to shorter segments, such as a 20-meter connection between two buildings.
Cables designed for long-haul buried applications are engineered to endure various stresses, featuring gel filling that effectively prevents water migration The use of specially selected sheath materials ensures abrasion and UV resistance, while outside plant cables boast high tensile strengths to withstand environmental challenges and the demands of direct burial installations.
Trenching is the process of excavating a hole to install a cable, followed by refilling the trench Typically, backhoes are used for digging, and the trenches are inspected for any rocks or debris that may harm the cable To ensure optimal protection, it is advisable to place 20 cm of sand both beneath and above the cable.
Figure 17 Cable buried in a trench
Burying cables is a meticulous process best suited for shorter distances, requiring sufficient depth for protection The necessary burial depth varies based on the cable's application, intended user, and construction To enhance safety, it is advisable to bury cables below the frost line specific to the region A significant risk for buried cables is accidental excavation, so placing a marker tape above the cable but beneath the soil is recommended to alert future workers Additionally, some armored cables are designed to be resistant to rodent damage.
Figure 18 Cable buried in a trench with a warning tape
The conduit utilized in outside plant applications not only protects cables but also provides installation benefits Manufactured from rigid and abrasion-resistant materials, underground duct or conduit is designed for burial In urban areas, a network of ducts is often installed beneath streets, accessible via utility vaults or manholes This installed conduit facilitates the installation of new cables or the removal of old ones without causing damage to streets, pavements, or buildings.
To facilitate future installations, conduits should be equipped with a pull rope or tape during placement Additionally, in trenching operations, conduits are often installed alongside direct burial cable to ensure readiness for future use.
Inner duct, a less sturdy plastic tubing designed to fit within larger conduits, plays a crucial role in cable management While it does not provide primary protection for cables, it aids in cable identification and maintenance through various colors offered by manufacturers Inner duct creates a clean pathway for new cable installations, addressing the challenges of pulling new cables alongside existing ones, which can lead to friction and blockages By keeping cables separate, inner ducts help prevent damage during future installations.
Figure 19 Conduit for underground burial
Conduits provide effective rodent protection in short inter-building installations where splicing to armored cable is impractical They can be installed economically in situations where additional trenching is not feasible, such as under concrete banks, landscaping, farmland, or private properties This method minimizes soil disturbance over time, allowing for the selection, addition, and installation of cables later without disrupting the surrounding environment.
Cable pulling is the primary technique for installing cables into conduits Initially, a pulling tape is inserted into the conduit, after which the cable is securely attached to the tape Finally, the cable is drawn through the conduit using the pulling tape.
Cautions: Always respect the minimum bending radius and never exceed the maximum pulling force value specified in the cable data sheet
Aerial cable installations involve complex details, but several key points can guide the process Similar to direct burial installations, utility companies typically use specialized equipment for long-distance aerial runs However, in campus or industrial settings, shorter links between buildings can often be more efficiently installed aerially.
Figure 20 Example of an aerial cable installation
Figure 21 Cable ‘messenger clamp/grip’
Aerial cables are susceptible to wind and ice, which can lead to stretching or sagging To prevent these issues, it is essential to support aerial cables with an external support member, such as a suspension strand or messenger.
Steel wires are securely attached to utility poles along the designated route The cable is positioned beneath the messenger wire, lifted into place, and fastened using steel or dielectric thread Standard lashers are utilized for the lashing process, and the choice of lashing strands should align with the guidelines for the lashing tool Typically, it is recommended to have at least one wrap of lashing wire for effective securing.
When selecting messenger wires, it is essential to consider their tensile strength, size, and the span distance based on the specific application requirements Recommended charts for messenger strands are easily accessible However, various factors must be evaluated, as the inability to install a dedicated messenger can negate the advantages of a well-established system.
Intrabuilding
Inside a building it is strongly recommended to select a cable with a LSZH-FR sheath
Intrabuilding conduit systems offer flexibility in installation, as they can be placed in ceilings, walls, or under floors However, they are best suited for permanent workstation outlet locations where no flexibility is needed and where density is low It's important to note that under-floor conduits, often embedded in concrete, pose challenges for future modifications or relocations.
Figure 22 Examples of installation of intrabuilding conduits
Pull cords should always be placed in the conduit to ease installation Inner duct is an excellent tool for protecting cables and making future installations easier (Figure 22 b))
8.2.3 Dropped ceiling and raised floor
Plenum or dropped ceilings and raised floors are often the simplest options for installation, as they feature easily removable panels that allow for quick access to the space This method is particularly popular in new buildings, where dropped ceilings are commonly used for cable installation While raised floors are typically found in computer rooms, they can also be utilized in various other settings.
