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This document harmonizes voltage, current, power, and safety standards/precautions for near-end line-powering equipment operating at less than or equal to 200 Vdc to ground and far-end line-powered telecommunications equipment. It also addresses the calculation of voltage drop and power loss on the intervening pairs, interoperability between near-end and far-end line-power equipment from differing vendors, electrical protection and service continuity during low-level transient events caused by ac induction, and Ground Potential Rise (GPR). Line-powering voltages covered by this standard are Class A1, A2, and A3 as defined in GR-1089-CORE [21].

Background & Purpose

Line-powering (including express/span powering) is the use of the twisted pair copper plant (19-26 AWG) to pass dc power from a source in a building or cabinet to an outside plant remote cabinet/enclosure, or equipment located on or within another building. Telecommunications networks have a long history of using line-powering for various tasks, such as the coin return mechanism of payphones, T-1 repeater powering, High-bit-rate Digital Subscriber Line (HDSL) remote unit powering, Fiber-To-The-Curb (FTTC) powering, Digital Data Service (DDS), etc. Line-powering remains popular for existing and emerging technologies because it does not require placement of power company meters, rectifiers, and batteries at remote locations. Even though power is dissipated (I²R losses) in the transmission of line power, it is still often more cost effective for the relatively small wattage needs compared to placing ac power and associated power-conditioning equipment at the remote end.

Line-powering voltages commonly found in the industry and addressed by Telcordia NEBS document GR-1089- CORE [21], ITU-T recommendation K.50 [15], and UL/CSA Standards 60950-1 [23], 60950-21 [25], 62368-1 [11], and 62368-3 [12] are less than 200 V with respect to ground (e.g., nominal -48 Vdc, -130, -190, ±130, ±145, ±190, etc.).

Line-powering voltages are either positively ground-referenced, or bipolar center-tap ground-referenced (e.g., ±130, ±145, ±190 Vdc). Negative voltage on the energized conductor(s), such as a nominal -130 V system, limits corrosion (versus a negative ground-referenced system) of the copper pairs when water intrusion occurs in OSP cables.

In addition to the information on line-powering in the above-referenced documents, there are maximum power and current limits in the NEC® (National Electrical Code® and NEC® are registered trademarks of the National Fire Protection Association, Quincy, MA) [4], Canadian Electrical Code [8], and National Electrical Safety Code (NESC) [3]; maximum voltage, power, and current limits in ANSI/ATIS-0600337 [2]; and additional electrical protection information for line-powering schemes in ANSI/ATIS-0600332 [1]. These various standards define telecommunications line-powering voltage limits, power limits, and safety-related precautions. This document is an attempt to bring the requirements, standards, and precautions from all of these documents (and relevant information from a few other sources) into a single consistent source, as well as provide user guidance on the engineering and application of line-powered equipment and cable.

This standard is intended to define line-powering circuit characteristics (e.g., voltage windows, power maximums) going forward, rather than cover all of the legacy systems. This does not preclude the use of other voltages and systems, but allows for interoperability of systems designed to this document. This standard also addresses performance of line-powering systems in fault conditions and provides manufacturers, installers, and users of line power systems with a consistent fault condition testing and recording method. The fault current levels determined through this analysis can be compared to standards IEC 60479-1 [9], Effects of Current on Human Beings and Livestock, Part 1- General Aspects and IEC 60479-2 [10], Effects of Current on Human Beings and Livestock,