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Focus on… Installation: Electrical considerations for Telecommunications

A coordinated plan that addresses system requirements and protects against electrical disturbances is a critical component in today's sophisticated telecommunications environment.A coordinated plan th...


November 1, 2001  


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A coordinated plan that addresses system requirements and protects against electrical disturbances is a critical component in today’s sophisticated telecommunications environment.

A coordinated plan that addresses system requirements and protects against electrical disturbances is a critical component in today’s sophisticated telecommunications environment.

Plain old telephone service (POTS) just doesn’t cut it in a high-speed digital world. The same can be said for plain old electrical service (POES). The electrical systems that were adequate in buildings constructed even just a few years ago were not designed to support sophisticated electronic equipment and integrated building systems.

The threats from electrical disturbances are greater than ever — and the costs are higher. One conservative estimate places the cost of damage to equipment and network downtime in excess of US$26 billion per year.

This means that telecommunications designers must take a proactive approach in coordinating a complete plan for protecting building systems and networks against electrical disturbances. This idea sometimes takes a back seat to other considerations, but BICSI TDM 9 states the case very clearly: “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.”

A COMPREHENSIVE APPROACH

Today, the electrical system must fully support voice/data/video (VDV) in a coordinated fashion because VDV is now on a par with the “big three” of building systems: mechanical, electrical and HVAC. Because these systems are interconnected and rely to a great degree on electronics, they will not function optimally — and may not function at all — with an inadequate POES that is prone to electrical disturbances.

Consider the various systems that make a typical building function:

Networks

Telephone riser

Fire alarm riser

Security riser

Building management system riser

Closed-circuit TV riser

Satellite TV riser

Power riser

These systems intermesh and interconnect. For example, the fire alarm control panel connects to the main power, the telephone system, elevator controls, door controls and other systems. Computer networks and building systems must be protected against electrical disturbances.

A LOOK AT DISTURBANCES

What are electrical disturbances? One popular image is of a bolt of lightning and a computer blowing up; another is a total blackout. While such events qualify as electrical disturbances, there is more to be concerned with. The vast majority of these disturbances are transients, surges, spikes and noise (please see Figure 1).

Surges result from a variety of causes inside and outside of a facility. External causes include lightning and power line switching. Internal surges are generated by equipment motors and office equipment such as copiers and printers. Studies show that 70 per cent of surges originate within a building. Catastrophic surges, such as lightning strikes, can cause immediate disruption of data and damage to sensitive equipment. Far more common is latent damage and gradual degradation of electronic equipment that results from the cumulative effect of smaller, internal surges.

Noise results from switches, tools and lighting, as well as from EMI/RFI and poor grounding techniques. Noise has the potential to disrupt data and cause latent damage to hardware.

Overvoltage can be caused by generator or utility faults, proximity to sub-stations and sudden load decreases. This condition, which lasts for more than half of a cycle, should not be confused with surges, which are measured in milliseconds. High voltage, sometimes called “swell,” can damage equipment.

Undervoltage occurs during heavy demand on utilities and when heavy loads are introduced. Low voltage, also known as “sag,” can result in equipment shutdown, overheating or failure.

Blackouts result from utility failure or circuit overload. Consequences of blackouts include loss of unsaved data and potential hardware and software damage.

The above disturbances are all characterized by their unpredictability. Another disturbance is harmonic distortion, which predictably develops as a result of non-linear loads, rectifier loads and switch mode power supplies. Harmonics can lead to overheating of neutrals and transformers, insulation breakdown and fire.

PROTECTING THE SYSTEM

A properly designed electrical system can withstand all threats — a POES cannot. 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. This approach separates the building into strategic zones and protects these zones with surge protection devices.

Zone 0 is the outside environment where power disturbances from lightning, radio frequency signals and utility faults originate. This zone is 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. 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 migrating onto critical branch circuits.

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

THE BASICS

There are three basics to achieving protection against electrical disturbances in a network environment: installing a surge protection device with a clamping level of 400V at the main service panel; accounting for a panel-mount surge protection device (330V clamping level) for each network; and recognizing that if one node on a network has a plug-in surge protection device, then all nodes must be 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 some, but not all network devices, leaves the door open for damage — even if there are surge protection devices at the main and sub-panels.

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 is 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 tries to equalize the voltage and the chip burns 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 lies in the confusion over 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, excluding a blackout — an SPS functions as a surge suppressor. If other network components are not protected, the SPS at the server can
create a damaging voltage potential difference.

Multiple building “campus” environments with copper network backbones have the additional consideration of resistive coupling. Networked buildings present the risk of a large voltage potential difference across the distance between buildings in the event of lightning. Fiber optic backbones are 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 do not guard against is blackouts, which constitute less than one percent of power problems. Isolation transformer, ferroresonant line conditioner and automatic voltage regulator are terms that are often mentioned in the field of power conditioning.

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. The main function of this device 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. This device provides regulation by “tapping” the output voltage up or down based on changes to the input voltage. Automatic voltage regulators usually contain devices for surge protection and noise filtering, but they do not provide any harmonic containment.

Like an automatic voltage regulator, a ferroresonant power conditioner provides voltage regulation, noise filtering and surge protection. This device also offers excellent harmonic containment by producing a finely tuned circuit that only resonates at a specified frequency, usually 60 Hz. Therefore, changes on the input are not reflected on the output, and vice versa. As a result of 60Hz resonance, only 60Hz is allowed to be deflected back on the building’s distribution system.

COORDINATION IS CRITICAL

As recently as 20 years ago, the typical desk had a phone serves 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 cannot function with yesterday’s electrical system.

A coordinated plan that addresses system requirements and protects against electrical disturbances is a critical component of telecommunications system design.

Dale Budenski is a trainer and specification consultant for The Wiremold Company of Hartford, CT. He has been certified by BICSI as a Registered Communications Distribution Designer (RCDD). Mr. Budenski is based in Metarie, LA.


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