Suspended ceilings are lightweight panels held up by metal frames or grids attached to the ceiling with struts or wires These panels can be easily moved; when pushed up, they detach from the grid and can be shifted to the side While not generally advised, smaller cables may rest directly on the ceiling support grid at the installer’s discretion.
Cables should be supported in some manner, ideally in organized, easy-maintenance trays, wire ways or racks
At the very least cables can be supported by bridle rings
Cable trays, also known as "ladder racks," offer a safe and efficient solution for cable installation, suitable for ceilings, floors, and riser shafts Some trays are designed to be visually appealing for installation below the ceiling while accommodating various cable types Typically, tray installation occurs before cable installation, allowing for a pre-existing distribution system in many buildings, which can facilitate clear routing for new cables.
While trays offer robust support and basic protection for cables, they still face various stresses Cables should be installed in trays to minimize tension, crushing, and excessive bending It's essential to inspect routes for sharp turns, snags from other cables, or rough surfaces Care should be taken to avoid running cables beneath or between heavier or multiple cables that could exert additional forces This principle also applies to moves and additions Securing cables to the tray is advisable to prevent damage during future modifications.
Support the cable and avoid crushing, stressing and over-bending it Every cable will have values attached for minimum bend radius and maximum
In addition to monitoring the cable pulling tension, additional efforts to support and protect the cable will greatly lengthen its working life
Cables should never be allowed to hang freely for long distances or be allowed to press against edges in any installation
To ensure a smooth transition when pulling cable in conduit, it is essential to maintain all transition points, such as those leading to a pull box, in a seamless manner Adding an extra piece of conduit beyond the transition can prevent the cable from resting on sharp edges, enhancing the overall integrity of the installation.
Bushings designed to fit the ends of conduit are also available
Flexible conduits are essential for protecting cables from pressure and abrasion, especially when installed within boxes or at interfaces They are particularly beneficial in high-traffic areas, such as raised computer room floors, where the risk of damage to the cables is greater.
Adhering to the cable's minimum bend radius is crucial, as improper bending can lead to damage in various applications It is essential to take precautions to prevent conditions that may compromise the cable's integrity due to equipment configuration or bending.
When installing conduit bends, pull boxes, and joints, it is essential to ensure that the radius is not excessively small To facilitate the routing of cables around tight corners, inner duct or flexible conduit can be utilized The inside radius of conduit bends should be a minimum of 10 times the inner diameter of the conduit For tightly bent elbow fixtures, cables should be back-fed rather than pulled from end to end; instead, they should be coiled loosely on the ground and then fed through the remaining run Additionally, in tray and rack installations, it is crucial to monitor the minimum cable bend radius as cables navigate around corners and transitions.
To ensure cable protection at raceway or rack transitions, it is essential to use flexible conduits Similar precautions should be taken when installing cables in vertical shafts or risers, where it is crucial to adhere to proper bend radii and tensile loading limits Additionally, cables in vertical runs must be adequately supported at multiple locations to maintain their integrity.
Figure 23 Example of mistake in pulling cables in conduits
Generally, cables with PE sheath cannot be glued
In many network cable installations, cables can often be pulled by hand over short distances and straight paths, eliminating the need for special equipment It is crucial to ensure that any load applied to the cable is directed towards its strength-bearing members.
When extra mechanical force is needed to pull a cable, various standard tools can assist in the installation process External pulling grips are specifically designed to securely lock onto a cable and tighten as tensile load is applied The pulling end of these grips features a loop or eye for easy attachment of a pulling tape or rope.
Figure 25 Advised way for pulling a cable
Using a swivel during cable pulling is essential to prevent twists in the pulling tape or rope from affecting the cable It's crucial to monitor the tension on the cable to avoid exceeding the maximum installation load Additionally, cutting the cable back by 3 meters from the pulling end can help eliminate any sections that may be damaged during the installation process.
Once the cable has been properly pulled and secured, it is ready for connectorization or termination Ensure that there is sufficient spare cable at both ends to reach the designated work area, especially if it needs to extend into a clean room in certain environments When planning the cable length, take this additional distance into account Prior to termination, it is advisable to cut off approximately 3 meters of cable to eliminate any sections that may have experienced stress during the pulling process.
After cable pulling, if the cable is not directly terminated, it is absolutely necessary to replace a cap at both ends of the cable in order to avoid water penetration
In case of partial use of a cable, both ends of the remaining cable shall be fastened to a flange of the reel by means of a ‘bridge nail’
The 'bridge nail' must not exceed the thickness of the flange to prevent injury from 'nail nibs' and to protect the remaining cable on the spool.
Figure 26 Example of cable pulling when a mechanical force is required