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Newbie to electricity here, quick question:

I want to run electric over existing LAN cable (not POE), which of the following is better or workable:

Scenario:

  • 5 CCTV cameras, each requires 9V DC 0.6A
  • LAN cable length varies from 5m to 20m, 26 AWG copper cladded aluminum cable for each pin (8 pin in each cable)

Method 1: 240V AC to 9V 10A DC power supply > cable > cameras

Method 2: 240V AC > cable > original AC-DC adapter > cameras

Shall I convert AC to DC before or after the cable? Will any of these method works? since the load is very small. It's almost impossible to run new cable, will my preferable method 2 works in this case?

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    \$\begingroup\$ When you say "LAN cable" do you mean CAT5 or or CAT6 or coax or even optical fibre or something else? Why are you not doing POE? That solution is off the shelf ready to go and provides enough power for what you need. \$\endgroup\$
    – Puffafish
    Oct 26, 2020 at 8:33
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    \$\begingroup\$ DO NOT RUN 240 VAC OVER ETHERNET CABLE! \$\endgroup\$
    – winny
    Oct 26, 2020 at 8:42
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    \$\begingroup\$ @Aaron yes. The intended amperage doesn't matter. This is about not killing people, nor starting fires, not about not making cables warm. \$\endgroup\$ Oct 26, 2020 at 9:08
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    \$\begingroup\$ @Aaron, the cable insulation is unlikely to be rated for mains. The connectors certainly aren't, don't have the safety clearance and most importantly anyone working on the system wouldn't expect mains on an Ethernet (capital 'E') cable. \$\endgroup\$
    – Transistor
    Oct 26, 2020 at 9:12
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    \$\begingroup\$ Does not matter, the voltage "alone" is way beyond the rating of any CAT5/6 cable and illegal in most parts of the world. \$\endgroup\$
    – winny
    Oct 26, 2020 at 9:24

1 Answer 1

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Stay (the hell) away from feeding 240 V into a Cat 6 Ethernet cable.

These cables aren't isolated for such voltages – it would definitely be liable to hurt someone, or jump through isolation and start a fire. And it would clearly be your fault then.

Really, PoE is what you want. It's literally designed to do what you need. Also "Cat 6, however […] not rated for PoE": Guess what, PoE will work nevertheless. How you could get the impression it's rated for 230 V instead is a bit confusing, but I think you'll understand that directly feeding in 230 V is not an option.

There's so-called PoE injectors (for single cables, that's a small device you hook into your Ethernet cable, but in your use case, you probably want to simply buy an Ethernet switch that integrates that) to get the power on the cable, and "PoE splitters" to get it out. Some of these allow you to set a desired output voltage (e.g. 9 V), for others you'll need another step-down converter to convert the variable voltage coming out of your splitter to 9 V.

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  • \$\begingroup\$ Thank you for all the information you gave me, I guess I will scrap all my idiotic ideas and call an electrician for the job. Thanks again, I have learnt a lesson here :) \$\endgroup\$
    – Aaron
    Oct 26, 2020 at 15:16
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    \$\begingroup\$ why an electrician? No need for one. You need a PoE injector and splitters. That's it. Things you buy and plug in, no need for an electrician. That electrician couldn't put 230 V over a Cat 6 cable either! \$\endgroup\$ Oct 26, 2020 at 16:08
  • \$\begingroup\$ Normally I would say the same thing. But I just now saw on ali 1:1 transformers which is the primary purpose of isolation. So why not to use them to transmit 240V with high frequency via isolation transformer? I just calculated 50ma can kill a person so to be reliable not to kill lets say 20ma is only 5W. Well not much. \$\endgroup\$ Dec 3, 2022 at 10:10
  • \$\begingroup\$ @user1325696 "Aliexpress is willing to sell me something in wild disregard of both, standards AND safety ATOP OF common sense" is really not an argument for something being feasible. I answered "why not 240V" in the answer: not isolated for that voltage. \$\endgroup\$ Dec 3, 2022 at 10:46

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