Building Code Compliance - wire management systems

Code Compliance

(Reprinted with the permission of John L Lebduska, Architect.)

In today's world, PLEC systems (Power, Lighting, Electronic and Communications) are essential in any commercial building. Every building's design team and owner/manager know that a building must be "electronically modern" to meet the demands of an increasingly communications-driven world. Not just office buildings, but libraries, schools, science buildings, hospitals and entertainment buildings must have flexible wire management systems that can accommodate new equipment demands.

Fire prevention, in terms of wire management, is fairly simple. We must comply with both the intent and the writing of all applicable building codes. Building codes are, in fact, a "record of mistakes" not to be repeated.

Most codes have two aspects - the rules that are there to save lives and the rules that are there to protect property. Proper selection of the correct wire management/wire distribution systems can achieve both.

The true costs of failing to invest in proper life safety measures include:

Loss of life
Injuries to occupants and firefighters
Replacement costs
Lost revenues, rents and business
Higher cost of insurance
Lost tax revenue
Increase in fire fighting and police costs
Impact on neighborhood property values and quality of life
Loss of jobs
Diminished value of asset

Therefore, when we evaluate and select any system, every aspect that affects people's safety must be considered. It is a prudent investment in the welfare of the community. In addition, safe buildings are more marketable and retain their value better.

Let's begin with the fact that all available systems can be designed properly and can be safe and code compliant. There is no "perfect system" that answers every building's requirements and often, combinations of systems are necessary to address user needs.

The purpose of this analysis is to make architects, engineers, owners, investors and agency heads aware of critical design issues. We will discuss each system as it relates to new construction as well as the renovation of existing buildings. We will touch on advantages, limitations and construction realities.

Our emphasis will be on prevention, first of ignition, then of limiting the transmission of smoke and fire. Our next goal will be to limit problems during construction and tenant changes to reduce hidden costs and maintain code compliance. In an article in Architectural Record (March 1998), Scott G. Nacheman, a firefighter and fire investigator, stated, "Even more important is fire suppression in void space such as ceilings, plenums, large wall cavities and raised floor systems." This statement emphasizes the need to worry about the places you cannot see.

We will begin with some basic concepts about wire management systems and components.

All components must be tested and approved, and must have a good track record. Testing means that an accepted test method, usually ASTM or NFPA, has been utilized by a licensed laboratory that is acceptable to the state and local code officials where the component will be used. Laboratories which are acceptable everywhere in the U.S.A. are Underwriters Labs and NFPA.
The purpose of electrical conduit or electric metal raceway is:
1. To protect the enclosed wires and cables from mechanical injury and corrosion.
2. To provide a grounded metal enclosure for the wiring in order to avoid a shock hazard.
3. To provide a system ground path.
4. To protect surroundings against fire hazard as a result of overheating or arcing of enclosed conductors.
5. To support conductors, prevent sagging and thinning of ductile copper or aluminum which could increase resistance and cause overheating.
6. To prevent exposure of wire insulation to fire or elevated temperatures which could cause toxic fumes.
Metal electric raceways, conduits and fittings must be galvanized. Review the National Electrical Code and Underwriters Laboratories Standards for other criteria and restrictions.
All electrical equipment must be properly grounded per National Electrical Code and NFPA 70, Article 250.
Due to human ergonomic requirements for viewing computers, scanners, printers and fax machines, locally controlled task-lighting is a must, resulting in considerable energy savings, but also resulting in higher wiring costs and more room required for power wiring.
Costs vary greatly from one system to another. First costs, long term costs, risks and value engineering as an investment should be considered.

The systems that will be briefly considered and examined are:

Poke-Thru
Cellular Floor Systems
Wired Partitions and Power Poles
Access Flooring (raised flooring)
Flat Wire (under-carpet) System
Cable Tray Systems (ceiling based)

Poke-Thru Wiring
(For direct connect or for wired partition feed)

This system is one of the oldest wire distribution systems. Its advantages are: low initial cost, no additional floor-to-floor height and very little load added to the structure.

If building codes are a "record of our mistakes," Poke-Thru issues are well covered. Until the early 1970s, Poke-Thru's were not fire rated. The system requires core drilling through concrete slabs and/or steel deck, or placing rated sleeves in slabs. The wiring is in conduit in the ceiling below the floor requiring service, often in another tenant's space. This system has the highest likelihood of code violations.

