Saturday, January 23, 2010

Direct Burial Cable – FAQ

How do you size OSP conduit?

As a rule of thumb, make sure the diameter of your duct is at least 1.15 times greater than the diameter of your cable, or one-half trade size larger in diameter than the diameter of the cable you plan to install. When using pulling eyes, the diameter over the pulling eye becomes the most critical element to sizing conduit.

You can estimate the diameter over the pulling eye (de) to be: de < 1.1 x dc (dc equals the cable diameter). Keep in mind that multiple runs, grade changes and multiple bends can reduce the usable space.

ANSI/TIA/EIA-758, Customer-Owned Outside Plant Telecommunications Cabling Standard, requires the use of a minimum 4 inch conduit.

How do I determine the Sag and Tension Guideline for self-supporting cables?

When installing self-supporting copper cables, determine the storm loading district where the installation will take place. Storm Loading districts are defined in the National Electrical Safety Code® (NESC®) for the continental United States, but may be further defined by state and/or local codes and ordinances.

Once identified, the loading district along with the product / pair count and AWG can be used to access guidelines for span lengths, sag and tension data.

Can I install copper cables in an area where they will be exposed to chemicals?

Chemicals can degrade the cable jacket material, depending on both the jacket material and the chemical. Before choosing a cable with a standard jacket material in areas where chemicals are present, contact us at 888-797-3697 for alternative jacketing options that are resistant to the specific chemical(s) in question.

For example, a jacket made of PVDF (fluoropolymer) or nylon (polyamide) will impart specific resistance to a number of classes of chemical compounds compared to standard materials of which cables are typically made.

What are the low temperature properties of filled OSP copper cable?

The current designs and materials utilized in the manufacture of LS/Superior Essex filled OSP copper cables, including our OSP Broadband (Cat 5e, Cat 6) designs, are suitable for use at temperatures of -55° C.

Excellent cold temperature performance is often taken for granted by users of LS/Superior Essex cable products but it should not be overlooked if one is considering cable products from other manufacturers. Industry standards specify cold performance at -20° C, a temperature which is well above the low temperature in many parts of the Northern states and Canada. A failure of a cable that merely meets industry standards would manifest itself as a jacket/insulation crack or a voltage failure, both of which could result in service problems.

What (if anything) can I use to clean filling compound from the conductors when splicing your filled copper cables?

First, check the closure manufacturer’s instructions. It may not be necessary to remove the entire filling compound from the cable conductors. In these cases, the majority of the filling compound may be removed by wiping the conductors with a clean, soft, dry cloth. When desired, there are commercial cleansers available through local distributors that will remove the gel from the conductor insulation. It is important to choose a cleanser specifically formulated to be compatible with the polyolefin used in telecom cables. Avoid "general use" cleansers as they may contain chemicals that can cause degradation of the insulation.

What are the main causes of noise in OSP copper telecommunications cables?

This response addresses "noise" as indicated by test set measurements and primarily related to power influence. Keep in mind that moisture or water is absolutely the major cause of noise audible to the customer. Conductor deterioration from water in a cable, water on the faceplate of a terminal or condensation causing current flow between two splice connectors will cause noise. Water is public enemy number one when it comes to copper cables. That is why we go to the lengths that we do to fill, flood, encapsulate and generally seal the cables from water intrusion.

The primary cause of noise is proximity to electrical power cables. Proximity does not mean that the power and communications cables are touching. High voltage transmission lines can and do induce fields at great distances from their physical location. Transformers and some electrical equipment can generate "noise" in an improperly grounded cable. The electrical fields generated by these power cables induce unwanted harmonics into the cable that manifests itself in what is commonly referred to as "noise".

The metallic shield of a cable, when properly grounded at each end, effectively cancels the effect of the power induced noise. In conjunction with surge protection devices it helps to protect the cable, associated terminals and customer equipment from damage caused by voltage surges as would be caused by lightening.

Other sources of noise are loose conductor splice connectors, improperly terminated conductors, loose or improperly installed shield bond connectors, proximity to a radio station transmitter. By code, communication cables, power neutrals, and metallic water pipes should have a common ground potential when all are present in a residence or commercial building. This is a safety measure as well as a "noise" prevention issue.

I am splicing filled OSP copper cable, what do you recommend for cleaning the cable ends?

Removal of the filling compound can be achieved by simply wiping the conductors with a clean, soft cloth or paper towel. Suitable commercial cleansers are typically available from your local distributor. When choosing a commercial cleanser, care should be taken to insure that the cleanser is designed for use on telecom products. Other cleanser types may contain solvents which are not compatible with the cable insulation causing the insulation degradation.

