Fiber optics: a backbone for advanced building design

Fiber-optic cables are an integral part of a building communication system. Although they are commonly installed for the enterprise network communication, they are also designed into building-management systems and electrical-power coordination.
By Tim Kuhlman, PE, RCDD, and James Godfrey, CH2M, Portland, Ore. August 25, 2015

This article has been peer-reviewed.Learning Objectives

  • Assess when and where to specify fiber-optic cable
  • Classify the three different core sizes of the fiber-optic glass, which impact its performance.
  • Summarize the cable listings recognized by the NEC and the scenarios of when the cable can be routed with power and other circuit types.

In the language of the information and communications technology (ICT) professional, fiber-optic cabling is the backbone medium for transporting data across campuses and through the spine of buildings. This in itself is not new. Fiber-optic cabling has played an integral part in network construction since the 1980s. Every year we continue to see advancements in technology, which in turn create more data and therefore highlight the role fiber optics plays for data transport. As a corollary to Moore’s Law, which describes the doubling of transistors per integrated circuit every 2 yr, there is a corresponding increase in the amount of data generated that then is transported.

Figure 7: The Saudia Sinnovate Smart Technology Hub in King Abdullah Economic City, Saudi Arabia, is shown. Courtesy: CH2MIn the 1980s, data transported from mainframe computers, mini-frame computers, and the early local area networks (LAN) connecting business workstations. In the 1990s, mainframes were rapidly being replaced by file servers communicating with desktop computers. E-mail and file transfer generated a lot of the network traffic. During this decade, access to the Internet and Web became available in the office. There was rapid growth in data transport as the content of the Internet evolved from text to graphics, audio, and occasional video. In the 2000s, video on the network continued to increase. We also saw the migration of telephone voice communications from private branch exchanges (PBXs) using large copper backbone telephone cables to Voice over Internet protocol (VoIP), which uses the data network infrastructure.

This brings us to the 2010s. Streaming video on the network is commonplace, and the Internet is so pervasive that it is not evident if data is being sourced from the enterprise network or the “cloud.” Access to office networks is expected to be ubiquitous in every building. Not having access can leave one feeling detached.

Through this evolution of computing and networking, there has been a parallel evolution in building design. It started with the automation of manufacturing and business processes; in other words, it started with the internal operations for which the buildings provided shelter. We are now witnessing the start of fully integrated and automated buildings. As we design advanced intelligent buildings, they are generating their own data to add to the network load.

Table 1: The table provides a summary of the different fiber types, bandwidth, and attenuation values recognized by TIA 568.C3 and C3.1. The table was created by CH2M from data extracted from Standard TIA 568.C3, 2008, Table 1, and TIA 568.C3.1, 2011, TabThe data generated by the building infrastructure is also related to the next emergence of data to be transported referred to as the Internet of Things. This term is attributed to Kevin Ashton, who in 1999 used it to describe embedded logic in physical items that can communicate with other devices beyond their own systems. Of course, the data generated by a building is only a fraction of what is expected to be generated by the occupants of the building. Everyday items occupants bring into the building will generate data. This is more than just tablet computers and smartphones. In the next few years we will see a new category of generated data from disposable logic devices. For example, imagine a disposable food container that has logic to identify when the contents is approaching its expiration date. The logic communicates with a smartphone that can upload the information to the cloud and then is accessed by an application on the smartphone.

Another technology component with large impacts on data is the proliferation of cameras in tablets and smartphones. This technology has a twofold impact. Video generates large data streams that are being used by more applications, and as the technology continues to improve for the devices, the video definition increases, which also increases the data stream size. All of this is generating more data, which is being backhauled (or transported) by the fiber-optic backbone.

Whether it is a route across town, between buildings on a campus, or between the communication rooms throughout a building, fiber-optic cable is the preferred backbone cable medium for data transport. Sending a signal is faster when using radio, but radio cannot match the bandwidth of optical fiber. Copper cabling is still an option for short data links, but cannot compare to fiber for the longer data channels. Fiber-optic cable is so widely used that for the purpose of this article, we will focus on cabling used for enterprise and facility building systems. This includes fiber-optic cable for LANs, passive optical networks (PON)s, control systems, monitoring, and security systems. To properly specify the cable, it is necessary to consider the type of communication link, the bandwidth requirements, strand count, and the environment in which the cable will be installed.

