Active v. Passive

Discussion in 'Main Forum' started by -FAQ-, Sep 19, 2017.

  1. -FAQ-

    -FAQ- Member

    1. What's the difference between active and passive PoE?

    2. What does it mean when a PoE device is "passive"?
  2. poeworld

    poeworld Administrator Staff Member

    1. Active means the Power Supplying Equipment (PSE) sends a short low voltage signal to your Power Device (PD) as soon as it is connected to determine how much power it needs, then this PSE sends only that power. The most common case for this is when you have a PoE port someone could plug a laptop into by accident. The laptop isn't PoE and could be damaged by it, so, if you have an active PSE, it won't send any power to the laptop accidentally connected to it. Passive sends PoE power all the time, which works great for most PoE specific applications like cameras, WiFi access points, or a port you know only PoE devices are attached to. Both work great for the right application.

    2. Passive means that the power is on all the time. An 802.3af switch keeps the power off until a compatible device is attached. A passive PoE injector or switch provides the voltage (usually 48 volts) all the time, so you should only plug in PoE capable devices.

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