What Is Central Office Power Cable?

TelcoFlex and EcoSafe CO are UL-listed central power office cables for use in the telecoms industry. These single-core telecom power wires feature non-halogenated insulation that’s lead- and silicone-free and which significantly reduces the generation of toxic smoke and corrosive chemicals when exposed to fire. Central office power cables meet the requirements of the GR-347-CORE Telcordia standard and UL 44 standard for safety thermoset cables. The cables are moisture-resistant, fire retardant, and rated for 600 volts.

Central Office Power Cable Applications

Central office power cable primary applications include cable tray and raceway applications in high-integrity telecommunications and data centers. This includes supplying power to cellular wireless towers, telecommunication exchanges, data center wiring, and backup generators.

Construction of Central Office Power Cables

Depending on the specification, these cables have a single copper insulated conductor, a separator, and nonhalogen rubber insulation with or without a protective braid.


Conductors use ASTM B-33 stranded, tinned copper. Types L2 and L4 use Class I stranding, while Type L3 has Class B stranding. Cable sizes are from 14 American Wire Gauge (AWG) through to 750 MCM.


Cables have a Mylar paper separator that prevents insulation bunching and facilitates cable stripping.

Insulation and Jacket

The cables have a non-shrink, TelcoHyde insulation. The insulation has excellent fire-retardant properties and meets the requirements of the VW-1 and FT-4 flame tests. L3 and L4 cables have a natural cotton braid that's saturated with a flame retardant.

Differences Between L2, L3, and L4 Cables

The primary differences between the three types of cable are the cable lay method and whether the cables have a braid.

Class I wire stranding used in type L2 and L4 cables use a rope lay method where individual strands are initially bunched together and then wound helically. This style improves flexibility and cable strength. Class B wire stranding used for type L3 cable is conventional helical stranding around a central core. This arrangement is cheaper to produce, uses fewer and thicker wire strands, but isn't as flexible.

Types L3 and L4 cables have a cotton braid saturated with a flame retardant, which improves fire resistance and flame-retardant properties. Type L2 (TelcoFlex II and EcoSafe CO II) cables have no braid,

Fire-resistance Ratings

These cables pass the UL 1581 WV-1 vertical flame test and the Canadian Standards Association (CSA) FT4 vertical flame test. Both measure the length of char after exposure to a burner for a measured time. The CSA FT-4 flame test is more onerous than the WV-1 and UL 1685 vertical flame tests. These cables are typically stamped with RHH/LS to show they are high heat resistant.

Difference Between TelcoFlex, EcoSafe and EcoFlex Cables

TelcoFlex and TelcoHyde are trademarks of Southwire Cables, while the Prysmian Group manufactures EcoSafe CO cables. Type L2, L3, and L4 cables from these manufacturers have broadly similar characteristics except in terms of their National Electrical Code Rating.

TelcoFlex wire has a Rubber, High, Heat (RHH) rating that has a maximum temperature rating of 90 degrees Celsius in dry and damp locations. EcoSafe CO cables have a Rubber, High Heat, Wet (RHW-2) rating that permits use in dry and wet locations up to 90°C. Both cables have a CSA Appliance Wiring Material rating of 105°C for dry locations. 

EcoFlex wire is an environmentally friendly cable that meets RoHs and WEEE standards for the elimination of hazardous substances and recyclability. Containing no heavy metals, phthalates or halogens, this cable is 100% recyclable. It’s also up to 32% smaller and 55% lighter than other comparable cables.