Optical fiber versus copper

Copper cable technology has worked hard to keep pace with the continuing increases in network bandwidth requirements. The current high-speed copper cabling standard in the U.S. is a Category 6A unshielded twisted-pair cable. It is rated at a frequency of 500 MHz and bandwidth that supports 10-GB/sec Ethernet for a standard cable length not exceeding about 100 m between network devices. This is more than adequate for most office desktop workstations and even backbone cabling in small buildings where there are one or two communications rooms not exceeding the 100-m cable length.

Table 2: This is a summary of the NFPA 70 National Electrical Code (NEC)-recognized fiber listing designations and the allowable substitution of one listing type for another. The table was created by CH2M from data extracted from NEC 2014 Table 770.154(b)However, the predominant copper cabling being installed today is a Category 6 cable rated at 250-MHz frequency, which supports 1-GB/sec Ethernet. The bandwidth requirements at the desktop do not yet exist where we have passed the tipping point of requiring this higher bandwidth cable. For a typical hierarchal LAN design, copper cable to the office desktop is less expensive than a fiber-optic cable. Just as hard as the copper industry has worked to increase the bandwidth (i.e., longevity) of their product, the fiber optics industry is working to bring down the cost of their products.

There are a number of limitations for copper cabling, one being the 100-m channel distance. This ideally serves as the connection point between the communication-room network equipment and the desktop workstation (or another network-connected device). Copper cabling is more susceptible to electromagnetic interference (EMI) noise than fiber-optic cable, although our engineering team has routed unshielded Category 5e and 6 cable in high-EMI-generating manufacturing environments, and it has performed with no noticeable degradation in network performance.

Copper cable is susceptible to thermal noise generated in the cable from routing the cable in high-temperature environments. From a security standpoint, copper cable is less secure. The signals traveling along the cable generates radio frequency (RF) radiation which can be detected.  However, fiber-optic cable is not impervious to signal tapping. Although a fiber-optic cable does not radiate an RF signal like a copper cable, a very skilled technician can expose a single strand of optical fiber in a cable, and the fiber can be bent to allow some of the light to escape. This may sound far-fetched, but fiber optic technicians that splice fiber-optic cable actually use a similar technique to inject light and siphon light from a fiber strand while splicing the cable to measure the quality of the splice.

Fiber-optic glass, which is an excellent dielectric, is effective in providing electrical isolation for the data circuits connected between different buildings on a campus or between communication rooms spread widely apart in a building. The entire cable can be made of dielectric materials, which requires no bonding or grounding. This can help in providing electrical noise isolation for the network equipment and to avoid ground loops.

Even though there is not a lot of Category 6A cabling being installed at the workstation level, within the Telecommunications Industry Association (TIA) Standards body there are people working on a Category 8 cable that is proposed to have four times the Ethernet bandwidth of the Category 6A cable. For now, and the foreseeable future, for a typical hierarchal LAN fiber-optic cable will continue to dominate the building backbone, and copper cable will continue to dominate the segment-to-the-workstation outlet. An exception to this is a non-hierarchal LAN called PON, or passive optical networking. In a PON network, the entire cable plant distribution consists of fiber-optic cable.

Table 3: This sample calculation illustrates how to calculate the number of strands required in selecting the size of a fiber-optic cable. Courtesy: CH2MA true advantage copper cable has over fiber optics is the ability to transmit power from a communication room to a device. Power over Ethernet (PoE) is a technology allowing a variety of devices to be powered using the same data cable that is used for data transport. There is not enough power in a light signal in a fiber-optic cable to power a device. Fiber-optic end equipment still needs to rely on copper cables for this.

Communications and control

The largest use of fiber-optic cable in a typical commercial building is for enterprise networks. For industrial and manufacturing facilities, the networks supporting building and manufacturing automation may dominate the enterprise network. For other complex facilities such as a data center or an innovation hub, the building automation system (BAS) can be a significant portion of the enterprise network infrastructure, which is often completely isolated from the data center production network. Instead of a manufacturing-automation network, these types of facilities have networks supporting the data center’s data traffic and collaborative information, respectively.

