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Category 6 cable to power LED-strips


diderik

Question

Would you recommend this? I.e. using category 6 cable from the controller to power 12V LED-strips? We're not talking long stretches of cable, 3-4 m at the very most.

I have tried to look up the specs and doing some calculations, but I'm none the wiser.

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That depends a bit on what load you intend to have. CAT6 seems to be available with AWG22-AWG24. Worst case would be a length of AWG24 of 8 meters in your case. With a resistance of some 85 mOhm/m and a total length of 8 m (back and forth to the strip) you would have a resistance of about 0.68 Ohms which with a load of 5 A (not unreasonable) would have a drop of 3.4 V out of 12 V if that's what you're using.

I'd say go with something thicker...

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Guest gembrain

There are plenty of volt drop calculators you can use on the net. The one I use is at www.calculator.net

What is a pain though is that the strip suppliers don't really give enough info.

e.g. If you have RGBW then you've got 4 cables + common. They don't all carry the same current.

Make sure your strip is not too long. e.g. if you have a 5 metre strip powered one end only then you are most unlikely to get an even brightness along the strip - so you need to power from both ends.

You could experiment using your CAT6 and at different brightness levels measure the voltages for each channel where it connects to the strip. Certainly try combining several cores for the common connection.

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  • Inquirer
  • My instinct would be to go for something thicker, too. Trouble is, my electrician has already hooked it things up with cat6. I had a look up there because I thought the wattage reported by the controller was a bit low, around 15% lower than I would expect as compared to testing the strip before installation. Of course, that is a calculation based on on one strip directly connected to the controller; I don't know whether multiple connections (thin or thick wire) would matter.

    @ gembrain: I did not see your post until after I posted.

    Yep that's true. In my case W carries more than R+G+B, and 5m does not draw anywhere near 72W as stated. I've tried two different volatge drop calculators, and they provided widely conflicting answers...

    With the strips installed, everything does actually look rather good, but does anyone know how much current a single strand of cat6 is rated for? I've looked verywhere. Being AWG24 or thicker, I found a table telling me I should be fine, but looking at the specs for PoE, it's like 360mA?

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    Guest gembrain

    diderik, You might find this link interesting....

    Please login or register to see this link.

    Let us know how you get on.

    I have noticed that electricians don't seem to know enough about LED stuff. Mine said bell wire would do - much same as your CAT6. Generally it won't do at all!

    [ Added: 2014-09-18, 16:48 ]

    In terms of what rating a cable can take it depends upon ambient temperature, what temperature the cable insulation can take and how it is installed. A 1mm cable plastered into your house wall can take a great deal more than the same cable run through the middle of insulation in a stud wall.

    2.5mm standard cable is rated 27 amps before any derating factors.

    0.75 is 6 amp.

    0.5mm is 3 amp

    CAT6 is about 0.25mm CSA - so definitely low currents only!

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    If you have RGBW then you've got 4 cables + common. They don't all carry the same current.

    Except perhaps return/GND which carries the sum of the others.

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  • I talked to the electrician today -- he said the cat6 cable was as thick as the rgbw cable I had provided (an insufficient amount of), and he had used double strands, like everyone did on LED-strips. The result looks good though, so I hope I'm alright...

    gembrain: I read your link. Thinking about it, full power on RGB alone + full power on W alone would nearly add up to 72W (when testing the 5m strip). However, full power on RGBW (all four channels together) draws a lot less current.

    (And no, it's not the driver -- it was plenty powerful. And in preinstallation testing I used very short cables.)

    I never tested powering the strips from both sides, but there was (and is) no visible difference in luminosity in each end of the strip.

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    I talked to the electrician today -- he said the cat6 cable was as thick as the rgbw cable I had provided (an insufficient amount of), and he had used double strands, like everyone did on LED-strips. The result looks good though, so I hope I'm alright...

    gembrain: I read your link. Thinking about it, full power on RGB alone + full power on W alone would nearly add up to 72W (when testing the 5m strip). However, full power on RGBW (all four channels together) draws a lot less current.

    (And no, it's not the driver -- it was plenty powerful. And in preinstallation testing I used very short cables.)

    I never tested powering the strips from both sides, but there was (and is) no visible difference in luminosity in each end of the strip.

    The problem here is that you can't calculate the separate channels and then add.

    The voltage drop changes when using all channels.

    Its known that if you buy a 72W / 5m cable you newer get that actual power stated. (almost)

    Almost ALL suppliers lower the voltage on the LED strips to get longer lifespan = less heat.

