Unraveling electrical integration

04/01/2009


Building equipment systems—typically electrical and mechanical systems—and telecommunications systems are critical parts of a building's functionality. These systems need to coexist and are a primary concern for engineers. They have separate requirements and separate purposes, but are integrated within the overall facility. So how can the disparate systems coexist and perform in tandem to make the overall building functional?

Electrical and mechanical equipment are required to support a telecommunications structured cabling infrastructure and network equipment. That infrastructure in turn supports communication transport systems such as voice, data, closed-caption TV, security, BAS, and lighting controls. Therefore, it's critical that the systems work together, particularly in telecommunications equipment rooms.

 

There are a number of factors that come into play for a well-coordinated design. Power and mechanical requirements, grounding electrical equipment, and bonding telecommunications equipment come to the table with their own set of issues. Looking at Figure 1, one can see that equipment size, location, clearances, and conduit or pipe routing all influence the location of equipment within the space. Add the possible application of National Electric Code (NEC) Article 645Information Technology Equipment, which sets some parameters for IT electrical infrastructure, and engineers have a tangled web to navigate. Examining how equipment and telecommunications systems are interrelated will provide for a better understanding of how to make them coexist and work together.

 

Equipment versus telecom rooms

In the telecommunications world, “equipment rooms” and “telecommunications rooms” are terms often used interchangeably, but they are quite different. In fact, facilities may have three different types of rooms in which engineers must focus: an entrance facility (EF), an equipment room (ER), and a telecommunications room (TR). Large buildings may have separate spaces for all three of these, while smaller facilities may combine them into a single room. The more common approach is the EF and ER in a single space, with TRs, as required, to support each floor. EF, ER, and TR are generic terms defined by ANSI/TIA/EIA 569-B Commercial Building Standard for Telecommunications Pathways and Spaces . Building owners may have their own names for these rooms, although functions stay the same.

 

An ER houses the telecommunications equipment with a main or intermediate cross-connect. Active equipment and distributed backbone cabling originates in the ER and serves an entire building. In some facilities, there may be a need for multiple ERs for redundancy or for tenants in a multitenant building. Pathways consist of cable trays, ladder racks, raised-access flooring (RAF), and strapping and hooking. In addition to voice and data networks, other low-voltage services may include community-access TV, fire alarm, BAS, and audio/visual equipment.

 

TRs, which generally support only one floor, provide access from the backbone to the horizontal workstation cabling, which serves the work-area outlet (WAO). Comprising telecommunications equipment, cable terminations, and cross-connect cabling, main components in this space include equipment cabinets and/or racks, passive components—patch panels, patch cables, connecting hardware—and active components—switches, hubs, routers—that are connected to the backbone infrastructure.

 

Typically, a building will have at least one TR per floor, but depending on the size of the building, there may be more. ANSI/TIA/EIA-569-B recommends multiple TRs for a usable floor space that exceeds 10,000 sq ft. Also, if the cabling from the horizontal cross-connect to the WAO exceeds 295 ft, additional TRs will be needed.

 

Within both ERs and TRs, telecommunications equipment must coexist with the supporting electrical and mechanical infrastructures. The key to making this successful is to first define the requirements and equipment that must share the space.

 

Coordinating requirements

The integration of support equipment for telecommunications spaces requires close attention to the interaction of the supporting power and cooling systems. Power systems can include panelboards, power distribution units (PDUs), remote power panels (RPPs), or UPS modules. Cooling systems can be as simple as a supply and return duct to a fan-coil unit or computer room air conditioning (CRAC) units.

 

Bringing all these pieces of equipment into a single space generally creates coordination issues that must be addressed upfront, during the design process. For example, electrical equipment has code required clearances where parts require access and maintenance, as identified in NEC 110.26. In order to design for the equipment requirements, the actual types of equipment that will be used should be determined.

 

Panelboards

Panelboards are the simplest consideration of electrical equipment. They provide electrical power to the equipment within the space and can be surface-mounted on the wall.

 

It is important to observe the required electrical clearances for the panelboard (as well as other electrical equipment). NEC 110.26(A)(1) requires working clearance of 3 to 4 ft, dependant on the access to live parts, grounded parts, and voltage. Since most panelboards will be 208 Y/120 V in an IT space, this clearance is typically 3 ft. NEC 110.26(A)(2) also requires a 30-in. width of working space (or the width of the equipment, whichever is greater).

