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Using Arduino => Project Guidance => Topic started by: David82 on Feb 05, 2013, 02:58 am

Title: Will this setup cause a fire?
Post by: David82 on Feb 05, 2013, 02:58 am
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..
Title: Re: Will this setup cause a fire?
Post by: zoomkat on Feb 05, 2013, 03:03 am
Do a test with a 6' run, and if it survives, the longer runs may also survive.
Title: Re: Will this setup cause a fire?
Post by: Quick5pnt0 on Feb 05, 2013, 03:20 am
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.
Title: Re: Will this setup cause a fire?
Post by: modeller on Feb 05, 2013, 03:23 am

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.
Title: Re: Will this setup cause a fire?
Post by: retrolefty on Feb 05, 2013, 03:49 am
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.

Lefty
Title: Re: Will this setup cause a fire?
Post by: David82 on Feb 05, 2013, 04:09 am
ignoring the law, can that setup 'technically' work without overheating?
Title: Re: Will this setup cause a fire?
Post by: PeterH on Feb 05, 2013, 04:14 am

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.
Title: Re: Will this setup cause a fire?
Post by: JimboZA on Feb 05, 2013, 05:37 am
For what it's worth, this Wikipedia article (http://en.wikipedia.org/wiki/Category_5_cable) 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  8) ) 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?

Title: Re: Will this setup cause a fire?
Post by: wizdum on Feb 05, 2013, 05:54 am
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.
Title: Re: Will this setup cause a fire?
Post by: jwka on Feb 05, 2013, 10:11 am
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.
Title: Re: Will this setup cause a fire?
Post by: Quick5pnt0 on Feb 05, 2013, 12:19 pm
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?
Title: Re: Will this setup cause a fire?
Post by: JChristensen on Feb 05, 2013, 01:49 pm

For what it's worth, this Wikipedia article (http://en.wikipedia.org/wiki/Category_5_cable) 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?
Title: Re: Will this setup cause a fire?
Post by: David82 on Feb 05, 2013, 03:13 pm
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.
Title: Re: Will this setup cause a fire?
Post by: HazardsMind on Feb 05, 2013, 03:27 pm
Quote
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.
Title: Re: Will this setup cause a fire?
Post by: PeterH on Feb 05, 2013, 04:51 pm

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.
Title: Re: Will this setup cause a fire?
Post by: tack on Feb 05, 2013, 04:53 pm
The cable isn't rated for AC. You'll probably find leakage currents that it's not designed to withstand. This can cause stress in the insulation and ultimately a breakdown.

It's also not rated for current. With such a small CSA conductor you'll have excessive volt drop over a long length and also heating effects in the cable. Heat + PVC insulation = bad. The rating of the insulation will be less when hot and you risk melting it.

Transforming to 12V, rectifying and drawing 7A at the end means your 120V AC RMS current will be in the 0.7A+ region. The exact figures will depend on I2R losses, transformer iron and copper loses and overall efficiency.

Bottom line, No, it's not suitable for mains voltage like you are proposing.

If you need a run like that then use a 3 core cable of 1mm upwards CSA. With current below 2A I'd probably say 1mm-2.5mm flex extension cable would suffice, without consulting tables or doing a calculation. Laying in ducts or trunking will de-rate the cable too.
Title: Re: Will this setup cause a fire?
Post by: Nikarus on Feb 05, 2013, 07:04 pm
Im just wondering. Why cat5. Its easy enough for like $30 to get a nice 100ft 12v extension cord that will mroe then run your 12A adaptor way out there.
It's not like you need to be secretive or anything with what your trying to do. Are you like trying to drive the power through an ethernet cable thats already built into a wall or something?
Title: Re: Will this setup cause a fire?
Post by: David82 on Feb 05, 2013, 09:29 pm
What other cable can carry that kind of power and data while being able to be bought locally in different lengths? Cat5 is very convenient. An extension chord would be good too but it only has 3 wires. I need power, RX, TX, and video signal all on one cable.
Title: Re: Will this setup cause a fire?
Post by: retrolefty on Feb 05, 2013, 09:45 pm

What other cable can carry that kind of power and data while being able to be bought locally in different lengths? Cat5 is very convenient. An extension chord would be good too but it only has 3 wires. I need power, RX, TX, and video signal all on one cable.