For industrial and manufacturing facilities, the networks can be categorized into three major groups: office automation, facility automation, and factory automation. Office automation is what we are most familiar with; it includes such services as e-mail, time entry, billing, and other office utilities you would typically access from an office desk. The facility-automation networks provide data services for controlling and monitoring building equipment such as air-handling equipment, lighting control, power monitoring, UPS monitoring, and battery monitoring. For light industrial and commercial buildings, the facility-automation system would typically use a direct digital control (DDC) system.

In an industrial or manufacturing environment, complicated or custom requirements typically require the use of a programmable logic controller (PLC) or distributed control system (DCS). For DDC, PLC, and DCS data is generated for monitoring and control by a supervisory control and data-acquisition (SCADA) system.

The last network category is factory automation, which only exists for manufacturing environments. This includes data generated by manufacturing equipment directly or in “work in progress” stations associated with the manufacturing equipment. The data generated could relate to supervisory monitoring of the manufacturing tool, tracking inventory, tool metrology, or an alarm status.

What all of these networks have in common is that they are using Ethernet as the communication protocol and can be supported by the enterprise information technology (IT) network. The cabling infrastructure provided by IT can handle network protocols other than Ethernet, but the network equipment and architecture typically would not. The IT network may be able to provide a couple of fiber strands in the fiber backbone for a Modbus serial link, but this would not be data going through the IT Ethernet network equipment. IT staff members will design and support the network architecture to provide bandwidth allocation and network segregation between the different networks it hosts. They may choose to physically segregate the networks by allocating separate network equipment and fiber strands for each network type, or multiplex the data onto a few fiber strands using virtual LANs (VLANs) to isolate the network traffic. This is important to note because the network architecture is what determines the cabling architecture and, consequently, the type of fiber-optic cable along with the number of fiber strands that are needed.

Security systems such as access control and closed-circuit television (CCTV) may or may not be included in the enterprise networks. This depends on the building owner and the security plan. The trend in security equipment is to migrate away from analog and proprietary communication protocols to IP-based devices. Often the devices, such as cameras and card readers, are Power over Internet-enabled, allowing them to be powered by the same network cable that provides the data transport. Buildings fall at both ends of the spectrum—from completely segregated security networks, where they have their own network switches, rooms, and backbone fiber cable, to systems where security is just another device on the enterprise network with their own VLAN.

Facility-automation and factory-automation networks rarely reside on the enterprise network. In a control system, designing the SCADA may be on the enterprise network; but the peer-to-peer communications from PLC to PLC or PLC to remote input/output (I/O) panel is on a separate network often using industrial-rated network switches. Control networks may or may not use the Ethernet protocol for communications even though they are still connected with fiber-optic cable.

Optical fiber types

What is common among the enterprise networks, automation networks, and proprietary communications circuits using fiber-optic cable is they all use “standard” fiber-optic cable. These are the cable types defined by the ANSI/TIA Standard TIA-568-C.3-2008, The Optical Fiber Cabling Components Standard. This standard is part of a suite of standards developed by the TIA TR-42 committee and subcommittee relating to communication-structured cabling. The cabling manufacturers design their products to meet these standards, along with the electronic manufacturing companies producing the network or communication devices that will connect to the cable. Ideally, if the manufacturers, network architects, ICT engineers, and installers all follow this suite of standards, the system components will be compatible. .The cabling infrastructure will fully support the network equipment.

Table 1 is a summary of the fiber types described in Standards TIA-568-C.3 and the addendum TIA-568-C.3.1. There are four types of multimode fiber-optic cable defined as OM1, OM2, OM3, and OM4, along with two types of single-mode fiber defined as OS1 or OS2. It should be noted that a designation such as OM3 is actually a designation provided by the international standard ISO/IEC 11801 and is only referenced by the TIA Standard. Unfortunately, the designation provide by TIA for the OM3 cable is TIA “492AAAC.” Both cables meet the same performance requirements, but it is easier to say “OM3” than to use the TIA designation.