 

The requirement most often missed is dedicated equipment space (NEC 110.26(F)). It states that the space equaling the width and depth of the equipment from the floor to a height of 6 ft above the unit must be clear of any work foreign to the electrical installation (see Figure 2). This means that only equipment dedicated to the electrical system can be installed in this area. As such, no cable tray, conduit, or other IT infrastructure or mechanical piping can be installed in this space.

 

Power distribution units

In a larger IT system, distribution commonly is achieved with PDUs. In the telecommunications world, a PDU is defined as a plug strip. These provide receptacles, a disconnect switch, and sometimes monitoring in a single device mounted within a cabinet or rack.

 

In the electrical world, PDUs combine a K-rated transformer to accommodate harmonic loads (typically K-20 when 100% of the loads are high harmonic), panelboards, surge suppression, power monitoring, and single-point grounding into a single enclosure. These can generally be located in the cabinet or rack line-up, or around the perimeter of the room.

 

These are of more concern when coordinating equipment because of the size of the units and code-required clearance. Typically, a PDU requires working clearance in front of the unit, as well as on one side or the back of the unit. This would be as required by code or the manufacturer, whichever is more stringent. Other working and equipment clearances are the same as for panelboards.

 

RPP and UPS

Another option to distribute power to the cabinets or racks is an RPP. In this design, the transformer is removed from the telecommunications space and located in an adjacent space. Panels are then placed in an equipment row or around the perimeter of the room. The space constraints of an RPP are less than the PDU because it doesn't have a transformer; the NEC code required clearances are the same. The designer must coordinate these panels with the telecommunications equipment.

 

A final consideration is a UPS system, which is installed to provide uninterrupted power to a critical load. There are three types of UPS: offline, line interactive, and online double-conversion. Typically, an online double-conversion unit is used to support telecommunications spaces. These units convert the incoming ac line voltage to dc, and charge the backup power sources, which typically are batteries. The batteries are typically two types: valve-regulated lead acid (VRLA) or flooded-cell (wet-cell) batteries.

 

While it is not advisable to put a UPS system and batteries in the telecommunications space, there are times when it is a necessary evil. When that happens, VRLA, or sealed, batteries should be used. This minimizes the potential for a spill and does not require any special maintenance or containment in the space. Also, the VRLA batteries will need to be replaced every five years or so. Because of this, there must be adequate space to allow for removal and replacement of the batteries. Other working clearances are as required in NEC 110.26 depending on access to live parts, grounded parts, and voltage

 

Mechanical compatibility

Mechanical cooling equipment to support an ER or TR should be at the same level of complexity and redundancy as the electrical design. For a small TR, a mechanical system could be as simple as a fan coil unit; a complex ER with rows of equipment cabinets and racks would need a CRAC unit.

 

A mechanical engineer needs to understand the kilowatt (kW) load that exists in the telecommunications spaces. This can then be converted to Btu/hr, which is used to properly size the mechanical equipment. Knowing the load that must be cooled and the redundancy of the system will determine how many and what size mechanical units are needed to cool the space.

 

Just as it is the case with electrical equipment, mechanical equipment needs proper maintenance clearances. The routing of any piping connection to the units also must be coordinated with the electrical clearances noted above and the telecommunications cabinets. Support piping or ductwork cannot infringe on any required access clearances for other equipment, yet at the same time must be accessible to allow for maintenance.

 

Bringing grounding and bonding together

The terms “grounding” and “bonding” often are used interchangeably; however, they are distinctly different. Grounding is the establishment of a reference for the electrical power source. Bonding is a connection to establish electrical continuity and conductivity. It is intended to equalize safely and effectively the potential differences between two metallic objects. It's important to note that the grounding electrode system, equipment grounding system, and bonding infrastructure for telecommunications have different purposes, but work together.

 

A grounding electrode system occurs at the electrical service entrance, establishing a zero-voltage reference for the electrical system and dissipating currents from lightning strikes. The electrical equipment grounding system provides a continuous fault current path to remove potentially dangerous voltage from equipment, as well as clear a fault by opening an upstream overcurrent protective device. Both the grounding electrode system and the equipment grounding system are required by NEC Article 250 and typically designed by the electrical engineer.