Considerations

Core drilling is very messy. Dust, concrete debris, water and noise must be considered and most core drilling must be done "after hours" or on weekends.
In new buildings, architects/engineers can plan Poke-Thru locations and avoid unnecessary drilling if they have accurate tenant layouts. However, tenants will usually have workstation layouts that require drilling.
Structural damage to slabs can occur unless U.L. and local codes are followed stringently.
As much as 40% of the ceiling plenum is unavailable for Poke-Thru because of ductwork, piping and other obstructions.
Specifications for drilling should be established to avoid drilling through column reinforcing in slabs, buried pipe or conduit. Spacing of holes, maximum size and sleeve type should be specified.
Inspection and supervision are essential during and after the installation.
The New York City Code requires a Controlled Inspection Amendment to insure proper fire stopping.
Abandonment-approved fixtures are required.
Only U.L.-approved fixtures may be used.
"As built" drawings should be kept up to date to avoid the "Swiss Cheese" problem.
General restrictions of one outlet per 65 sq. ft. per beam span, with a minimum spacing of 2'-0" and a maximum hole size of 6" must be enforced. If not, the fire insurance policy may be void.
Placement of a Poke-Thru requires considerable coordination to avoid problems in the ceiling of tenant spaces below. The support T's, black iron and hangers must be dealt with when placing conduits, outlets, boxes and hangers for the system. In addition, there is often a maze of ductwork, light fixtures, wiring, sprinkler heads and pipe, smoke detectors, telephone lines and sometimes vacuum tubing for HVAC controls.
The need to inspect and replace any structural fireproofing damaged by installing conduit or the Poke-Thru fitting is essential. Alteration of a fire-rated assembly could void insurance coverage if a claim is filed.
"Churn rates" of the building are a major factor in selecting this system and its high activation costs. The higher the churn rate, the greater the life cycle costs of Poke-Thru will be.
PVC coated wire must not be used unless encased in metal conduit. Basic costs will vary with the location, building type, cost of drilling and the number of contractors familiar with the system. The following additional costs would be added: required supervision, insurance for tenant damage, maintaining as-built records and the cost of disruption.
Overhead work is difficult at best. Poke-Thru competes for space with all other ceiling-based building systems.

Cellular Floor Systems

These systems differ from other wire management systems in that they are often part of, and integrated into, the structure of the building. The cellular system is normally part of a "composite design," using steel deck, welded studs and electrical cells to form a complete structural/electrical system in one operation. This accounts for its low overall cost. The need to have independent cells for power, telephone, data and life-safety wiring (smoke detectors, fire alarm, emergency lighting and emergency generation) is a very important advantage of this system. The electrical systems have their own space - they do not share space with other ducts, pipes, lights, vents or sprinklers; therefore, wiring in cellular floor systems is not subject to abuse by other trades. Wire security, shielding and wire integrity are not compromised.

