Tips for wiring next-gen devices

Remote powering applications utilise the copper balanced twisted-pair IT cabling infrastructure to deliver DC power to IP-enabled devices. The popularity of this technology and the interest in expanding its capabilities is staggering. This article details advantages of using shielded cabling systems for powering remote network devices.

In less than a decade, remote powering technology has revolutionised the look and feel of the IT world. Now, devices such as surveillance cameras, wireless access points, RFID readers, digital displays, IP phones and other equipment all share network bandwidth that was once exclusively allocated for computers. It is common knowledge that the networking of remotely powered devices for autonomous data transmission and collection is driving the need for larger data centre infrastructures and storage networks. However, many executives aren’t aware that remote power delivery produces temperature rise in cable bundles and electrical arcing damage to connector contacts. Heat rise within bundles has the potential to cause higher bit errors because insertion loss is directly proportionate to temperature. In extreme environments, temperature rise and contact arcing can cause irreversible damage to cable and connectors. Fortunately, the proper selection of network cabling can completely eliminate these risks.

Choosing qualified shielded category 6A and category 7A cabling systems provides the following advantages that ensure a ‘futureproof’ cabling infrastructure capable of supporting remote powering technology for a wide range of topologies and operating environments:

• Assurance that critical connecting hardware contact mating surfaces are not damaged when plugs and jacks are cycled under remote powering current loads.
• Higher maximum operating temperature for IEEE 802.3 Type 2 PoE Plus applications.
• Fully compliant transmission performance for a wider range of channel configurations in environments having an ambient temperature greater than 20°C.
• An option to support remote powering currents up to 600 mA applied to all four pairs and all networking applications up to and including 10GBase-T in 70°C environments over a full 4-connector, 100-metre channel topology.
• Reliable and thermally stable patching solutions for converged zone cabling connections (eg, device to horizontal connection point) in hot environments.

Protecting your connections

Telecommunications modular plug and jack contacts are carefully engineered and plated (typically with gold or palladium) to ensure a reliable, low-resistance mating surface. Today’s remote powering applications offer some protection to these critical connection points by ensuring that DC power is not applied over the structured cabling plant until a remotely powered device (PD) is sensed by the power sourcing equipment (PSE). Unfortunately, unless the PD is shut off beforehand, the PSE will not discontinue power delivery if the modular plug-jack connection is disengaged. This condition, commonly referred to as ‘unmating under load’, produces an arc as the applied current transitions from flowing through conductive metal to air before becoming an open circuit. While the current level associated with this arc poses no risk to humans, arcing creates an electrical breakdown of gases in the surrounding environment that results in corrosion and pitting damage on the plated contact surface at the arcing location.

While it’s important to remember that arcing, and subsequent contact surface damage, is unavoidable under certain mating and unmating conditions, contacts can be designed in such a way as to ensure that arcing will occur in the initial contact ‘wipe’ area and not affect mating integrity in the final seated contact position.

To ensure reliable performance and contact integrity, Siemon recommends that only connecting hardware that is independently certified for compliance to IEC-60512-99-001 be used to support remote powering applications. This standard was specifically developed to ensure reliable connections for remote powering applications deployed over balanced twisted pair cabling. It specifies the maximum allowable resistance change that mated connections can exhibit after being subjected to 100 insertion and removal cycles under a load condition of 55 VDC and 600 mA applied to each of the eight separate plug/outlet connections.

Keeping it cool

The standard ISO/IEC operating environment for structured cabling is -20 to 60°C. Compliance to industry standards ensures reliable, long-term mechanical and electrical operation of cables and connectors in environments within these temperature limits. Exceeding the specified operating range can result in degradation of the jacket materials and loss of mechanical integrity that may have an irreversible effect on transmission performance that is not covered by a manufacturer’s product warranty. Since deployment of certain remote powering applications can result in a temperature rise of up to 10°C within bundled cables, the typical rule of thumb is to not install minimally compliant cables in environments above 50°C.

This restriction can be problematic in regions such as the Northern Territory, the American southwest or the Middle East where temperatures in enclosed ceiling, plenum and riser shaft spaces can easily exceed 50°C. To overcome this obstacle, Siemon recommends the use of shielded category 6A and 7A cables that are qualified for mechanical reliability up to 75°C. Not only do these cables inherently exhibit superior heat dissipation, but they may be installed in high-temperature environments up to the maximum 60°C specified by TIA and ISO/IEC structured cabling standards without experiencing mechanical degradation caused by the combined effects of high-temperature environments and heat build-up inside cable bundles due to remote power delivery.

Maximising reach

Awareness of the amount of heat build-up inside the cable bundle due to remote power delivery is important because cable insertion loss increases (signals attenuate more) in proportion to temperature. The performance requirements specified in all industry standards are based on an operating temperature of 20°C. The temperature dependence of cables is recognised in cabling standards and both TIA and ISO specify an insertion loss de-rating factor for use in determining the maximum channel length at temperatures above 20°C. The temperature dependence is different for unshielded and shielded cables and the de-rating coefficient for UTP cable is actually three times greater than shielded cable above 40°C. For example, at 60°C, the standard-specified length reduction for category 6A UTP horizontal cables is 18 metres. In this case, the maximum permanent link length must be reduced from 90 metres to 72 metres to offset increased insertion loss due to temperature. For minimally compliant category 6A F/UTP horizontal cables, the length reduction is 7 metres at 60°C, which means reducing maximum link length from 90 metres to 83 metres. The key takeaway is that shielded cabling systems have more stable transmission performance at elevated temperatures and are best suited to support remote powering applications and installation in hot environments.

A better patching solution

While TIA and ISO/IEC temperature dependence characterisation focuses on the performance of solid conductor cables, it is well known that the stranded conductor cables used to construct patch cords exhibit significantly greater insertion loss rise due to elevated temperature than do solid conductor cables. To maximise flexibility and minimise disruptions when device moves, adds and changes are made, a zoned cabling solution is the topology of choice for the building automation systems (BAS) most likely to take advantage of remote powering solutions. However, most BAS horizontal connection points in a zoned topology are located in the ceiling or in plenum spaces where high temperatures are most likely to be encountered. Fortunately, the risk of performance degradation due to elevated temperatures in zone cabling environments can be mitigated by using solid conductor cords for equipment connections.

The future of remote powering applications

The advent of remote powering technology has significantly increased the number of networked devices, with surveillance cameras, IP phones and wireless access points driving the market for PoE chipsets today. As the PD market matures, new and emerging remote powering technology continues to evolve to support advanced applications, improved efficiency and increased power delivery. Power over HDBaseT, UPOE and the work of the IEEE 802.3 4-Pair Power over Ethernet Study Group formed to investigate more efficient power injection schemes are enabling remote powering applications that will support new families of devices, such as lighting fixtures, high-definition displays, digital signage and point-of-sale (POS) devices that can consume more than 30 W of power. All trends indicate that four-pair power delivery is the future of remote powering technology. Choosing connectors and cables that are specifically designed to handle remote powering current loads, associated heat build-up and contact arcing are important steps that can be taken to minimise the risk of component damage and transmission errors.

Conclusion

As the market for remotely powered IP devices grows and more advanced powering technology is developed, the ability of cables and connectors to operate in higher temperature environments and perform under DC load conditions will emerge as critical factors in the long-term reliability of cabling infrastructure used to support PoE and other low-voltage applications that deliver power over twisted pairs. Fortunately, cabling products designed to operate under demanding environmental and remote powering conditions are already available today.