What type of bonding clamps are typically used for grounding OSP cables?

The standard alligator-type bonding clamps are commonly referred to as cable bonding and grounding connectors or shield bond connectors. Throughout much of the telephone industry they are also called "B Bond Clamps" and are found in sizes 1, 2, or 3. They may be used for grounding both aerial and underground OSP cables and the clamp size is determined by the cable diameter. When selecting a shield bond connector the type of shield must be taken into consideration. There are three shield configurations currently being deployed.

Type one addresses the bare shield (aluminum, bronze, etc.) which is easily separated from the jacketing. With bare shield tapes, the shield bond connector attaches directly to the shielding without involvement of the jacket.

Type two addresses the coated shield which does not bond to the jacket. Designs which utilize coated shield tapes which do not bond to the jacket can be treated in a manner identical to the bare shield with one important consideration - the bond connector must have "prongs" which penetrate the coating and make contact with the underlying shield material.

Type three addresses the coated shield which "bonds" to the jacket. Designs which utilize coated shield tapes which "bond" to the jacket require a clamp which makes a sandwich of the jacket and coated shield. Clamps used for this design require prongs which penetrate the coating and attach securely. For these designs, there is no need to separate the shield from the jacket.

Manufacturer's of these clamps include 3M, Electric Motion, Preformed Line Products and Thomas and Betts, and most if not all can be used in all three of the circumstances described above. The clamps are available from your cable distributor.

Can I run copper OSP cable inside a building?

Outside plant cables are not rated for UL CMR or CMP listing and when used inside buildings the National Electrical Code* requires the cable be placed inside metal conduit (NEC article 800-50, exception 2). In addition to NEC regulations, special state, county and local building/fire codes may apply when engineering projects utilizing this type of cable.

The NEC allows OSP cable to be extended from the outside a maximum of 50 feet to allow a termination to be made.

What is the "temperature rating" of copper OSP Cables?

The accepted temperature rating for outdoor products of -20° C (-4° F) to 80° C (176° F). This range is based on the temperature at which physical performance testing is conducted. Bellcore, RUS (REA) and ICEA specifications require cable cold bend and cable impact testing to be conducted at -20° C. High temperature testing is conducted on filled cables at 80° C to evaluate the compound flow characteristics of the filling compound. Although aircore cables are not tested at 80° C, raw materials used in filled cables are similar, and in some cases, identical to those used in aircore cable designs.

What is the recommended minimum bend radii when installing copper OSP cabling?

The recommended minimum bend radii for corrugated single shield tape designs is 12 times the cable diameter.

The recommended minimum bend radii for corrugated dual shield tape designs is 15 times the cable diameter.

The recommended minimum bend radii for flat, single, shield tape designs is 15 times the cable diameter.

What is the "voltage rating" of copper OSP cabling?

OSP copper cables have a 300 volt working voltage capability when used in communication circuit applications.

Communications cables are not formally voltage rated or listed as such by any listing or testing organization. OSP designs are manufactured to industry specifications that require, without failure, voltage testing between conductors and between the conductors and shield. This information is included in the electrical specification portion of each products catalog sheet.

What is the life expectancy of traditional OSP copper cables?

Outside plant (OSP) copper cables are designed based on a life expectancy of 30 years. Raw materials and finished cables are tested using life-cycle test procedures. OSP cable designs are available with many shielding options to accommodate a variety of installation environments. Choosing the appropriate shielding system for your environment will provide the greatest chance for 30+ years of trouble free service.

What guidelines should be considered when placing an OSP copper cable underwater?

Standard gel-filled OSP copper cables are designed for water-prone areas, but for applications that require the cable to be under significant water pressure (e.g., ponds, lakes or rivers) we recommend additional mechanical protection for the cables. By specifying one or two additional steel shields along with an additional over-jacket, the cable can be used for water depths of 40 feet or more. LS/Superior Essex designates cables with this extra protection as "+M" (for one additional steel armor) or "+2M" (for two additional steel armors).

LS/Superior Essex also recommends that the span under water be no longer than one reel length so that the length of the cable under water does not require splices or a connection point close to the water edges.

Even with the added protection of additional steel armoring, caution must be taken during placement of the cable to protect it from external hazards such as rocks, boat anchors and boat propellers. This can be accomplished by placing the cable in a conduit. The added protection of steel armoring, plus a conduit, offers the maximum protection for short underwater crossings.

Any other question please let us know and a special thanks to LS/Superiour Essex for this great information.