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Remote Power

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Issue: How to remotely power the 3Com NBX telephones that exceed the distance of the power adapter

From the Group: We have deployed several 3Com Ethernet Power Sources without any problems. The EPS makes the NBX business telephone system very reliable when installed with proper Uninterruptible Power Supplies (Battery Backup). This method below was used prior to the EPS solution being available. We encourage you to use the EPS and only adopt the method below when necessary and with qualified technicians. The investment in the EPS is worth more than the initial costs in terms of telephone system performance, service, user satisfaction, and Dealer sanity.

The NBX telephones can be remotely powered from the central location where the NBX chasis is located. The purpose in remotely powering the telephones is for:

  • mission critical telephones for operators, executives, security, etc
  • customer sites with poor power
  • revenue dependent operations (loss of answered calls = loss of revenue)

The standard for powering the telephones with un-used ethernet cable pairs is not yet adopted. 3Com offers the Ethernet Power Source (EPS), that will power the NBX telephones from the NBX chasis on un-used pairs on the ethernet cable. The EPS is available in either 12 or 24 port configurations. The EPS adds a cost of $76 - 90 per station port. The EPS only works with home run cable drops and cannot provide power to telephones connected to hubs and switches in remote closets or office areas. The ethernet cable must run between the faceplate and the patch panel located with the NBX chasis. The existing 3Com NBX Power Adapter (3C10125) is designed to provide remote power on very limited distances. This solution is an alternative to the EPS, power adapter, and or individual telephone set battery backup units.

The transformers shipped with the NBX telephones have long power cords. These were cut in half. The ends with the transformers are connected to power strips and plugged into the battey back up system (APC BP-1000). The other ends are connected to the signal cable (spliced end) and then plugged into the telephone set (female end). DO NOT use gel filled scotch-loks or beanies for the splice. Use an indoor beanie for the splice.

The type of signal wire is important for several reasons. We used a shielded wire to minimize noise. The cable is plenum rated so as to meet any fire codes (in this case- the ceiling wasn't plenum). The gauge is heavier for carrying power for greater distance. The conductors are one (1) pair, 18 AWG. The manufacturer of the wire is West Penn Wire .(1-800-245-4964), P/N 25293B, and product name is Plencom II.


  • Disadvantage- power cable requires Dealer to perform moves-adds-changes.
  • ALWAYS disconnect brick (transformer) from power before cutting brick attached to signal cable when moving telephone.
  • As of September 9, 2000 - furthest cable drop for signal (remote power) cable, 194 feet.
  • Bricks (transformers) retain nominal current in capacitor. Expect a few sparks when cutting brick attachment.
  • When installing, remember to label the signal cable at both ends and each brick (transformer) for future reference.
  • Use a volt meter or Fluke DVM to measure current at station end to ensure proper operation.
  • Match the color of each conductor to the solid or white striped conductor at each end to ensure proper polarity.
  • As of September 9, 2000 - NBX 100 chasis and 16 telephones powered on APC UPS BP-1000.
  • Disadvantage- appearance is okay for machine shop, factory, and similar environments, but questionable for many offices.
  • Advantage- low cost, improved system reliability, low-tech solution.
  • Disadvantage- other contracotrs come onto premises for other work and without thinking, cut the power drops.