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Author Topic: Will this setup cause a fire?  (Read 3066 times)
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I want to run 120V AC through a CAT5 cable. smiley-eek One twisted pair will be hot, another twisted pair will be neutral. The cable may be 6ft to 100ft. At the end will be a 12V, 7A power supply. Will it all melt to the ground? If so, Why? I can already draw 12V, 7A DC through a 6ft length using one twisted pair just fine..
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Do a test with a 6' run, and if it survives, the longer runs may also survive.
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The question you should ask yourself is if you are willing to take the liability of possibly setting your house on fire or killing someone. The insulation on cat5 wire is not designed for these power levels.
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I want to run 120V AC through a CAT5 cable. smiley-eek One twisted pair will be hot, another twisted pair will be neutral. The cable may be 6ft to 100ft. At the end will be a 12V, 7A power supply. Will it all melt to the ground? If so, Why? I can already draw 12V, 7A DC through a 6ft length using one twisted pair just fine..

The question can't really be answered unless you say what current will be flowing in the wires. Then you would have to research the wire size of CAT 5 cable and see what current it can handle. Just because you say at one end will be a 7 A power supply doesn't say what current will really be drawn at the end. That's just the Max capability of the PS.

Off the cuff - I wouldn't do it.
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 Your question falls squarely in the "if you have to ask, you shouldn't be messing with it" category. That is not to put you down, but rather to just let you know that your question falls both within the technical world of AC power distribution and the world of local and state laws and code requirements.

 This board is not the proper forum to try and give you such answers as such laws and codes vary where one lives in the world, and as we are pretty well globally spread out on this forum, even in the English sections, I would not recommend anyone try and give you specific answers to your question. A local licensed/qualified electrician is who you should be asking your questions of, if your intent is to actually build/wire/power something using AC power.

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« Last Edit: February 04, 2013, 10:05:36 pm by retrolefty » Logged

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ignoring the law, can that setup 'technically' work without overheating?
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I can already draw 12V, 7A DC through a 6ft length using one twisted pair just fine..

That seems to me about ten times too much current for a CAT5 cable. If you were planning to use RJ45 or similar connectors, I'm sure you'll find they have a very low current rating too.

I think you're also exceeding the rated voltage by about a factor of two.

Bottom line is that this is the wrong cable for the job.

ignoring the law, can that setup 'technically' work without overheating?

Ignoring the law, it's unsafe. Given that you clearly aren't familiar enough with electrics to understand that for yourself, I recommend that you stick to using cables within their rated capacity and aim to comply with building standards in your area. Not necessarily because it would be necessary for your work to be legal (although that's a good reason) but because it means that you can know that what you're doing is safe.
« Last Edit: February 04, 2013, 10:18:19 pm by PeterH » Logged

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For what it's worth, this Wikipedia article says it's good for .577 A per conductor and 125VDC. Seems there are 8 conductors per wire so that gives you under 5A per wire; your 7A is asking for trouble.

I'm not able to comment on the VDC vs VAC thing....

But I'll go with lefty (as usual  smiley-cool ) and others on this: don't mess with stuff like this when you don't understand it. It's not worth the risk.

Have to ask: why are you asking?- you have lots of surplus wire?

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Why would you even want to do this? Cat5 isn't any cheaper or easier to use. If you're looking for a power over Ethernet solution for 12v, many already exist.
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Without knowing what you exactly looking for, but have an idea (individual PoE) I would NOT do it in the way you asked.

IF you consider some sort of PoE for devices that are kind of "energy hungry", your first thought in principle is right: the higher the Voltage, the lower the current on wire, the lower the voltage loss on the cable (you will not see anything close to 12V at the end if you input 12V and having a 100ft cable).

That's (and staying in the "safe voltage region) why they use 36 / 48V for PoE. It allows for enough loss on the cable with still enough input Voltage to make a step down regulator do the propper job for your application. You should also consider this path.

120V AC directly on a cat cable is defo out of specification and could cause significant trouble from a law and responability side! Keep in mind that not only the specification of a cable counts, also the usecase and the surrounding! In many countries, you will not be allowed to use a 120V AC cable sitting directly attached to a PELV using cable.
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Can I ask why you want to do this in the first place? Maybe if you explain your needs better somebody can recommend a better solution. Why not just use the proper cable for carrying 120VAC to begin with?
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For what it's worth, this Wikipedia article says it's good for .577 A per conductor and 125VDC. Seems there are 8 conductors per wire so that gives you under 5A per wire; your 7A is asking for trouble.

And since the peak value of a 120VAC sine wave is around 170V, the answer to the original question should be abundantly clear.

Too often on this forum we are presented with a solution rather than a problem, and asked, "Will it work?" Not only can this be difficult to answer without knowing the problem, but it precludes alternate suggestions that may represent improvements on the original "solution".

In this case the answer is clear: Yes, this could very well cause a fire as the cable is clearly being operated beyond its specifications, relative to both current and voltage.

At the risk of sounding like a broken record (remember records?), I will ask again: Why do you want to do this?
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I need to power something 100ft+ away with an ethernet cable. The load is 12V and ~7A. If I use AC, I can convert it to DC at the end of the cable. The cable will greatly vary in length from 6ft to 100ft+ so the solution needs to work with either scenario.
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I need to power something 100ft+ away with an ethernet cable.
Wireless was made so that, you don't need to do this. Your setup is very dangerous, and should not be done like that.

If you do this and get hurt, it's sad to say but, it's on you.
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I need to power something 100ft+ away with an ethernet cable. The load is 12V and ~7A. If I use AC, I can convert it to DC at the end of the cable. The cable will greatly vary in length from 6ft to 100ft+ so the solution needs to work with either scenario.

That's about 85W. If you ran about 50V DC at 2A using all eight conductors (four each way) you would just about be able to carry that while staying within the wiring spec. Do you need this cable to carry data as well? I would assume not, since your proposed data and AC in the same bundle is not a happy combination. You'd need to provide a DC-DC converter to generate your 12V supply at the far end.

Why are you constrained to using CAT5 instead of a suitable power cable? This is not what it's designed for, and it's not good at it.
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