Cisco Power Injector

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Cisco Power Injector

Postby farwest » Mon Nov 26, 2012 8:47 am

We have some long runs in one of older church buildings to setup the wireless. After coming out of the 881 would it be feasible to start with a power injector or put it down line 100 to 150 feet which then would run another 130 to 150 feet to a switch. Global Services feels like we are to far with the first run which is close to 300 feet. How would a power injector affect the line if a ward computer is hooked up from the switch that is be fed by a power injector? We have a building that is like a fortress that the wireless doesn't move very good. Also no access above the ceilings so everything runs down tunnels underneath the building which run parallel with the building which makes the runs long.

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Postby jdlessley » Mon Nov 26, 2012 1:44 pm

Only two pair of the four pair available in Ethernet cable are used for 10BASE-T and 100BASE-TX networking. A power injector utilizes one of those unused wire pairs for low voltage transmission. It is the presence of the switch along a powered run that you need to be concerned.

The switch may not be designed to handle the power input. You would have to check the specifications to see if it even mentions PoE input. Some consumer grade switches will use PoE to power the switch but do not have pass-through capability. The best choice to place a power injector for a WAP is after the switch. You can use the same power outlet used to power the switch for the power injector. But the power should be injected on the cable running from the switch to the WAP.
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Have you tried finding your answer on the Help Center page or the LDSTech wiki?

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Postby sammythesm » Tue Nov 27, 2012 7:16 am

The cisco documentation says that PoE can reach up to 100meters (328 feet).

I don't quite understand the question about PoE affecting the clerk computer. You would not place the PoE injector on the line that connected to any device other than the wireless access point (unless, as jdlessley points out, you have a PoE powered switch or something in between, but then you need another injector on the downstream side of that switch to power the AP.)

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Postby john84601 » Tue Nov 27, 2012 9:17 am

If I understand right... it sounds like your trying to use the PoE Injector as a makeshift media extender / repeater. I'm not sure it will do the job you want, but if you have an extra one you could try.

PoE devices do not send power down the wire all the time. They use a low voltage "signature detection" process when they detect a new connection. If the device does not respond, it doesn't crank up the power. In the corp environement, we plug in non PoE devices into PoE switches all the time. In fact PoE has almost become the norm for chassis style switches.

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