PoE is not a new technology. Originally serving as the backbone for voice-over IP (VoIP) systems, this technology has grown to power other office systems. The range of PoE’s application continues to grow steadily due to its increasing power-carrying capacity. It was at 7 watts 17 years ago; today, it is at 60W. With its low power consumption, LED lighting technology has expanded the scope of applications for LV systems, including PoE.
The applicable certification standards followed the technology. The IEEE 802.3 series of standards originally limited the delivered power to only 15.4W; later, however, the limit was increased to 25.5W, then two additional power types were introduced: up to 55W (Type 3) and up to 90W-100W (Type 4).
CE Code 16-300 series
For this application, a power/data circuit is considered a pair of insulated conductors (often twisted) or a pair of conductors within a common cable assembly (marked as being suitable for the application) stretching from power sourcing equipment to a powered device. (This recognizes that more than one pair of conductors in parallel in one cable assembly may supply one powered device.)
Examples of these power/data cable applications include extra-low-voltage lighting systems, closed-circuit television systems (CCTV), wireless access points (WAPs), distributed antenna systems (DASs), and building automation systems (BASs). The typical example is 4-pair ethernet cable with 8P8C modular jacks/plugs (8 position-8 contact) connectors, typically rated 1.3A max. per conductor.
New Rule 16-320 explains the Class 2 power/data circuit shall be supplied from power sourcing equipment with an output limited to 100V•A and to 60Vdc.
Safety concerns arose regarding power/data cable bundling; because they now carry increased current and power, these cables experience greater heating. To address these concerns, new Rule 16-330 clarifies cable and conductor ampacity, and application of de-rating factors.
There are different requirements for Class 2 power/data cables marked with “-LP”, limited power-type cables and communication cables not marked with “-LP”, specified in Subrule (2) and (3), respectably. For communication cables marked with “-LP”, the maximum current that each insulated conductor is permitted to carry shall be limited to the current rating marked on the cable. For communication cables not marked with “-LP”, the ampacity of each conductor is specified in new Table 60.
Limited-power cables are suitable for carrying both power and data. Limited power cables are marked with the cable type designation, followed by “-LP” and “(x.x A)”, where x.x is the current rating in amperes of each conductor in that cable.
For example, a cable marked Type CMG-LP(0.5A), 23 AWG would be suitable to carry 0.5A per conductor, regardless of the number of cables in a bundle. Type CMG, 23 AWG in a 7-cable bundle could carry up to 1.2A per conductor (based on Table 60, 60°C rating).
Where communications equipment rated at 60W or less is powered by a communications cable having a minimum conductor size of 24 AWG, it shall not be required to comply with bundling requirements.
Where Class 2 power/data cables are installed in an ambient temperature exceeding 30°C, the correction factors of Table 5A shall apply.
One of the answers not provided in the new Rules is about approval requirements for products connected to the output of power sourcing equipment with an output limited to 100V•A and to 60Vdc (which exceeds Class 2 power supply limits). As always, remember to check with your local authority’s approval requirements.
* This article also appears in the October 2017 edition of Electrical Business Magazine. Check out our ARCHIVE page for back issues.