Carry power over CAT5

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  #1  
Old 11-17-08, 12:06 PM
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Carry power over CAT5

Contractors did not place an outlet in my closet where all the CAT5s meet, so I had to use my router in another room via couplers and splitters, but I would really like to move it into the closet.

I saw there are PoE (Power over Ethernet) adapters, but I didn't feel confident enough to buy and use one of those. Are they really safe? Since they all would be carrying 12v, is there still any danger of electrical fire? Even though contractors ran the wires, I swapped the RJ11 faceplates with RJ45s, so I am also a bit worried about shorting anything while sending power over those connections.

Example: Newegg.com - LINKSYS WAPPOE12 12 Volt Power Over Ethernet Adapter Kit - Wired Accessories
 
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Old 11-17-08, 11:37 PM
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Save youself the $38.99 and do it yourself.

Seriously, if you're good enough at wiring to change out the RJ11's for 45's, you're good enough to inject power into the unused pairs using the router's own power supply.

It's really easy to do. The standard is to use pins 4 & 5 for DC+ and 7 & 8 for DC-. Pins 4 & 5 are the blue. 7 & 8 are the brown.

The only caveats you have to address are:
-- The wiring has to be right. If the data works now, you know that those two pairs (green & orange) are not shorted. Check for shorts between all possibilities of the blue and brown pairs with an ohmmeter.
-- The router's power draw in milliamps or amps cannot exceed the ampacity of the wiring.

To answer your question: Yes, even low-voltage systems can start a fire if not properly designed. Post back with the router's milliamps, the distance of the Cat 5 run from the power to the router, and the gauge of the Cat 5 (usually 24). The DIY system you build will be safe.
 
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Old 11-18-08, 06:54 AM
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I don't have ohm meter, let me check my multimeter to see if it has any option to check ohm specifically.
Regarding the router, it is plain Linksys router. How do I check the router's miliamps? Would it be on the power adapter? I will check the other required information and post those.
 
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Old 11-18-08, 09:33 AM
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A multimeter set to ohms will work. Look on the router near where the power supply plugs in. There should be a label on it that tells you how much power it consumes.
 
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Old 11-18-08, 07:09 PM
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Router is 500mA (based on adapter's output number)
Distance is between 15 to 30 feet depending on which room I use for power source. Since they go through walls, it could be as long as 50 ft. Wiring is CAT5e, 24g.
The thing I am worried about is if they pinched anything during wiring which may not have effected the ethernet but may cause short if I run electricity over it.


My other option is to draw power from wall switch that is right next to the closet.

Actually I just noticed the wall panel is on the other side of the closet, maybe I can pay an electrician a few bucks to pull an outlet for me?
 
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Old 11-19-08, 04:12 AM
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You're good to go with 500 milliamps as long as there are no shorts in the lines.

On each wall jack, punch down a foot or so of white/blue, blue, white/brown, and brown wires. Strip the ends. Twist the blue wires together and twist the brown wires together.

Cut the power supply wire in the middle and strip each one. Set your multimeter to DC volts. Plug in the transformer being careful not to let the wires touch. Put the red meter lead on one wire and the black lead on the other. If it shows negative voltage, swap the leads. Note the voltage (it may be more than 12, but that's okay.) The wire that's touching the red lead is positive. Look carefully at the wires. One will either have a stripe on it or a slight ridge to identify it.

Back to the wall jacks: On the transformer side, connect the + to the blue and the - to the brown. Plug in the transformer and make sure you have the same voltage reading on the router jack's blue & brown as you had when you tested for polarity. (Remember, blue is positive.) This will tell you that you have no shorts or opens in the lines. Connect the same wires at the router's side. Plug it all in and you're done!
 
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Old 11-19-08, 08:40 AM
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Thanks Rick.
I may have to get a spare adapter in case something goes wring. I don't want to end up without a router.
Regarding the last stage, once I connect routers adapter to the wires on the wall jack near power source, do I plug it in and go to the other end (closet) and check for voltage there to see if the reading is same?

So pretty much we are using two wires combined to carry positive and two for negative, as I assume it might be overload to carry them on a single wire.

I also just realized, I would have to do the same thing for my DSL modem since they need to beconnected. DSL Modems generally have 1000mA, would that be a problem?
 
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Old 11-20-08, 04:13 AM
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Make sure the wires aren't shorted at the closet end before you plug it in at the power source. Then check for voltage at the closet.

You are using two sets of wires not only to increase ampacity, but also to conform to the standard.

24-gauge can handle 2.1 amps. Doubling up increases it to at least 4, so a combined 500ma router and 1,000ma modem (1.5 amps total) can be run over the same wires. However, both must be 12 volts, and both have to be powered from one power supply, preferrably a 2-amp.
 
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Old 11-20-08, 07:23 AM
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Would it be OK if I run power to the Modem using another line of Cat5 instead of getting another adapter that can feed both? I have RJ45 in every room. One room can feed the router, while the other for the modem.

Also for the power source end, would it be OK if I make a power plug out of RJ45, so I can plug RJ45 to wall plate, while the other end would be plugged to the wall, crimped or soldered to the power brick?
 
  #10  
Old 11-21-08, 03:58 AM
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That's a very good idea. That way you're not making any changes to the building wiring. Let me know how it turns out.
 
  #11  
Old 11-21-08, 07:27 AM
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I will try this as soon as I get my spare adapter. Thank you once again.
 
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