Power-over-Ethernet (PoE) describes the power supply to your end devices via a network cable (also called LAN cable, CAT cable or patch cable) without the need for an additional power supply unit.


  • Most end devices are delivered without a power supply unit.

  • To put the end devices into operation, you either need an optional power supply unit or an infrastructure that offers PoE.

  • You definitely need network switches for PoE support.

  • When using expansion modules (add-on modules), the voltage via PoE may not be sufficient. In this case, use a suitable power supply unit or another PoE standard.

  • Only use power supplies recommended by the manufacturer.

Table of contents

  • Wiring and usage

  • Technology

  • CISCO end devices

  • Error: The expansion module does not work despite the correct standard

  • Other producers

Wiring and usage

The great advantage of using PoE is that you only have one cable that leads to the phone. This network cable leads directly from the telephone to a switch or ends in a wall socket. This saves you an additional power supply unit that supplies the phone with power.

In this way, you can also place a terminal device at those points where no 230V power connection is available.

PoE can also be used with other devices, e.g. webcams or WLAN access points.

A general comparison between the wiring of a telephone with and without PoE is shown in the following diagram:


There are different standards with different services for PoE.

The two most important are:

  • 802.3af (PoE): This standard is sufficient for many telephones. It offers less power, but PoE switches with this standard are often cheaper.

  • 802.3at (PoE +): This standard can transmit significantly more power and can therefore easily supply large telephones with color displays and expansion units. The corresponding switches are, however, significantly more expensive.

Before buying your infrastructure, please check which standard you need or whether you need to order a power supply unit.

Please also note that some manufacturers have developed their own "standards" for power supply via network cables. These technologies are often neither 802.3af nor 802.3at and are generally not compatible with devices from other manufacturers.

If you want to be on the safe side, take a look at the product description of the end devices and switches and compare the standards required.

CISCO end devices

The following table will help you with CISCO telephones, KEM denotes an expansion module with additional function keys:


PoE 802.3af

PoE+ 802.3at

CISCO power supply

8851 + KEM x 1




8851 + KEM x 2




8861 + KEM x 1




8861 + KEM x 2




8861 + KEM x 3




8865 + KEM x 1




8865 + KEM x 2




8865 + KEM x 3




* The quick charge function on the rear USB port of the 8861 does not work if more than one KEM is connected and the phone is supplied with 802.3at.

** The quick charge function on the rear USB port of the 8865 does not work if more than one KEM is connected and the phone is not connected to a CISCO Universal PoE (UPoE).

*** 8851 works with two KEMs and 802.3at only if the hardware has revision v08. The hardware version is on the back of the device.

The mentioned CISCO power supply can be found in our shop.

Error: The expansion module does not work despite the correct standard

If your extension unit does not work despite the correct PoE standard, please log into the web interface of your CISCO device and follow these steps:

  1. Login as admin. You can find the password in your Placetel customer account under Settings> Telephone security

  2. Click advanced in the upper right corner

  3. Click the Voice tab

  4. Stay in the System tab

  5. Change Power Settings> PoE Power Required> Maximum

  6. Click Submit All Changes

  7. The phone will reboot and the module should then work.

You can also include this setting in auto-provisioning using our custom parameters.

To do this, please set the PoE_Power_Required setting to maximum in the respective end device under User-defined. Please note that correct upper and lower case letters are important.

Attention: Do not define this value for all end devices! In certain constellations, the value maximum leads to errors. Use this setting only if the extension module is not running with the normal setting.

Auto-provision power supply for CISCO extension module

Other manufacturers

Please check the power requirements for all other end devices on the relevant manufacturer's website.

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