Considerations

Only companies with complete U.L. system approvals and NEC compliance, as well as a proven track record, should be considered.
Systems with "open top trenches" allow wire lay-in from the floor, a labor saving factor. Also, capacity vs. pull-thru feeders is greatly increased.
All cellular floor systems with preset outlet boxes and trench headers require spray fireproofing on the underside of the slabs. Therefore, lightweight concrete offers no cost advantage. Bar joists are not U.L. approved to support most conventional cellular floor systems.
Shallow cellular systems can be used for rehabbing existing buildings, if the structure can take the additional load. New fill materials, i.e., self-leveling gypsum that cures in one or two days and meets all fire requirements, may soon be available.
Wire capacity of cellular systems is a major consideration in today's electronic age. Three-inch deep cellular systems provide optimum wiring space and spanning capabilities, with activations as close as 2' X 2'.
Since the A.I.S.C. (American Institute of Steel Construction) Code requires a specific spacing for deck weld-down or shear studs (not to exceed 18"), cellular deck systems that exceed this dimension are in violation of requirements for composite members and structural engineers should examine this very carefully. Significant reductions in composite beam strength can occur if this spacing is exceeded, even by only a few inches.
If cells are adjacent and separated only by a vertical web member, possible cross-overs may occur at open butt joints in the deck, creating a serious safety hazard. Call separation is mandated by U.L. #209 and also by the NEC. Only systems that maintain cell separation with concrete across the joint should be considered. Currently, only 3" deep cellular systems can comply.
All outlet boxes should have proper grommets at the entry holes to avoid accidental stripping of wires and a potential hazard. (See U.L. 209 and NEC.) Inspect samples carefully for wire exposure to raw metal edges.
Cellular floor systems perform best when abandoned wire is removed from the system. Good wire management and good housekeeping are closely related.
Consideration should be given to the type of wire used. PVC coated wire is known to give off toxic smoke if exposed to fire. For example, the Port Authority of New York and New Jersey prohibits the use of PVC in the World Trade Center. If installed, removal by the tenant is required. However, PVC wire can be used in cellular systems in other buildings. Wire in cells is protected against temperatures over 265( F for up to three hours by underside fireproofing.
The cellular system is a totally grounded system since it is welded to the steel frame. The use of plastic covers on the floor outlets will eliminate static shock on hand contact -- an important consideration for office occupants.
Communication systems often require R.F. shielding and wire security that cellular systems provide.
Cellular floor systems provide the best overall benefits of any wiring distribution system, including low cost, flexibility, capacity and wire management, at a cost that is competitive with Poke-Thru wiring.

Wired Partitions and Power Poles

These systems may connect to electrical ducts or cable trays in the ceiling. Power Poles and pre-wire partitions must be U.L. approved.

Considerations

Power Poles are really vertical electrical conduit. They must be securely anchored at the top and bottom since they may be struck by furniture, cleaning machines and people.
Care must be taken to protect wires from sharp edges where wires enter and leave the poles. Proper grommets, careful placement of screws, boxes and outlets is required for a safe installation.
Building owners may want to inventory some extra poles, partitions and fittings for future use. Systems that can adapt other manufacturer fittings will protect against obsolescence.
Pre-wired partitions are heavy and require secure anchorage since they often support desktops, shelving, printers, etc. An owner will have to think carefully about being "locked in" to one manufacturer. Where will spare partitions be stored? Who will transport them and install them when needed?

Partitions are pre-finished, creating possible conflicts with tenants, interior designers, architects, etc. Furniture fitting systems may go out of style. Partitions with raceways cost about $2.00 more per sq. ft. of area serviced than non-raceway partitions.
Architects/engineers will have to be satisfied that all pre-wiring meets local codes and has been tested. Assemblies will have to meet building code fire requirements for flame spread and smoke development. Carpet used vertically burns much more rapidly than at floor level.
Grounding must be checked for compliance with all applicable codes.
Tenant changes will be very expensive and require careful coordination and longer construction time.
Pre-wired partitions are often in conflict with local union rules related to safety. Re-wiring at the job site is a rare occurrence, but should be investigated.
The use of power strips is restricting in most building code areas. Check the NEC and local codes for acceptability.

Access Flooring (raised flooring)

Access flooring itself is not a wire management system. It is a means of producing a concealed space in which wiring systems and sometimes air systems can be hidden, and it allows for the random placement of PLEC wiring. The access floor must take all typical floor loads including concentrated loads. The actual wiring may be enclosed in conduit or ducts or may be exposed. Plenum-rated wires will be required if air is supplied under the floor.