Part of most national safety codes is that one is not allowed to carry both AC power and DC signals within the same cable assembly, unless it's some specially build cable that is in effect two cables enclosed in one overall cable. This path you seem determined to keep on is with not a good one to pursue.

Lefty
Title: Re: Will this setup cause a fire?
Post by: David82 on Feb 05, 2013, 09:51 pm
OK. I need AC power, video signal, and RX, TX all on one cable. What cable will do that?
Title: Re: Will this setup cause a fire?
Post by: oric_dan on Feb 05, 2013, 10:00 pm
Quote
OK. I need AC power, video signal, and RX, TX all on one cable. What cable will do that?

It took me 3 seconds to do this search,

http://www.google.com/webhp?source=search_app#hl=en&tbo=d&sclient=psy-ab&q=ac+dc+in+same+cable&oq=ac+dc+in+same+cable&bav=on.2,or.r_gc.r_pw.r_qf.&bvm=bv.41934586,d.cGE&fp=5888ed2a9af8b67f&biw=1005&bih=828
Title: Re: Will this setup cause a fire?
Post by: Delta_G on Feb 05, 2013, 10:04 pm
The thing I don't see coming up is interference.  Your 120VAC is going to step all over your video signal and serial comms if it is in the same cable even if it didn't catch fire.
Title: Re: Will this setup cause a fire?
Post by: PeterH on Feb 05, 2013, 10:30 pm

What other cable can carry that kind of power and data while being able to be bought locally in different lengths? Cat5 is very convenient. An extension chord would be good too but it only has 3 wires. I need power, RX, TX, and video signal all on one cable.


You're mixing data and video in the same bundle as power cables? That's going to need screening then even assuming you get around the conductor rating issues. UTP is not a good starting point for that.
Title: Re: Will this setup cause a fire?
Post by: WheelerMDW on Feb 05, 2013, 11:26 pm
Believe it or not, I actually do this type of testing for a living, so let me assure you - CAT 5 cable will carry 7A of AC current for approximately 2.5 seconds before fusing.  30A will last approximately 65ms before fusing, and 60A will last approximately 13ms before fusing.

I will not state how much current can be 'safely' carried by CAT 5 cable for your own safety...

Forgot to answer the second part of the question...you asked why would 120V cause the CAT5 cable to fuse when 12DC does not:

DC current will use the entire cross-sectional area of the wire to conduct current.  I do not know what the DC current rating of CAT5 cable is, but if you say you can carry 7A DC through it, I assume the cross-sectional area of 26 AWG wire is sufficient...

With respect to AC current - as frequency increases, conductors begin to exhibit "skin effect," which is that the current actually travels on the outer surface of the wire and not through the center of the wire.  As frequency gets higher, the skin depth gets smaller, so you are effectively reducing the area that the current is flowing though, so at 120Hz, you really don't have the equivalent of 26AWG copper wiring any more - you have something less (I don't know how much less, unfortunately).  At extremely high frequencies, the entire current path may be only on the surface of the wire itself.  30 Megabit Ethernet signals are very low voltage and very low current, so the amount of copper needed to transmit the data is very small, so why then is CAT5 cable 26 AWG??

The answer is simple - the telecommunications company that is sending service into your home has engineered their protection mechanisms to ensure that the most dangerous voltages your telecomm lines will ever see is 120V.  They also know that if you should get 120V on your telecomm lines, the equipment that your telecomm lines are connected to will have secondary voltage-limiting and secondary current-limiting protection.  In short, they know you have sidactors and fuses in your equipment.  Fuses are designed to carry up to 20% above their rated spec for up to 15 minutes, so a 2A fuse will carry up to approximately 2.4A for a full 15 minutes before fusing.  Anything more than that, and the fuse operates almost immediately.  When that fuse operates, the current is interrupted and your telecomm lines don't fuse and catch your house on fire...so, that CAT5 cable has to be rated to carry up to approximately 2.5A for 15 minutes...