Figure 1: This represents the different standard fiber-optic core sizes and provides the dimensions of the fiber core and cladding. Courtesy: CH2MThe optical-fiber types have different performance characteristics. Each fiber type has a different usable optical wavelength, maximum attenuation for a given cable length, and characteristic bandwidth for a given channel length. The network architect and ICT engineer take this into account when selecting network components and cable for a particular design. It is not as easy as just selecting the cable with the largest bandwidth and the longest channel distance. Operating distance and bandwidth come with a cost. For example, the OS2 fiber-optic cable will provide the maximum distance and maximum bandwidth. Because this is single-mode fiber, which has a very small core size, the optical transmitters are lasers, which are more expensive than the LED or vertical cavity surface-emitting laser (VCSEL) transmitters used with multimode-type cable. Since this cable and associated optical transmitters are designed for long distances, the signal at the receiver may have to be attenuated for short cable segments.

Per the standard, all of the fiber types have an outside diameter of 125 microns, and all the fiber types are glass. The fiber is manufactured in a way to provide a different index of refraction at the fiber core than the outer cladding. When the fiber is connected to a light source, the light is injected into the core. It is refracted and reflected within the core as it propagates down the fiber. Figure 1 shows the cross-sectional area and the different core sizes for the standard optical-fiber types. OM1 is a legacy fiber type with a core size of 62.5 microns. It is still manufactured to provide support to existing cable plants with this type of fiber. Most new cable plants using multimode fiber will be specified with one of three grades of 50-micron fiber (OM2, OM3, or OM4). Single-mode fiber has a relatively smaller diameter when compared to multimode fiber, with a nominal diameter of only 9 microns.

Multimode fibers can accept more light due to the larger core than a single-mode fiber. This is an advantage when using LED and VCSEL light sources, which have less power and are significantly less expensive to manufacture than a laser. One drawback of the relatively large aperture of multimode fiber is that it allows multiple light path vectors (modes) for the light to travel. A ray of light entering at exactly 90 deg to the end surface and in the very center of the fiber core will travel a shorter distance than a ray of light entering the core at an angle and reflecting off the core cladding surface as the light travels down the fiber. If this was a pulse of light from an LED, which can generate multiple light vectors, the different modal paths would cause the pulse to spread out as the light propagates down the fiber. Eventually the pulses spread out so much that one pulse cannot be distinguished from another pulse. This is referred as modal dispersion and is a limiting factor in the bandwidth of multimode fiber.

If you were to look at the core cladding separation for multimode fiber as shown in Figure 1, it would appear there was a stepped index of refraction difference between the core and cladding. The way the fiber is shown helps to illustrate the relative size difference between the core and cladding, but this is deceptive in showing the index of refraction profile of the glass. In all the multimode fiber types accepted in the TIA standard, the index of refraction profile gradually changes from the center core to the cladding. Keep in mind the index of refraction of glass is measured as the ratio of the speed of light through a vacuum divided by the speed of light in the glass.

Figure 2: A side view profile of the fiber demonstrates how different modes of light travel down the fiber-optic core and disperse the input light pulse. Courtesy: CH2MThe speed of light in a vacuum travels at approximately 3×108 m/sec. In the fiber-optic glass, the light may only travel at 2×108 m/sec. Fiber-optic glass manufacturers have developed techniques to manipulate the index of refraction in the core of the multimode fiber so that a mode of light takes a longer path; it will travel faster than the mode of light that travels the shortest path down the center of the fiber. This is referred to as graded index fiber. The effect of minimizing the pulse spreading is it allows there to be more pulses per second. which allows for a higher bandwidth (see Figure 2).

With “ideal” single-mode fiber, the core is so small that it only lets one single mode of light into the fiber. If there is only one mode of light, then there is no pulse spreading. For the “ideal” single-mode fiber, the fiber would have almost infinite bandwidth. Looking back at Table 1, you will note for single-mode fibers there are no bandwidth values listed. The bandwidth for single-mode is more a limitation of the optical transmitters’ and receivers’ capabilities than the fiber. The real world often differs from the ideal. In reality, there isn’t one single mode of light propagating down the fiber and, therefore, doesn’t have infinite bandwidth. There is a small amount of pulse spreading that does exist.

