This is the second in a series of posts where we offer guidelines on how to produce a specification for an IT cabling system. Today we review industry standards, the types of cable available, and the capabilities of copper and fibre.
Cabling systems are often specified using USA standards, e.g. Cat 5e or Cat 6. However, you should get assurance from your installer that your new cabling system will comply with your country’s structured cabling standards. For the purpose of this document we are using BS EN (British Standard, European Norm) standards, namely:
- BS EN 50173 series for performance and components
- BS EN 50174 series for design, installation, operation and maintenance
- BS 6701 for installation, operation and maintenance
- BS EN 50310 for grounding and bonding
- BS EN 50346 for testing.
The standards specify a range of Classes or Categories of copper cabling systems, correctly referred to as balanced cabling systems. Amongst these are:
- Class D – Comparable with TIA Cat 5e, supporting Gigabit Ethernet (1000BASE-T)
- Class E – Comparable with TIA Cat 6, supporting Gigabit Ethernet (1000BASE-T) and 10Gigabit Ethernet (10GBASE-T) to a distance of 35m
- Class EA – Comparable with TIA Cat 6A, supporting 10 Gigabit Ethernet (10GBASE-T)
- Class F – Comparable with TIA Cat 7, supporting 10 Gigabit Ethernet (10GBASE-T)
- Class FA – Supporting 10 Gigabit Ethernet (10GBASE-T).
Choose a class that will meet your bandwidth requirements for the foreseeable future and that will fit within your budget. Bear in mind that higher class cabling is more expensive, and requires larger containment and pathways as the cables have a bigger diameter.
Choice of Cabling Medium
Bandwidth, lengths of cable runs, and environmental influences will determine your choice of cabling medium. In a typical enterprise installation, it is customary to use balanced twisted pair copper cables to service work areas although optical fibre cabling may be a better choice if security or electromagnetic interference are significant considerations.
Class D (Cat 5e), Class E (Cat 6) and Class EA (Cat 6A) cables are available as unshielded (UTP) and shielded (e.g. STP, FTP). Class F and Class FA have an overall shield only and each pair is individually foil-shielded. Unshielded cable is suitable for some installations but shielded cable may be required if high levels of electromagnetic interference are present or if a high “tempest” rating is required for security purposes. Also, in the case of Class EA, the unshielded variant has a larger diameter so requires larger containment.
The following circumstances, commonly found in backbones, may make it necessary to select optical fibre cabling:
- If the length of a cable run is over 90m
- If each end of the cable terminates in different electrical earth zones. This is often the case if nodes are in different buildings – a non-metallic optical fibre cable is far less likely to conduct damaging electricity in the event of a lightning strike
- If the cable is routed externally. In this case sheaths need to be more rugged and weatherproof. This is more often available for optical fibre cables
- If the space in the cable containment is limited; a multi-core fibre can carry many times the volume of data cable
- If a high level of security is required; optical fibre is secure against unauthorized access.
Selecting the Right Optical Fibre Cable
The selection of OM1, OM2, OM3, OM4 or OS1/OS2 optical fibre cabling depends on the network application and the distance. OM1-OM4 cables are multimode whilst OS1 and OS2 cables are singlemode.
*Distances listed are industry minimums.
Mechanical Protection and Physical Properties
The selection of cable sheath material such as PVC, Low Smoke Zero Halogen (LSZH) or plenum rated, depends on the attitude to risk, local regulations and the requirements of other interested parties e.g. premises owners and insurance companies.
Optical fibre cables may need to be armoured and rodent-resistant to give protection in ducts or for direct burial.
Lifetime Cost Effectiveness
A cabling system represents the element of a network that has the longest life span so should be designed and installed with at the very least 10 years of useable life. To ensure consistent performance throughout the life of the system, the following should be considered:
- Warranty and performance guarantees from the component manufacturer
- Quality components proven to meet appropriate standards
- Manufacturer and supplier support
- The installers have relevant qualifications and training and their installation methods fully comply with country standards.
Depending on your knowledge and the complexity of your requirement, expert assistance may be needed to complete the specification.
Watch out for future posts on how to specify an IT cabling system, including:-
- Cable Pathways, Installation Techniques and Documentation [Part 3]
- Testing of Copper and Fibre Links [Part 4]