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Connected Lighting Systems
Efficiency Study — PoE Cable
Energy Losses, Part 1
November 2017
i
Connected Lighting Systems
Efficiency Study—
PoE Cable Energy Losses, Part 1
Prepared for:
Solid-State Lighting Program
Building Technologies Office
Energy Efficiency and Renewable Energy
U.S. Department of Energy
Prepared by:
Pacific Northwest National Laboratory
November 2017
Authors:
Jason Tuenge
Karsten Kelly
Michael Poplawski
ii
PNNL-27079
iii
Executive Summary
Power over Ethernet (PoE) technology offers the ability to provide both low-voltage direct-current (DC) power
and communication over a standard Ethernet cable—also referred to as a local area network (LAN) cable or
Category cable. Light-emitting diode (LED) technology has reduced the power required for lighting
applications, while advances in PoE standards and technology have yielded substantial increases in the amount
of power that can be delivered to a networked device over a single cable. As a result, PoE technology is
emerging in lighting and many other applications beyond its historical foothold in telephony and networking
equipment. Several major LED luminaire manufacturers have introduced PoE connected lighting systems in
recent years, making this a potentially disruptive technology.
PoE lighting systems can offer improved efficiency relative to traditional line voltage alternating current (AC)
systems, because AC-DC power conversion losses can be reduced if this work is consolidated among one or
more PoE switches, rather than being distributed among a greater number of smaller LED drivers. However,
this effect can be offset to some extent by increased losses associated with increased voltage drop in the low-
voltage Ethernet cabling. In fact, these losses could exceed 15% in poorly designed systems. Aspects of cable
design that can affect cable energy performance include wire gauge, Category (e.g., 5e), fire rating, and
shielding. Unfortunately, most cable manufacturers only state maximum DC resistance (DCR) or reference
standards that specify DCR limits; few publish nominal DCR values.
This report summarizes the results of an exploratory study investigating power losses in Ethernet cables used
between PoE switches and luminaires in PoE connected lighting systems. Testing was conducted at the Pacific
Northwest National Laboratory (PNNL) Connected Lighting Test Bed in September 2017. A test setup
comprising a PoE switch, a set of luminaires, and a reference meter was used to test nine cable models of
varying design. Power measurements for two widely differing cable lengths—one near 50 m and another near
0 m—were used to determine the portion of PoE switch output power dissipated by each cable model. The
results were analyzed to explore the impact of cable selection on PoE lighting system energy efficiency, as
well as the effectiveness of guidelines recently introduced by the American National Standards Institute
(ANSI) C137 Lighting Systems Committee.
The key study finding is that the guidance offered in ANSI C137.3-2017 does appear to be effective in limiting
cable energy losses to 5% in PoE lighting applications, provided that the average cable length on a project does
not exceed 50 m. Additional findings include the following:
• Cable losses were found to decrease with increasing conductor diameter (i.e., numerically smaller wire
gauge), as would be expected. No such trend was observed for cable Category, fire rating, or
manufacturer; however, considering the study limitations (e.g., the set of cables tested), this does not
mean these parameters do not affect cable losses.
• In addition to the nine unshielded cable models that were tested in this study, three other cable models
were acquired but later excluded from testing, due to compatibility issues. Because two of these were the
only shielded cables, the effect of shielding on cable energy losses was not evaluated in this study.
• Cable power loss can be accurately determined using values reported by the power sourcing equipment
(PSE) if the powered device (PD) input power does not vary with cable length. Notably, of the two
luminaires used as a lighting load in this study, one did not hold input power constant in this manner, and
neither model reported its own power use.
The following recommendations, stemming from the study findings, are offered to help streamline the
adoption of PoE technology in lighting applications:
• PoE lighting system designers should specify that minimum American Wire Gauge (AWG) must be per
ANSI C137.3 guidance, or specify minimum AWG directly if even lower losses are desired.
iv
• PoE lighting system designers/suppliers/installers should publish statistics on PoE cable lengths used for
each project (e.g., minimum, maximum, mean, median), along with information on each model used
(e.g., wire gauge, Category, fire rating, shielding).
• The Institute of Electrical and Electronics Engineers (IEEE) 802.3 standard requires that PSEs (i.e., PoE
switch ports) and PDs (e.g., lighting loads with RJ45 jacks) be compatible with all compliant cabling.
Manufacturers of PoE switches or PoE lighting loads that are not compliant with IEEE 802.3 should very
clearly state as much in datasheets and other product documentation, make no claims of IEEE PoE
compliance, and consider redesigning so these products can be certified compliant in the future. It is not
sufficient to only state compatibility in installation instructions, especially if such documentation is only
provided after products are received (i.e., after a system has been designed and products have been
ordered). To prevent damage and other issues that can arise from incompatibility, buyers and specifiers
should consider using products independently certified (e.g., by the Ethernet Alliance) as IEEE PoE
compliant.
• Manufacturers of Ethernet cables and connectors (RJ45 plugs) should publish lists of compatible cabling
products or parameters relevant to compatibility (e.g., tolerances for overall diameters of cable and
insulated conductors) in product documentation.
• Given the growth of high-power PoE applications, more Ethernet cable manufacturers should publish
rated DCR values specific to each product. Although these values would be expected to fall between
standard nominal and maximum values, knowledge of actual representative DCR values would enable
selection of cables that minimize energy losses.
• PoE switch manufacturers should state measurement accuracy for switch-reported PSE output power in
product documentation. In addition, PSE output voltage should be reported by the PoE switch.
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