There are tradeoffs in selecting either multimode or single-mode fiber. Multimode optical fiber typically costs more to manufacture than single-mode fiber due to the graded index profile. However, it can use lower-cost light sources such as LEDs or VCSELs. The connector hardware for terminating the multimode fiber doesn’t have to be as precise as for single-mode fiber due to the larger core size, therefore the connectors cost less. Due to the pulse spreading and lower power of LED-type light sources, multimode fiber is best-suited for shorter distances at a high bandwidth (300 m for 10-GB/sec Ethernet) or longer distances at a smaller bandwidth (2,000 m for 100-MB/sec Ethernet). In the design of networks for campuses and buildings, the network architect and the ICT engineer will work together to identify the bandwidth required for each fiber path, the distance of each fiber path, the optical modules for the network equipment, and the type of fiber for each connection in the network.

Determining strand count

Determining the strand count for each backbone cable should take place after the network architecture has been planned. The network architecture will determine if separate fiber pairs are to be used for each network type, or if a virtualization of the network will be implemented resulting in fewer fiber strands.

  • Questions that need to be addressed include:
  • Will the system be designed with redundancy such that a secondary pair of fiber is required for each primary network circuit?
  • Does the network require very high bandwidth circuits, such as in a 40-GB/sec link, where eight strands of fiber are required for each network circuit?
  • Does the security network need to be completely isolated?
  • Will the backbone support fiber strands for non-Ethernet networks?

With all the fiber strands allocated, a growth factor should be considered. This will take into account the unanticipated network links that need to be established after the initial installation or the occasional backup fiber that is required due to damage of a fiber connector. Fifty-percent growth is considered a reasonable amount, but this will highly depend on the systems being supported and the growth forecast for the network. For example, on a research or computing campus, it may be prudent to have more vacant pathways for future cables than oversizing the fiber-optic cable on the initial install.

After factoring in the fiber growth strands to the initial requirement, a fiber-optic cable strand size can be selected. Most manufacturers have standardized on similar strand count sizes for their cables. For strand counts less than 12, the standard sizes are 1, 2, 4, and 6. For strand counts between 12 and 144, the standard strand counts are 12, 24, 36, 48, 72, 96, and 144. A 288-strand fiber is a standard size, but after that it is best to talk directly with the fiber-optic cable manufacturer to see what other strand counts are standard for them.

Optical cable types

With the fiber type selected, the ICT engineer will determine the cable type for each cable segment. Whereas the fiber type defines the optical performance of the fiber-optic glass, the cable type defines the materials protecting the fiber strands. For the fiber cable on a campus or building, there are two major groupings of cable: outside plant and indoor.

Outside plant cable is intended to be routed outdoors. It may be designed to be directly buried in the ground, installed in conduit, in an innerduct, or supported between utility poles. The layers of the cable jacket are designed to protect the fiber-optic strands from the harsh outside environment of extreme cold and heat. It can protect the fiber from water intrusion where the cable is routed through a manhole that is flooded with water, and it can incorporate an armor to protect against rodents. Outside plant cable is constructed to survive outdoors, but this results in a combination of materials that don’t allow it to pass smoke and flame tests for indoor installations.

NFPA 70: National Electrical Code (NEC) identifies the parameters that have to be met for indoor-rated cable. Cables that do not meet the NEC’s listing are considered “unlisted” cables and are limited to not entering a building 50 ft past the entry point. A few manufacturers are making outside plant cable that also meets NEC listing requirements to route indoors. The cable uses slightly different material and a water-blocking tape instead of the water-blocking gel. For cables crossing a campus and entering a building, the preference is to stay with one continuous segment of cable from communication room to communication room. Adding a fiber-optic splice to extend the cable past 50 ft is expensive and adds attenuation to the fiber link.

Figure 3: This image shows an armored fiber-optic cable for indoor use. Courtesy: Panduit Corp.

Table 2 provides a summary of the indoor fiber listing types from tables 770.154(b) and 770.179 in the NEC. A fiber-optic cable has to have one of these markings on the cable from the manufacturer to be considered a listed cable per the NEC. Furthermore, a cable has to be made of material suitable for the environment. Only a cable with a “plenum” rating can be installed in a plenum environment as described in NEC paragraph 300.22. Cables installed in an area defined as a building “riser,” such as a vertical shaft, at minimum require a riser rating. General-purpose cables can be installed in a building in areas that are not considered plenums or risers. Table 2 also identifies which cable types can be substituted for another. Generally, a cable that meets a more restrictive smoke and flame rating, such as a plenum-rated cable, can be substituted for cables more suitable for a less-restrictive environment.

