Join 3,572 readers in helping fund MetaFilter (Hide)


What are the range limits of Power over Ethernet?
August 23, 2014 7:05 AM   Subscribe

I want to install a security camera on a wall about 50m from my back door. I intend to use Power over Ethernet as a power source. I have no experience with PoE, and have some questions.

From the research I have done, I think the answers to the questions I have are all 'yes' but it would be useful to have that confirmed by someone with more knowledge:

- is 50-60 m within the maximum range of PoE?

- I already have CAT6 in the house and would like to be able to bring the signal from the camera back to the network equipment under my stairs, so there will be two lengths of cable involved - one inside the house, from the central location to the outside wall (about 10m) and one outside (about 50 m), connected via a standard RJ45 connector and socket. Am I right in thinking that this makes no difference?

- Can I send data and power over the same line? Is there anything that I need to when running the cable, wiring it up or selecting equipment (such as a PoE switch) to enable this?

If there are any other issues that I should be considering, please let me know.
posted by Grinder to Computers & Internet (6 answers total) 2 users marked this as a favorite
 
60m is within the range of PoE, which can usually run around 100m. There may be some loss at the your socket, depending on the design, but I doubt there would be enough to matter.

PoE is designed to provide both power and data over the same cable. Some PoE switches have power to specific ports, which are labeled on the switch, while others can provide power to any ports - it depends on the switch.

The big thing you should look at is the power requirement of your camera. Different PoE switches can provide different levels of power to each port or groups of ports (known as the "power budget"), so you'll want to make sure what your switch can provide is in line with what the camera needs.
posted by eschatfische at 7:16 AM on August 23


you'll probably want to buy a PoE injector, instead of a switch, unless you have multiple PoE devices. It will add power to a single ethernet run, and be cheaper.
posted by TheAdamist at 7:18 AM on August 23 [2 favorites]


PoE was designed to have the same range as Ethernet itself, which is 100 meters.
posted by zsazsa at 3:21 PM on August 23


TheAdamist has the right idea, and I'll also add that I've had great luck with super cheap random Chinese OEM brand injectors. Even some decent stuff ships with those(IE: unifi APs). You don't need a fancy one.
posted by emptythought at 8:44 PM on August 23


Unless you plan to put more PoE kit in, a PoE injector is definitely the way to go - significantly cheaper (and cooler and quieter). BTW, this is definitely a standard use for PoE, we use it this way for a bunch of onsite cameras, as well as phones and wifi points. Just confirming it is rated for 100m, same as cat5e/6 - and yes, you can send data and power over the same CAT5e/6 cable you normally use for just data. That's the purpose of PoE, to minimise cabling needs for low-power isolated equipment.

The only thing to check is what standard of PoE your camera uses, and make sure you supply the right one! IEEE 802.3af is the generic standard (48V DC, for 15W per device) and you'll likely want gigabit capability; TheAdamist's link is an example of that, and covers most PoE devices. There are many like it.

Some devices need IEEE 802.3at which goes up to 25W; and there are some that need custom proprietary injectors (usually because of particularly high power needs) so just be aware of that, really.

The injector could either go by your network kit and run power the whole way; or run just data the 10m to your socket, and use the injector there to add power for the outside run*. Either will work fine at that distance, whichever is more convenient for power sockets really.

* please use outdoor rated CAT5e or CAT6 for that bit!
posted by ArkhanJG at 1:26 AM on August 24


There are two main types of PoE, active and passive.
  1. Active PoE is standardized by the IEEE 802.3af (PoE) and 802.3at (PoE+ which provides more power). Active PoE requires negotiation between the device and the power source. Double check if this matters, but I am pretty sure this is supported to the supported length of cable for ethernet of the particular type (100Mbps or gigabit). Active PoE is mostly the domain of enterprise stuff. It's not generally inexpensive. In general[1] you can plug a non 802.3af/at PoE device in to network port that has power being provided to on that standard and all will be fine.
  2. Passive PoE is simplistic and simply uses a pair of the 8 wires in an ethernet cable for running power. How much power this can provide and how far the device can be from the power source varies wildly. There are some "standards" but they are by convention rather than formalized. It's generally bad (tm) to plug a device that is not expecting passive PoE in to a port that is powered as such. If you have a well designed network device, it might not fry the device, but it really shouldn't work.
Some examples;

Ubiquiti Networks makes network cameras (they are most famous for point to point wireless and event WiFi hardware). They use passive PoE, mostly at 24v. They have the Unifi Video Camera which needs power from a 24v passive injector. They make a variety of injectors for all the various voltages their devices have used over the years. They also make passive poe switches that are both a switch and a power source for devices connected. They also make wireless access points that are powered by PoE. The majority of them are powered with passive PoE, but they do make the Unifi AP-Pro which can work with either the Unifi PoE standard or the 802.3af one. As Ubiquiti is trying to sell in to enterprises, they know they need to have more their devices work with the 802.3af/ac standard as enterprises prefer that type of switch as they have more features and management capabilities. So they make an active to passive adapter to let you power their devices with 802.3af standard power sources.

Netgear makes some consumer friendly switches that provide 802.3af power (e.g. GS110TP). They also make the GS108T which is a switch that is powered from an 802.3af power source.[2]

And to answer your specific questions;

Under 100M is fine for 802.3af/at. Whether that is acceptable for your particular passive varies wildly.

PoE is all about having a single wire that carries both the data and the power. Although I have seen some implementations that use an ethernet cable for power alone (these are seriously unusual).

In theory you should not be using UTP (unshielded twisted pair, a more general name for what the vast majority of ethernet cables are made of) outside. Your should be using things like Ubiquti's ToughCable with proper grounding and such. [3]

If you can be more specific about what products you are looking to combine, I can likely be more specific in my answer. Feel free to memail me if you don't wish to have this knowledge be public (or don't think it contributes to making this a generally useful question for reference for people that find it on google).

[1] My understanding of the spec says that it should always be safe, but my experience from the real world says it is possible to fry devices if you willfully do non standard things.

[2] I LOVE these two switches. The rooms in my house generally have a single ethernet port. This lets me put a switch in each room, and not have to worry about getting power to those switches as they are all powered over ethernet from a single master switch in the closet with the majority of the network gear).

[3] I have no particular allegiance to Ubiquiti networks. I have purchased a decent amount of their stuff over the years and have always been happy with them. I have no experience with their ToughCable, it was merely the first example of something that met all the specs I would be looking for if I were running cable outside. All my outdoor work has been done on commercial buildings and I hired people to do the work and they brought cable of appropriate spec.
posted by fief at 8:12 PM on August 24


« Older I've applied to two jobs this ...   |  Should I move from the small c... Newer »

You are not logged in, either login or create an account to post comments