Hope this helps.  :)
Title: Re: Will this setup cause a fire?
Post by: David82 on Feb 06, 2013, 02:12 am
Pretend like you have a device that draws 12V 7A at most, receives TTL data, and sends back video data. It needs to operate at varying distances, say, 6-100ft. It needs to be connected with one cable. How would you do it? Do you cop out and run an extension chord for the power and a telephone/CAT5 line for the other data, or do you get smart and figure out a solution that meets the requirements?
Title: Re: Will this setup cause a fire?
Post by: modeller on Feb 06, 2013, 02:28 am

It needs to be connected with one cable.


Why one? Where did this requirement come from?
Title: Re: Will this setup cause a fire?
Post by: PeterH on Feb 06, 2013, 02:53 am
The calcs above showed that with cat5 cable in order to stay within the cable's rated voltage and current you could carry the power but it would require using all the conductors. I wonder whether you could get away with using fewer conductors if you used solid core cat6 augmented cable? That has thicker conductors and would have a significantly higher DC current rating. Since you're carrying video and TTL data down the same cable I'm pretty sure that cross-talk would render AC completely out of the question so I assume you would transmit it using DC, and keep the DC voltage within the specs for the cable which probably means 50-60V maximum. Cross-talk issues may still kill you with UTP, though. You really don't want high currents running parallel to unshielded cables.

Again, this implies transforming and rectifying the power at the supplier, and doing DC-DC conversion down to 12V at the receiver side. It seems to me that the cost / complexity added by that would outweigh the convenience of being able to use standard network cable, but I don't know how interested you are in issues other than the cable itself.

You haven't mentioned where these cables would be used. Can we assume that they would be for permanent installation in a warm dry environment?

You might be able to get away with ethernet cable if you are willing to make enough compromises, but it doesn't strike me as the right cable for carrying this much power or that combination of signals. You really need a cable designed to carry the current and voltage you need, plus separate shielded cables for the video and TTL components.
Title: Re: Will this setup cause a fire?
Post by: David82 on Feb 06, 2013, 03:25 am


It needs to be connected with one cable.


Why one? Where did this requirement come from?
Because customers would prefer to buy and string up one cable vs two side-by-side.
Title: Re: Will this setup cause a fire?
Post by: retrolefty on Feb 06, 2013, 03:39 am



It needs to be connected with one cable.


Why one? Where did this requirement come from?
Because customers would prefer to buy and string up one cable vs two side-by-side.


I figured this was for your own use. I shouldn't make such assumptions.  ;)

That's different, the customer is always right. In that case just present to and have your customer sign off on a waiver of all fault and liability for your work and run it all through your cat5 cable. Be sure you have your attorney draw up the document as some liabilities cannot be transferred or waived.

Lefty
Title: Re: Will this setup cause a fire?
Post by: Quick5pnt0 on Feb 06, 2013, 03:59 am




It needs to be connected with one cable.


Why one? Where did this requirement come from?
Because customers would prefer to buy and string up one cable vs two side-by-side.


I figured this was for your own use. I shouldn't make such assumptions.  ;)

That's different, the customer is always right. In that case just present to and have your customer sign off on a waiver of all fault and liability for your work and run it all through your cat5 cable. Be sure you have your attorney draw up the document as some liabilities cannot be transferred or waived.

Lefty


Waivers aren't going to help you when somebody gets killed. If anything it will show you knew it was dangerous and did it anyway.
Title: Re: Will this setup cause a fire?
Post by: retrolefty on Feb 06, 2013, 04:12 am





It needs to be connected with one cable.


Why one? Where did this requirement come from?
Because customers would prefer to buy and string up one cable vs two side-by-side.


I figured this was for your own use. I shouldn't make such assumptions.  ;)

That's different, the customer is always right. In that case just present to and have your customer sign off on a waiver of all fault and liability for your work and run it all through your cat5 cable. Be sure you have your attorney draw up the document as some liabilities cannot be transferred or waived.

Lefty


Waivers aren't going to help you when somebody gets killed. If anything it will show you knew it was dangerous and did it anyway.


That's why I stated the last sentence.

Title: Re: Will this setup cause a fire?
Post by: oric_dan on Feb 06, 2013, 04:31 am
Quote
Quote
Because customers would prefer to buy and string up one cable vs two side-by-side.

I figured this was for your own use. I shouldn't make such assumptions.

