Keeping Up With the Evolution of Telecommunications Wiring

Everyone knows that plain old telephone service (POTS) is inadequate in a high-speed digital world. The same can be said for plain old electrical service (POES) that wasn't designed to support sophisticated electronic equipment and integrated building systems. A central electrical consideration for telecommunications is proactive coordination in order to maximize protection. Like POTS and POES, plain

Everyone knows that “plain old telephone service” (POTS) is inadequate in a high-speed digital world. The same can be said for “plain old electrical service” (POES) that wasn't designed to support sophisticated electronic equipment and integrated building systems. A central electrical consideration for telecommunications is proactive coordination in order to maximize protection. Like POTS and POES, “plain old cable management” (POCM) just doesn't cut it in today's building environment.

This means telecommunications and electrical system designers must coordinate a complete plan for protecting building systems and networks against electrical disturbances. This idea sometimes takes a back seat to other issues, but the BICSI Telecommunication Distribution Methods Manual, 10th Edition is clear:

“Before incorporating telecommunications into the construction plans, a telecommunications distribution designer must possess an essential awareness of the prospective client's communications needs and wants. The designer must carefully consider voice, data, and video communications; building automation systems; and electrical power into, out of, and within the property.”

Today, voice/data/video (V/D/V) is on par with the “big three” of building systems: mechanical, electrical, and HVAC. Consider the various systems that make a typical building function: data networks, telephone, fire alarm, security, building management systems, and closed circuit and satellite TV. Note that these systems interconnect. To cite one example, the fire alarm control panel connects to the main power, the telephone system, elevator controls, door controls, and other systems. Because these systems are interconnected and rely to a great degree on electronics, they won't function optimally — and may not function at all — without an adequate electrical system that's free of electrical disturbances.

The threats from electrical disturbances are no small matter. Unprotected data cabling can bring large ground fault potential differences right to computers and other mission-critical equipment, resulting in data corruption, burned-out interface cards, or extensive damage to motherboards. One conservative estimate places the cost of damage to equipment and network downtime in excess of $26 billion per year.

Protecting the electrical system. A properly designed electrical system can withstand all threats. A POES can't. A zoned, whole-building approach to power and data quality is a comprehensive, coordinated solution that protects an entire building from sources both outside and inside the workplace by separating it into strategic zones and protecting these zones with surge protection devices.

Zone 0 is the outside environment where power disturbances from lightning, radio frequency signals, and utility faults originate. It's out of the control of equipment located within a building.

Zone 1 is the main service entrance. Because incoming cables carry the most severe threats, surge protection devices must be installed on all service entrance cables. Metallic conductors, such as conduits and water pipes, should be connected to a common ground point, and all surge protection devices should be grounded to the same electrical ground.

Zone 2 represents distribution panels or sub-panels, where supplemental layers of protection address disturbance remnants from the protectors at the service entrance, as well as any power quality problems created within the facility. Surge protection devices provide bi-directional protection from internally generated surge activity that migrates onto critical branch circuits.

Zone 3 includes points-of-use or workstations, where each piece of equipment, such as a computer or fax machine, should have separate protection to safeguard against ground potential differences.

Follow these three basic rules to protect against electrical disturbances in a network environment:

  1. Install a surge protection device with a clamping level of 400V at the main service panel.

  2. Install a panel-mount surge protection device (330V clamping level) for each network.

  3. If one node on a network has a plug-in surge protection device, make sure all nodes are protected.

The device at the panel reduces potentially catastrophic surges as they enter the building. The panel-mount device further reduces the potential for damaging surges. But protecting only some network devices leaves the door open for damage, even if the main and sub-panels are equipped with surge protection devices.

When a surge reaches the protection device on a computer, it will be diverted to the computer's chassis ground. However, the network data line connects to a network interface card with an input chip that's referenced to the chassis ground. The result is a sizeable voltage potential difference between the chassis of the protected computer and the downstream, unprotected computer. The network interface card will try to equalize the voltage, and the chip will burn up. Placing surge protection devices on all computers in a network eliminates this problem by allowing the voltage potential difference to always remain at zero.

Similar issues can occur with surge protection at the server. The root of the problem is confusion about the difference between an uninterruptible power supply (UPS) and a stand-by power supply (SPS). A true UPS continually provides power to the protected equipment with no break in the supply of power. An SPS, on the other hand, provides power but with a very short delay, typically referred to as “transfer time.” Under normal power conditions — that is in the absence of a blackout — an SPS functions as a surge suppressor. And if other network components aren't protected, the SPS at the server can create a damaging voltage potential difference.

Multiple building campuses with copper network backbones require you to also consider resistive coupling. Networked buildings present the risk of a large voltage potential difference across the distance between buildings in the event of a lightning surge. Fiber optic backbones are, of course, not subject to this phenomenon.

Other protection devices. Power conditioners provide clean, stable, isolated power by eliminating the damaging effects of surges, noise, overvoltage, undervoltage, and harmonics. The only problem they don't guard against is blackouts, which constitute less than 1% of power problems. The terms “isolation transformer,” “ferroresonant line conditioner,” and “automatic voltage regulator” are frequently mentioned in the field of power conditioning. But it's important that you not confuse these devices with stand-alone protective devices.

An isolation transformer generally isolates the load on the secondary side from the source on the primary side in conjunction with an electrostatic shield between secondary and primary windings. Its main function is to suppress common mode noise on the secondary side of the transformer.

An automatic voltage regulator provides voltage regulation through tap-changing transformer technology. These devices provide regulation by “tapping” the output voltage up or down based on changes to the input voltage. They usually also contain devices for surge protection and noise filtering, but they don't provide any harmonic containment.

Like an automatic voltage regulator, a ferroresonant power conditioner provides voltage regulation, noise filtering, and surge protection. However, they also offer excellent harmonic containment by producing a finely tuned circuit, which only resonates at a specified frequency, usually 60 Hz. Therefore, changes on the input aren't reflected on the output, and vice versa. As a result of 60 Hz resonance, only 60 Hz may be deflected back on the building's distribution system. This inherent characteristic makes the ferroresonant transformer an excellent harmonic containment device.

As recently as 20 years ago, the typical desk had a phone served by POTS and a typewriter or calculator that plugged into a POES duplex receptacle. Today's desk looks a lot different, and today's telecommunications and integrated building systems can't function with yesterday's electrical system and an uncoordinated approach to cable management. A coordinated plan that addresses system requirements and protects against electrical disturbances is a critical component of telecommunications system design.

Budenski is a specification representative for The Wiremold Co., in Metairie, La.

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