October 2008

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Using Structured Cable Solutions For BAS
The largest opportunity to reduce capital costs of installation in building technology systems is the installation of the system’s cable and cable pathways.

  Jim Sinopoli
Jim Sinopoli PE, RCDD
Managing Principal,
Smart Buildings
Contributing Editor

Author "Smart Buildings"

“There seems to be some perverse human characteristic that likes to make easy things difficult.”
Warren Buffet

One of the underpinnings of smart building technology is squeezing inefficiencies out of the installation and operation of building systems. At the physical level this means addressing equipment rooms, cabling and cable pathways. In fact, the largest opportunity to reduce capital costs of installation in building technology systems is the installation of the system’s cable and cable pathways. The way to facilitate this is to use one cable contractor for the systems, use as much structured cable as possible, and consolidate cable pathways. As an example at Ave Maria University, Bryan Mehaffey, VP for System Engineering, estimates that $1.5 million or about 40% was saved by using one cabling contractor and avoiding unnecessary and redundant cabling.

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In the 1980s many data processing systems had proprietary cabling, that is, manufacturer specific cable for systems from IBM, DEC and Wang. Structured cable was designed to be independent and handle different applications such as voice and data, and equipment from different manufacturers. The Category 5 or 6 cables which we all are generally familiar with are the latest cables from a structured cable standard known as ANSI/TIA/EIA-568 A and B Commercial Building Telecommunications Cabling Standard.

As more and more building technology systems evolve to IP and Ethernet, such as video surveillance, access control and lighting, structured cabling is incorporated in the installation. However, one area in which structured cable has not been significantly utilized is building automation systems, thus limiting how far one could converge the cabling plant in a smart building. What follows are some approaches major cable manufacturers have taken regarding the use of structured cable or BAS systems.

Structured Cable for BAS
Pushed to the side and almost swept under the rug is a standard called ANSI/TIA/EIA-862 Building Automation Systems Cabling Standard for Commercial Buildings. This standard is similar to the structured cable standard for telecommunications. While it may be news to some, the standard was established in 2002 and is currently under revision. Systimax, (at the time a part of AT&T which also included the world renowned Bell Labs which supported AT&T’s product line) was instrumental in creating the standard. Bell Labs’ research produced thousands of innovations and inventions including the transistor, the laser, C-programming language, Unix, the first wireless LAN, the first 56k modem, and TDMA and CDMA digital cellular telephone technology. Systimax, a premier cable manufacturer, is now part of Commscope and an industry leader in the utilization of the BAS structured cable standard.

TIA/EIA StandardThese two standards, one for telecommunications and the other for building automation systems, allow for a fully converged cable infrastructure in smart building technology systems. Both the ANSI/TIA/EIA 568 and 862 standards require an open cable infrastructure that is independent of any products and vendors. The primary basis for both standards is the use of twisted pair copper and fiber optic cable. Both standards have similar design guidelines (i.e the 90 meter rule) and parameters for reliability, capacity and compatibility.

There are two minor differences between the BAS and telecommunications cabling standards. One is that the BAS standard refers to a “horizontal connection point (HCP)” which is similar to Telecom’s “consolidation points” or zone cabling. The second minor difference is the BAS Standard’s use of a “coverage area” as opposed to Telecom’s “work area”.

Using structured cable in a BAS environment is different than its use in a typical data network. The cable topology and the location of the end devices are different. More consideration has to be given to signal loss budgets, devices placed on a link or bus, and the cabling distances supported.

BAS devices are generally power limited. The current draw and line voltage delivered by the power supply for a BAS device usually limits the signal distance for devices. Typically, 24 AWG balanced twisted-pair cable has the capacity to handle 1 ampere (A) of current draw per conductor with a maximum of 3.3 A per 4-pair cable.

BAS Structured Cabling Topology

Some contractors think that the BAS devices require a larger gauge cable (18 AWG) than the smaller gauge cable of Category 5 or 6 structured cable (24 AWG). When you take a look at the electrical characteristics needed for the devices though, the larger diameter conductor cable is usually unnecessary. A typical category 5 cable has the capacity to handle 1 ampere (A) of current draw per conductor with a maximum of 3.3 A per 4-pair cable. If a 24 V BAS device requires 50 mA (0.05 A) of current to operate with an allowable voltage drop of 10%, the maximum circuit distance using Category 5 cable is around 840 feet. If a BAS device requires more current than can be delivered by structured cabling the device probably needs to be powered locally.

If you think that using structured cabling for BAS system will void warranties, think again. Catch up on your reading and take a look at the application guidelines for major manufacturers such as Carrier, Johnson Control, Siemens, Lonworks and others that were developed nine years ago.

Reliable Controls Co-Existence
Another approach to infrastructure convergence is to use different types of cable for BAS systems but to converge the cable pathways for BAS and telecommunications systems. This approach still allows for cost benefits by using one cabling contractor and efficiencies in consolidating cable pathways but slightly diminishes the economics and functionality of using a full structured cable deployment.

Panduit, another leading cabling manufacturer, has a BAS connector module that supports the typical low voltage and field bus networks used in BAS systems which can be used in standard IT patch panels and faceplates. This provides for BAS systems to utilize their own cable and cable termination types, allowing for similar pathways, equipment rooms and enclosures to be used for IT and BAS. In addition, Panduit provides zone enclosures, a network consolidation point similar to the Horizontal Connection Point in the ANSI/EIA/TIA 862 standard, which allows all cables to be managed and patched in a single enclosure.

With the financial metrics of the approach proven and the availability of products and solutions from major manufacturers in the marketplace one wonders why the approach is not the standard method of operation for building owners, architects, engineers and general contractors. The excuses are usually twofold:

For more information about evaluating, creating and deploying smart building solutions, hardware and software technology design or to schedule a Continuing Education program for your office write me at jsinopoli@smart-buildings.com.


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