For many years, a non-conductive fiber-optic cable has been the preferred construction over a conductive cable. A fiber-optic cable is considered conductive if any of the cabling elements are metal. A non-conductive cable costs less, is lighter and smaller in diameter, and does not require bonding of the metal components to the building ground system. However, the trend over the last few years is to install an armored cable as shown in Figure 3 instead of installing the cable in innerduct. When placing multiple cables in a large conduit or cable tray, the innerduct provides added protection to the fiber-optic cable to prevent it from getting crushed, pinched, or burned through by the over-pulling of an adjacent cable. The armored cable can mitigate these hazards. Another benefit is that the armored cable has a smaller overall diameter than a fiber cable in innerduct. The armored cable takes less space in a conduit or cable tray. It also can reduce the cost of labor to install because the armored cable gets pulled in once, whereas using fiber in innerduct typically requires separate placement of the innerduct and then the fiber cable. There are manufacturers who make a fiber cable already installed in the innerduct, but this is more common for an outside plant installation than an indoor installation.

Another alternative to non-conductive fiber-optic cable is a “blown-in” fiber cable. In this type of installation, small ducts (8 mm in diameter) are bundled together under a common cable jacket (see Figure 4). The fiber cable is manufactured in small bundles of multiple fiber strands. With the use of compressed air or nitrogen, the fiber bundle is semi-suspended in a tube and pushed in until it comes out the other end of the tube. Installing a 11/4-in. multitube cable requires no more labor than installing a traditional innerduct of the same diameter.

Figure 4: A microduct is used for a blown-fiber installation. Courtesy: Duraline Corp.

The benefit is the multitube cable has seven pathways whereas the traditional innerduct only has one pathway. Fiber bundles can be blown in the tubes at any time. The unused tubes are sealed to avoid contamination while empty. Blowing in the fiber is significantly less labor-intensive than pulling cable through innerduct. It is just as easy to remove a blown fiber cable if it is later determined the cable needs to be replaced with a higher strand-count cable or a different mix of fiber-strand types.

Another advantage of this type of cable system is multiple segments of tubes can be connected with tube couplers, allowing continuous cable segments to be blown in more than 2,000 ft in length. This can be a significant labor-savings advantage over traditionally installed cable. Blown fiber would be ideal for outside plant installations where it would not be necessary to open every manhole to blow in a new fiber bundle, or in high-bay large buildings, such as a warehouse or in manufacturing, where getting to the cable pull points can be difficult. The multitube cable can cost more at the initial build-out because you are paying for all the unused vacant tubes. The ICT engineer and building owner needs to perform a cost-benefit analysis for a particular building type to determine the best type of cable to use.

Optical fiber with power circuits

The NEC allows fiber-optic cables to be routed in the same cable trays and conduits as data-network cables (Class 2 or 3 circuits) as defined in Article 725 or telephone-type communication cables defined in Article 800. The code is very clear that data and communication circuits cannot be routed with any type of power circuits. However, the code does allow fiber-optic cables to be installed with power circuits under certain conditions. This is addressed in NEC paragraphs 770.133 and 770.110 (B). When fiber-optic cable is routed with power, the power has to be 1,000 V or less. This was increased in the NEC 2014 edition from 600 V in the NEC 2011 edition. The code provides an exception for the 1,000 V limit to be exceeded. It states, “In industrial establishments only, where conditions of maintenance and supervision ensure that only qualified persons service the installation, nonconductive optical-fiber cables shall be permitted with circuits exceeding 1,000 V.” There are two overall conditions that allow fiber-optic circuits to be with power. This is when the fiber-optic circuit is part of a composite power cable or when the fiber-optic cable is classified as non-conductive. For example, a cable with an OFN, OFNG, OFNR, or OFNP listing. The code does not allow for fiber-optic cable with conductive elements to be routed with power.