Actually, this makes the problem much simpler. If you sell stuff to people that connects
to the power mains, and you didn't get UL agency approval, and it burns down their house,
then you both get sued and the govt puts you in jail. Totally illogical.
Title: Re: Will this setup cause a fire?
Post by: kd7eir on Feb 06, 2013, 05:20 am
And we have documented here that David82 was repeatedly advised against such reckless behavior - that will certainly not play well in the inevitable lawsuit that David82 will be answering to, as he seems hellbent on moving forward with this blatantly hazardous endeavor.
Title: Re: Will this setup cause a fire?
Post by: JimboZA on Feb 06, 2013, 05:25 am
Quote
he seems hellbent on moving forward with this blatantly hazardous endeavor


It would be hilarious if David82's client was an Arduino hobbyist and read this thread, thinking "Hmmm, this looks just like that project at the office.... wait a minute, pretty sure it is the project at the office... does this guy know Jack Schitt about this stuff we're paying him to do?"
Title: Re: Will this setup cause a fire?
Post by: michinyon on Feb 06, 2013, 07:41 am
Some very odd claims here.   A 7A power supply is the low voltage current.   Not the high voltage current.

A 7 Amp low voltage power supply is going to be requiring well under 1 A on the mains supply side,  so as far
as current capacity is concerned,   that is the figure you should be comparing the capacity of the cable to.

You are more likely to have inadequate insulation capability,  than current constraints.
Title: Re: Will this setup cause a fire?
Post by: tack on Feb 06, 2013, 10:46 am
You'd still be running a Cat5 cable close to, or exceeding, it's DC current rating. WIth a long length than thatwll introduce I2R losses in the cable. These losses are simply heating effects due to the resistance of the conductor. That means heat. Heat means de-rating current carrying capacity AND insulation resistance.

The fact it would also be an AC supply, which the cable is NOT designed for, rings a big fat NO.

It's very very simple really, he states it's for a customer, that means you have to use materials that are rated for the purposes you want to put them to. Using a Cat5 cable for a mains AC supply is NOT what it is designed or rated for.

AC and DC are two totally different things, with different characteristics of stress and leakage currents. A cable acts like a capacitor. When you test a cable at DC it will take a charging current initially and then settle to a steady (you hope low) leakage current. If you test at AC power frequency (50 or 60Hz) that capacitance is charged and discharged repeatedly in opposite polarity and you get appreciable larger AC leakage current. It's the same as in an electronic circuit, a capacitor blocks DC and, depending on the value and applied AC frequency, will have differing effect on AC from a hgh reactive impedance to virtually none.

I get involved in low (up to 1000V) and high (up to 33,000V) testing and there are many different insulation types and ways of testing each one, from DC to AC power frequency (50 or 60Hz) and AC Very Low Frequency (0.01 to 1Hz). Insulation of a particular cable is designed to withstand the type of voltage it is intended to carry.

If you use a cable for a purposes it's not intended for then you can't guarantee how it will hold up under those conditions.
Title: Re: Will this setup cause a fire?
Post by: jeffmorris on Feb 06, 2013, 11:43 am
David82, I think that you should STOP trying to do something that may cause injury or death, and may cause damage to property. You CAN'T try to run 120VAC current through Cat5 cables. If you don't believe me, connect two thin wires to a powerful battery (battery pack for R/C cars). Touch the wires together and watch the insulation melt.
Title: Re: Will this setup cause a fire?
Post by: Krodal on Feb 06, 2013, 12:27 pm
Where can we send the electrical inspector ?
I wonder what else is terribly wrong.
Title: Re: Will this setup cause a fire?
Post by: WheelerMDW on Feb 06, 2013, 03:08 pm
Here's a simple way to look at it - there's a reason why the AC wiring in your house is 14AWG copper wiring and not 26AWG copper wiring...
Title: Re: Will this setup cause a fire?
Post by: JimboZA on Feb 07, 2013, 06:40 am

Here's a simple way to look at it


Here's an even simpler way of looking at it.... if the OP has to ask about mains wiring on a forum, he's not qualified to sign off on the work... Period.
Title: Re: Will this setup cause a fire?
Post by: PeterH on Feb 07, 2013, 05:08 pm

Here's an even simpler way of looking at it.... if the OP has to ask about mains wiring on a forum, he's not qualified to sign off on the work... Period.


There's really no getting past that.