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Can I use CAT5 for running a 12V DC (Power over Ethernet) to connect to a surveillance camera 12V DC, 500mA? Answered

Hello,

I want to set up surveillance camera system in my house.  The house is already prewired with 2 cables (1 CAT5 & 1 Coax RG6) at each end (1 end at camera place and the other end at main box).   I also have a Power Suply box with out put of 12.3V DC and 5Amps.  I want to use Coax RG6 for Video transmission and CAT5 for Power transmission.  The distance to run cable from a surveillance camera to a main box is about 40feet - 50feet long.  I'm trying to use a CAT5 cable for 12V DC to run for my surveillance camera (12V DC 500mA), I use 2 pairs for positive (4 wires) & other 2 pairs (4 wires) for negative.  I wonder if I do this way, will it have any hazard at all?  Please advise!

Any advice/help is appreciate!

Best regards,
DP

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dafonso

Best Answer 8 years ago

CAT5 is rated at no more than 9.8 Ohms/100m, so there will come a distance where you'll get a good deal of loss on the wire and it won't work. Will it get hot? well, that comes down P=VI. Or in this case, P=I*R*R, or, taking it one step further, P= I * (.098)^2 for one meter of wire.

If it starts to get warm at .1 watt, then you would need to run 10.4A through it. You're probably safe.

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dknpdafonso

Answer 8 years ago

Hi Dafonso and Steveastrouk!  

Thank you for your answers.  First of all, there is a little typo in my question, a Power Supply box gets 12V DC & 5Amp (not 5mA as typo).

Secondly, I'm not good at physical math, so I don't know how to calculate the Ohm, Watts, Volt, or Amp to be the right number for my camera power wiring as I describe.  I use CAT5 cable to run just ONLY for power to camera, NOT using this Cat5 cable for BOTH video & camera  transmissions.  The RG6 coax cable is using for video transmission only.   The video signal come out is very good. 

When I use a small electrical tester to test the CAT5 cable end at the camera place, it shows 12.1V DC (it drop 0.2V compare to 12.3V at power suplly box).  About the Watts, I really don't know how calculate or test it.  So, I don't really sure what Steve said "there's no safety hazard"???  Do you mean my CAT5 used for power is in hazard/unsafe, by a long run??

Please advise!

Thanks,
DP

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dafonsodknp

Answer 8 years ago

Short answer: You're fine.

.2V drop on a 50 foot run tells me that the entire run is dissipating about 32 milliwatts in transmission loss (assuming about 1.25 ohms for 50 feet), which is .64 milliwats per foot... no chance of that spontaneously erupting into flames.

Don't worry about the power supply amp rating... that's what it should put out at a maximum.

Calculating watts is easy enough. P(watts) = V * I, so take the voltage and multiply by the current. Since I didn't know the current driectly, I figured it out by using Ohm's law: V=I * R. I knew the approximate resistance, and the voltage.

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hubaignet

3 years ago

Hi, Can I use 12V-2Amp to power my Surveillance camera about 100 meters through UTP Cat 6 Cable...? (+ connected with 2 core and - is connected with 2 core).

Regards.

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steveastrouk

8 years ago

No.....Not unless you were running a transformer and the line voltage was higher.

Steve

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Re-designsteveastrouk

Answer 8 years ago

I was under the impression that on a long run with thin wire resistance was less with ac than dc.  I guess I'll go back and read that section again.

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steveastroukRe-design

Answer 8 years ago

I think you're thinking of HIGH voltage power transmission.

Steve

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steveastrouk

8 years ago

That's what I said isn't it - apart from the AC bit.

Steve

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steveastrouk

8 years ago

Whenever I've run PoE, I've struggled to get good enough regulation at the camera to be stable - that means the volt drop in the wire is a PITA. I've ended up running 5..6V above the camera requirement, and put a little voltage regulator at the camera.

Try it, there's no safety hazard, but be prepared to be disappointed by the result.

Steve