Considerations

The floor system must have been tested for:
1. Concentrated loads
2. Rolling loads
3. Uniformly distributed loads
4. Impact loads
The architect/engineer must evaluate the structural impact of the raised floor, possible zoning issues related to building height, additional construction and building maintenance costs. The system can weigh from 5.7# to 7.5# per sq. ft. If an office bay is 28 X 28, the additional load on an interior column per floor is 4464# to 5887#. In addition, columns will be heavier, cumulatively, increasing foundations. In buildings 20 to 40 stories high, this is a substantial cost.
If the floor is 8" high, approximately 1.5" to 2" is the floor panel, leaving 6" for wire, ducts, conduit, boxes, etc., adding 13'-3" to a 20-story building or 26'-6" to a 40-story building. Stairs, elevator shafts, piping, standpipes, etc., are lengthened accordingly and must be considered as "related costs."
Since the floor creates a concealed space, smoke and carbon dioxide detectors should be installed; and in large installations where air is distributed below the floor, fire suppression should be considered.
Architects/engineers must also consider the problems related to "sick building" syndrome. Although duct systems may be cleaned to correct some problems, cleaning of access floor spaces used as air plenum is very difficult.
Sometimes, painted stanchions must be scraped to bare metal to ensure proper grounding for electrical connections.
Special panels are required where penetrations occur or panels must be drilled and grommets placed per manufacturing specifications.
N.F.P.A. 75-1998 Edition "Standard for the Protection of Electronic Computer/Data Processing Equipment" should be carefully reviewed. It suggests that drainage of these areas should be considered. Tools must be visually available for fire fighters to access the concealed spaces.
Changes are complex due to penetrations, leveling the panels and the random wiring below the floor.
Access floor has a very important place in today's buildings, but should be used only in areas where very high density or volume of wiring is required. In combination with a good cellular floor system, it can answer most demands. Access floor is an $8.00 to $9.00 premium over Poke-Thru or cellular floor systems.
In alteration or renovation work, the following are a few items to consider:
1. Floor load impact on existing structures
2. Floor-to-floor height available
3. Changes in doors and frames
4. Effect on exit doors and stairs
5. Effect on elevator landings
6. Compliance with A.D.A. (Americans with Disabilities Act)

Flat Wire Systems ("Under-carpet Wiring)

These systems are used in existing buildings that have severe limitations on wire placement. These limitations may be due to structural concerns, strict lease provisions, historic preservation requirements or severe time constraints.

The system uses a flat wire with a total thickness of 0.31". The wire itself has a conductor of .009" which is PVC coated and has a polyester protective coating and a metal to prevent physical damage from above (NEC Type FCC).

Considerations

The conductors are usually equivalent to No. 12 AWG.
The tape used must be approved by the wire manufacturer to ensure compatibility with the wire insulation.
The wire should be made in factory-prepared, pre-measured lengths and have pin connectors or other special fittings installed since field cutting and installation is very difficult.
Cables must be compatible with the users' computers, equipment and their interfaces.
Transition from hard wire systems require special accessible boxes that are visible.
The system cannot be used under fixed walls.
Most codes require carpet squares over the wire as the floor finish. The carpet must be premium grade and lay flat without gluing. Since sheet goods cannot be used, the design choices are limited.
Low-tension wire may cross over power wire, but power wire must not cross over power wire.
Care must be taken that nails, screws or fastenings used to secure furniture or equipment does not penetrate the wire.
All boxes, plugs, switches and outlets are highly specialized fittings. Designers should evaluate samples of all fittings and transition boxes before using.

Cable Tray Systems

Actually, cable tray systems are only a "part" of a wire management system. They are run in ceilings or exposed in industrial buildings. The trays are often made with expanded metal bottoms. The cables in the tray must be "self-protected" for safety and meet the requirements of NEC Article 318. Cables such as MI, ALS, SE, and UF are often used.

Considerations

Cable trays are usually used in dry, non-hazardous, non-corrosive locations where the wire will not be subject to physical abuse.
Care must be taken in placing hanger supports. Proper spacing per manufacturing specification must be maintained.
Turns and bends must comply with the NEC code covering proper radii to be used with each cable size and type.
Wires in the tough are limited to 20 percent of cross-sectional area.
Cables must be properly fastened to the tray.

General References

N.F.P.A. Life Safety Code Handbook 1997
N.F.P.A. 75 Standard Protection of Electronic Computer Data Processing Equipment, 1995 edition
N.F.P.A. 251 or A.S.T.M.E.-814 "Methods for Fire Tests of Through Penetration Fire Stops"
U.L. Fire Resistance Directory
B.O.C.A. Building Code
National Electrical Code
New Your City Building Code
Mechanical and Electrical Equipment of Buildings, 7th & 8th editions, Stein & Reynolds
Electrical Systems for Architects 1995, Aly S. Dadras, N.C.A.R.B.
N.C.A.R.B. -- Professional Development Program "Fire Safety in Buildings," 1996