 

Designed to equalize potentials between objects during electrical fault conditions or lightning strikes, a bonding infrastructure for a telecommunications system typically consists of a telecommunications main grounding busbar (TMGB) and a telecommunications bonding backbone (TBB, see Figure 3). The busbar is bonded to the electrical service single-point ground, which is also where the connection to the grounding electrode system occurs. From this point downstream, the TBB is separate from the electrical bonding system and is intended to connect multiple TRs with a connection back to the TMGB and a single connection at the electrical service. It is tapped to a ground bus that should have an exothermic connection to steel and should also be referenced to the electrical equipment located in the space.

 

As a result, the TBB will equalize potentials between equipment in all telecommunications spaces. If multiple bonding connections for equipment are required, a ground bar should be provided. Also, it is important to size the all bonding conductors properly to limit the effect of the impedance on the system.

 

How NEC Article 645 works

One of the critical elements behind the design of equipment and telecommunications rooms is NEC Article 645, which provides installation guidelines for the electrical equipment in an information technology room. The main thing Article 645 does is to relax the IT room electrical wiring requirements found in Chapters 1 through 4 of the code. Any telecom space can have a requirement for Article 645 if the leniencies are being used. To use these leniencies, the NEC requires the following for each IT space:

 

  1. A way to disconnect power to electronic and HVAC systems serving the ER or TR.

  2. A separate HVAC system for the space, or fire/smoke dampers if the HVAC serves other areas.

  3. Listed IT equipment is installed, meaning it's a computer-based business with industrial-level equipment. This means that spaces with personal computers are exempt.

  4. The room is accessible only to support personnel.

  5. The room comprises fire-resistant rated walls, floors, and ceilings.

From an IT standpoint, the biggest concern for conformance is the disconnecting means of electrical and HVAC systems. Commonly, an emergency power off (EPO) button is used to de-energize everything in the room with a single push, meaning all the redundancies—UPS, generators, PDUs, CRACs—designed to keep this room online can be defeated in an instant. This device must be located at each of the principal exit doors from the space.

 

It is also important to note that equipment in these spaces that a user may not want to de-energize for other reasons also will be disconnected from its source. Common examples include security and life safety equipment. This should be taken into account when designing the space. Equipment also will need to be disconnected from any internal battery source if it exceeds 750 VA.

 

This failure can be avoided by designing the room to meet NEC Chapters 1-4. A common misunderstanding is that Article 645 is not required. If all the requirements of Chapters 1-4 are followed, Article 645 does not need to be applied to the space. Under these sections (Chapters 1-4), conduits and raceways need to be secured in place, cables and cords cannot pass through a grommet or tile opening in the RAF, and receptacles below the RAF cannot be used to permanently energize cabinet loads. If these rules are followed, it is possible to eliminate the single-point failure EPO. But, in doing so, there will be some loss of flexibility and the initial cost may be higher.

 

It is all too common to lose track of the fact that information transport systems aren't all that reside in telecommunications rooms. In order to make sure that the mechanical, electrical, and telecommunications equipment functions properly, coordination must start during the design phase, with interaction between all disciplines. Understanding the needs of other engineering disciplines will lead to a functionally sound, code-compliant space to support the facility for years to come.

 

Author Information

Lehmkuhl is a principal with the Applied Technology Group of RTKL, an architecture and engineering firm. With 12 years of electrical engineering experience, Lehmkuhl has been involved in designing electrical systems for government, corporate, and educational facilities.

Glossary of terms

Active electronics : Any component in an IT space that requires electrical power. Switches, hubs, and routers are examples of active electronics.

 

Backbone cabling : Telecommunications cabling (copper or fiber) that connects the TR and ER or EF.

 

Connecting hardwar e: A device used to connect cables.

 

Hub : A network device used as a centralized point to connect Ethernet devices together.

 

Horizontal distribution : Telecommunications cabling (copper or fiber) that connects the work area out to horizontal cross-connect in the TR.

 

Network switch : A hardware device that joins multiple computers or network devices within one local area network (LAN).

 

Passive equipment : Any component in an IT space that uses a mechanical connection and does not require electrical power. Patch panels, patch cables, and connecting hardware are examples of passive equipment.

 

Patch cables : A copper or fiber cable used to connect one device to another device to allow signal routing.

 

Patch panels : A panel allowing horizontal and backbone cable connections. This is typically located in a cabinet or rack.

 

Router : A network device, used to route or forward packets of information.

 

Work area outlets (WAO) : Outlet for connecting the tenant/user equipment (i.e., computer) to the network.

 



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