How to Test if Your Ethernet Cables Support PoE

Fluke’s Jim Davis shows how to test if your ethernet cables support PoE using a DSX CableAnalyzer

Steps to test if your ethernet cables support PoE

Step 1 – Perform Standard Cable Testing

The first thing you want to do to confirm your Ethernet cable is PoE ready is make sure your cable passes the TIA/ISO standard field testings. In this case, Jim Davis does have a passing cable. If a cable fails the these, it’s not likely to be able to support PoE or other Ethernet needs.

Step 2 – Test Cable Resistance

However, there is one important part to PoE needs that the TIA and ISO tests don’t cover: resistance. In order to support PoE, the cable must have proper resistance performance. As Ohm’s law states, the more resistance a cable has, the more voltage you have to put in to get the power you want out of a cable.

The reason for this is the field-testing specifications don’t require a resistance test. However, the Fluke Networks DSX CableAnalyzer Series cable testers can display resistance values if you click on the more information icon. The test doesn’t tell you if the cable would be able to support power over Ethernet, which is where the advanced “+PoE” test comes in.

When selecting a test limit, such as Cat5e, there is an extended (+PoE) test option. This test compares the values in the IEEE standards for what’s required to support PoE to the resistance values of the cable. In order to support PoE, the specific cable Jim is using must support about 21 ohms of resistance, so the cable being tested in this video has too much resistance to properly support a PoE installation.

The other values tested in this advanced test are resistance unbalance and pair to pair unbalance. Resistance unbalance is the difference in resistance between the two conductors in a cabling system. This matters because it’s important to have the right resistance on each leg, and a similar resistance on each leg of a pair, so you can be sure all four pairs have similar loop resistance values for power over Ethernet support.

The right tool for PoE testing

In order to run this advanced test and ensure your network is ready to support PoE, upgrade to the DSX CableAnalyzer™ Series Copper Cable Certifiers.

Keep Learning

• Upgrading to Four-Pair PoE

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