Archive for the ‘FAQ’ Category

What is a POE endspan?

Tuesday, June 16th, 2009

A POE endspan device would be a device such as a POE enabled switch which is placed at one end of the network cable and injects the POE power onto the network cable.

As distinct from a midspan device, which sits at some point along the network cable and injects POE power.

What is a POE midspan hub?

Thursday, June 11th, 2009

POE midspan hubs

POE midspan hubs are simply devices for injecting Power Over Ethernet (POE) power onto a network data cable. Let’s break it down a little:

They’re called midspan devices quite simply because they sit (are installed) at some mid-point along the data network cable lenghth i.e. they do not need to be at the source end (typically the server room, network switch or router position), nor do they need to be at the device location. Typically the midspan will be positioned at some point along the network cable run which is convenient for access/installation; near to a mains socket to supply it with power; and within the normal distance limitation of within 100 metres of the device to be powered by the POE midspan.

Of course, this ‘mid’ point does not have to be in the middle of a network cable length, the midspan could in fact be sited right alongside your central point network switch!

A midspan performs the same function as a single port POE power injector (it injects power onto a data cable), it has simply become convention for multi-port devices to be called midspan hubs rather than multi-port injectors.

The term hub is used to simply reflect the meeting point of cables, potentially lots of cables going in and out of a hub device. Most POE hubs are simply pass-through devices where power is added to the network cable e.g. there will be a ‘Port 1 IN’ and a ‘Port 1 OUT’ – the network cable goes IN with no POE and comes OUT with POE added.

Hubs are available in 4,8,16,24, etc ported versions.

Be careful to ensure that your hub has enough power to supply the number of devices you might want to connect to it; some hubs have a total power budget others promise a certain wattage per port.

POE switches are available, but that’s another topic …

Do I need a power over ethernet splitter?

Wednesday, June 10th, 2009

imgp2734It’s a simple question, so let’s try to provide a simple answer:

Many network devices such as network cameras, VOIP phones and wireless access points are POE ready. This simply means that they have the circuitry built within them to accept power supplied to them via the data cable. Therefore, they can be supplied with both power and data via a single network cable.

However, this does not mean that because a device is not ‘POE enabled’ it cannot be supplied via the advantageous single cable POE method!

If you use Power Over Ethernet, then (at the device end) use a POE splitter to separate the power from the data and present them to the device in the normal way e.g. RJ45 plug for the data and typically a barrel plug for the power, then the device is unaware of the fact that POE was used to reach it!

Some pitfalls to beware of:

  • Check that the POE Injector & Splitter you are using can supply the load that your device presents
  • It is best to err on the side of caution and use POE Injectors and Splitters from the same manufacturer
  • Check the voltage that your device needs; splitters are available for 3.3V, 5V, 9V, 12V, etc.
  • Check the power connector needed for your device; barrel connectors come in many different inner & outer diameters, and occasionally the opposite polarity …

More detail on many of these factors to follow in later articles, but we said we’d try to keep this one a simple answer to a simple question …

Your comments, feedback, queries and elaboration are always welcome …

How does POE work?

Tuesday, June 9th, 2009

The following video screencast from GSPamerica provides a good introductory explanation to power over ethernet – it runs for a little under ten minutes, so grab yourself a cup of tea and sit back and learn …




Understanding POE (Power Over Ethernet) from Peter Brissette on Vimeo.

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