Figure 8: This example demonstrates when the NFPA 70: National Electrical Code (NEC) allows a composite fiber and power cable to be routed together in the same cable tray and to the same panel. Courtesy: CH2MFigures 8 and 9 illustrate the conditions when fiber-optic cable can be routed with power. Rarely would you see this condition occur for an enterprise network. This would more likely occur for a SCADA or automation-systems circuit. Although the code identifies a composite cable connected to a panel with power, this is not necessarily a “power panel” as we would think with circuit breakers or fuses. The code is interpreting any panel with power above of a Class 2, 3, or communications circuit as having power such as a control panel, a lighting panel, or nonpower-limited fire alarm panel. The panel illustrated could be a PLC panel with exposed 120 Vac inside of it.

Figure 8 shows a tray divider where power and lighting cables are on the same side of a tray divider with a composite cable consisting of power conductors and optical fibers. The tray divider is intended to provide separation between the power-type circuits and power-limited circuits (Class 2 and 3) such as (LAN data circuits and communications circuits. Figure 9 shows a non-conductive fiber-optic cable permitted by the NEC to be routed with the power circuits. If the right side of the tray is intended for power-limited circuits, it would make sense to route the fiber on the right side where it is more likely to be accessed by personnel with power-limited cabling skills. Another consideration for safety is that even though the code has provisions for routing or terminating fiber-optic cable with power circuits, it is not an allowance that should be taken without concern for the technicians who will be installing the power and fiber cables. In the installer trade, there are those who are trained in safety and skills appropriate for dealing with power circuits and those appropriate for working with fiber-optic cable. It is rare to find someone trained for both. Those who work with fiber-optic cable in buildings tend to come from the power-limited trades that work with data and communication circuits. The safety concern would be that a fiber-optic technician entering a panel with power to repair or test a fiber-optic circuit would not understand the risk associated with exposure to power in the panel.

Figure 9: NEC allows non-conductive fiber cable to be routed with power conductors. Courtesy: CH2M

Looking ahead

The outlook for fiber optics as the backbone for building communications seems to keep expanding. There is no emerging technology intended to usurp its dominance. In the advancement of intelligent buildings, with the increase in data created by the Internet of Things, cloud data storage, and the proliferation of video, the need for the high-bandwidth capabilities of fiber-optic cable will only increase. In addition to fiber being used for data transport, fiber optics being used for building sensory systems will increase.

Currently, there are manufacturers that use fiber optics as a medium for intrusion detection. The technology detects minute mechanical waves that distort a light signal in the fiber. Through digital signal processing, this system can distinguish the difference in a signal between a person walking next to a railroad track and a passing locomotive where the fiber is placed next to a set of train tracks. This same technology could be adapted to other building sensory systems and possibly be one more signal to be carried on the backbone advancing buildings’ intelligence. The specialty fiber-optic systems leverage traditional communication technologies for optical glass and connectors, although the signaling is proprietary. As these new systems migrate into the building infrastructure, they will need to meet the same code requirements as conventional fiber-optic systems and may even integrate into the building network.

Definitions

CCTV: Closed-circuit TV

Cloud: A metaphor for network services and storage accessed through the Internet

DCS: Distributed control system

DDC: Direct digital control

EF: Entrance facility

ICT: Information and communications technology

IoT: Internet of Things; the network of physical objects or "things" embedded with electronics, software, sensors, and connectivity to enable devices to achieve greater value and service by exchanging data with the manufacturer, operator, and/or other connected devices.

IP: Internet protocol

ISP: Inside plant

LAN: Local area network

LASER: Light amplification by stimulated emission of radiation

LED: Light-emitting diode

LOMM: LASER-optimized multimode (fiber)

OSP: Outside plant

PBX: Private branch exchange

PLC: Programmable logic controller

PoE: Power over Ethernet

PON: Passive optical networking

RF: Radio frequency

SCADA: Supervisory control and data acquisition

TR: Telecom room

VCSEL: Vertical cavity surface-emitting laser

VLAN: Virtual local area network

VoIP: Voice over Internet Protocol


Timothy Kuhlman is an electrical engineer and telecommunications technologist at CH2M with 27 years of experience in the construction and design of structured cabling systems. James Godfrey is an automation technologist at CH2M with 16 years of experience with commercial and industrial facility controls systems design and commissioning. He holds an MS in electrical engineering.