Anthony Minichiello
Maximis Communication Consultants
When planning construction of a cable entrance facility (cef), there are many issues to keep in mind. For example, you must factor in the type of cable being used, necessary supporting structure, routing equipments, entrance into the building, and location of termination space.
Designing the cef also requires that adequate space be provided for current and future telecommunications cables, and it must provide safe conditions for cable pulling and splicing operations.
Four entrance methods are commonly used, and each comes with its own set of considerations:
•Underground: The support structure consists of underground plastic pipe (concrete encased) or steel pipe. Out-of-sight underground conduit provides mechanical protection of the cable facilities and reduces service interruption.
•Buried: This type usually is not recommended, unless the property owner or economic situation dictates. Incidents of dig-ups could create disruption of service. However, this installation is out of sight and so an alternative to conduit.
•Aerial: Usually runs from a pole at the property line to small buildings. Due to economics, soil conditions or other factors, attachment for this type of entrance is restricted by size of cable and span length.
•Air-to-air: This is a wireless alternative to other physical types of cefs. The device could be a dish or monopole, depending on transmission spectrum (microwave, satellite, cellular, or pcs media).
As with any job, cef construction must comply with standards set by the National Fire Protection Association (nfpa); Occupational Safety and Health Administration (osha); and National Electrical Manufacturers Association (nema). Also, any local or state regulations more restrictive than these standards should take precedence.
Here are some basic rules to ensure worker safety:
•Work clearances: Work should be positioned between workers` elbows and shoulders. Adequate means must be provided for optimum performance with adjustable platforms or scaffolds.
•Overhead: The recommended clearance is 32 inches between the centerline of the splice opening and the nearest overhead obstruction for a hard hat or free movement during work operations.
•Horizontal: The lowest recommended horizontal splicing level is 25 inches above the floor.
•Vertical: The minimum separation between splice closures secured in the vertical is limited by the space required to position the cable and closures in the structure and supporting hardware.
•Work area dimensions: Aisle space should be large enough to provide passage with sufficient work area to satisfy human requirements and limitations of equipment and tools. Three feet is the minimum width recommended.
•Security measures: To prevent un- authorized entry and to protect workers in the cef area, planners need to provide for security measures, including illumination. A communications circuit should be installed to permit occupants of the cef to call for emergency assistance.
The primary ventilation requirement for a cef is a 20% oxygen level. This prevents condensation and the accumulation of hazardous or combustible gases. To prevent hazardous gases from entering conduits, all underground conduits should be routed through gas-venting chambers and plugged before they are terminated in the walls or floors.
Cables routed between the cef and the terminating frame can contribute to the spread of fire and smoke, so they must be jacketed in fire-resistant and low smoke-producing sheaths. Common-bonding the cable shields to the central-office principal via a low impedance path can minimize electrical hazards.
In a subsurface cef, underground cable can be pulled either from the first underground manhole or from the cef. Pulling the cable from the cef to the first manhole is preferred because the pulling line will be safely enclosed within the underground conduit when under maximum tension.
This article is reprinted from OSP Engineering & Construction, another Penn-Well publication.
Tony Minichiello is a principal of Maximis Communication Consultants, a Concord, NH-based implementor of total outside- and inside-plant telecommunications facilities.