FIVE THINGS YOU NEED TO KNOW ABOUT POE TESTING IN INTELLIGENT LIGHTING INSTALLATIONS

Power over Ethernet (PoE) now supports a whole host of building systems, including intelligent lighting installations. If you’re dealing with these, Dan Barrera

Director of Product Innovation at TREND Networks, discusses five things

These may include:

• Power sourcing equipment (PSE): The PSE is commonly a PoE enabled network switch. The PSE will have two important power ratings – the maximum port power (determined by IEEE standards) and total PoE output and input (maximum continuous power delivered through any combination of ports).

• Ethernet cabling: Ethernet cabling for PoE lighting typically carries ratings of Category (cat) 5e, 6 and 6A with a maximum permanently installed length of 90m. Some lighting systems allow daisy-chaining fixtures if no segment exceeds 90m and the total cable length is within the manufacturer’s limits. The total distance is a function of the cable’s DC resistance specification. Depending on the category and number of AWG conductors in its construction, cable supports maximum frequencies from 100MHz to 500MHz with data rates from 1 to 10Gb/s. As with any electrical cable, voltage drop is a function of cable resistance, length and the load applied.

• Powered Device (PD): Powered Devices are the electrical loads in a PoE system, such as lighting fixtures. A PD has a minimum amount of power required to operate, which is important when designing a system to ensure the PSE can supply enough power.

A PSE may not be able to deliver the maximum port power to all its ports at the same time, as the total output of the combined ports may exceed the maximum output of the PSE.

Fortunately, PSEs are intelligent and won’t enter overload conditions and cause damage. It delivers power on a first come, first served basis and, at maximum capacity, additional requests for power will not be granted. Installers should ensure that the number of fixtures and their total power demand will not exceed what a PSE is rated to deliver.

The IEEE PoE standards define how much power should be available to a device at the end of 100m (328ft) of installed cabling and patch cords for a given Class of PSE. Unlike a mains electrical system, a PSE will not energise the data cable unless power is requested from a PD. So, standard electrical testing tools cannot be used to test PoE systems. Instead, tools such as PoE Pro from TREND Networks are used. These determine the PSE power class and inform the user of the unloaded voltage, the voltage under load and the wattage available under full load, providing a clear PASS or FAIL indication. This allows users to easily test hundreds of cables, identifying any that don’t meet specification.

Testing the PoE infrastructure before installation ensures that the PSE and cabling meet the power demands of the lighting devices or PDs.

Should a circuit fail the PoE load test, the tester can determine the source of the failure. Common culprits are the PSE or the cabling between the PSE and the PD. The tester is connected to the PSE port with a patch cord to test maximum delivered power. A failed test means either the port or PSE switch is bad, the port is configured incorrectly, or the switch is over its total power budget.

If the PSE test passes it means the power loss in the cabling is more than expected, so the cable test function of the PoE tester can be used to check the length of the cable. If the cable is too long, increased resistance from the additional length may cause the reduction in power at the PD location. If the cable is too short, the cable’s own resistance may be exceeding the specifications for cat 5e cable.

Another issue is copper-clad aluminium (CCA) cable. This is constructed of aluminium conductors, then coated thinly with copper. CCA cable has higher resistance than solid copper cable and should not be used in PoE applications, but, as it is cheaper, it is sometimes used.

With PoE becoming more prevalent, increasingly businesses need to create detailed reports for customers. These help verify that on-site technicians have completed an installation correctly. While mistakes are inevitable, in the past these issues would only become evident much later. This would result in poor customer satisfaction and costly call-backs to site.

These advanced test reports also clearly demonstrate that the power received on a cable passes the IEEE 802.3 af/at/bt requirements and is sufficient to power the installed device.

PoE Pro is now available with Bluetooth which works with the new TREND AnyWARE Cloud app to easily provide advanced installation and certification reports. Once results are uploaded via the app to the TREND AnyWARE Cloud web-based test management system, high quality PDF reports can be generated, giving installers a strong advantage over competitors.

PoE Pro is available through Avoke.

TREND Networks, trend-networks.com

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