    So they lover the voltage across the LEDs to something like 10-11V.

    Thats why you get 72W when increasing the voltage to 14.4.

    So if you want true 5W buy 7W, if you want true 7W buy 10W and so on..

    Thats just the way it is.

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  • Yep, I accept that's the way it is, but I hate it when numbers don't add up...

    Why does the voltage drop increase when using all channels? Are they not connected in parallel?

    (Bear with me, I'm no electrician, I just took som basic physics in college.)

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    diderik, You might find this link interesting....

    Please login or register to see this link.

    Let us know how you get on.

    I have noticed that electricians don't seem to know enough about LED stuff. Mine said bell wire would do - much same as your CAT6. Generally it won't do at all!

    [ Added: 2014-09-18, 16:48 ]

    In terms of what rating a cable can take it depends upon ambient temperature, what temperature the cable insulation can take and how it is installed. A 1mm cable plastered into your house wall can take a great deal more than the same cable run through the middle of insulation in a stud wall.

    2.5mm standard cable is rated 27 amps before any derating factors.

    0.75 is 6 amp.

    0.5mm is 3 amp

    CAT6 is about 0.25mm CSA - so definitely low currents only!

    Well this is truth with modification, you always have to consider the voltage.

    With a higher voltage you can deliver much high wattage on the same current.

    (POE is 45-55V i think)

    Wattage is key here.

    Led stripes for calculation = 5M 14,4W/m

    Using your cable rating = P (Watt) = U (voltage) * I (Amps)

    P=U*I = xW

    Using 24 led strips you get

    3A*24V = 72W (max per channel or wire)

    Using 12V led strips you get

    3A*12 = 36W (max per channel or wire)

    So on a 24V RGBW led stripe you have 4 channels.

    72 / 4 = 18W

    18W/ 24V = 0,75A!

    RGB 3 channels

    72W / 3 = 24W

    24W / 12V = 2A!

    Remember this is on 5m led stripes. Divide the numbers to suit your needs.

    With this in mind you can easily use a cat6 cable but use 2 or more cables on the return channel for the voltage drop and current to be sure depending on your usage case.

    On another note, consider how thin the copper tracks in the led strip are.

    Use bell wire, cat 6, cat 5 it doesn't matter unless you get clear shifts in voltage etc..

    [ Added: 2014-09-19, 15:56 ]

    Yep, I accept that's the way it is, but I hate it when numbers don't add up...

    Why does the voltage drop increase when using all channels? Are they not connected in parallel?

    (Bear with me, I'm no electrician, I just took som basic physics in college.)

    Well to put it in an easy way.

    The more current you use the more resistance the wire creates.

    Resistance = Voltage / Current

    R = U/I

    Therefore: More current increase the resistance of the cables and the voltage then decreases due to increased resistance of the cables.

    Thats why we use high voltage when transferring power long distance.

    And as I (current) is a product of U (voltage) and R (resistance)

    I= U/R

    Increase R and I also goes down, because you get lower total power as P = U*I

    And this is very easily explained and actually not really related to the general function of led stripes but it is a function of current traveling through copper wire.

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  • Thanks a lot! The first part explaining why cat6 will do, put my mind to ease.

    The second part about increased voltage drop when using all four channels; I'm not sure I follow

    The more current you use the more resistance the wire creates.

    Resistance = Voltage / Current

    R = U/I

    Isn't the principle of Ohm's law that R is a constant? So what you're saying is that more current changes this constant, and then we can use Ohm's law to do the math? Otherwise, more current should lead to decreased resistance?

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    Thanks a lot! The first part explaining why cat6 will do, put my mind to ease.

    The second part about increased voltage drop when using all four channels; I'm not sure I follow

    The more current you use the more resistance the wire creates.

    Resistance = Voltage / Current

    R = U/I

    Isn't the principle of Ohm's law that R is a constant? So what you're saying is that more current changes this constant, and then we can use Ohm's law to do the math? Otherwise, more current should lead to decreased resistance?

    Yes you are right, R is alway constant, i tried to put it in a simple way..

    What i should have said is that the more current you use the more voltage drop across the wires you get.

    Let´s say we have the following parameters.

    U = 12 Volts

    Rd = 1 Ohm (Resistance of wire used and the internal wire of the LED strip)

    I1 = 2A Current when using 1 LED

    I2 = 4A Current when using 2 LED´s

    Ud = Voltage drop on the cable

    So lets go

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    /emoticons/default_icon_smile.gif" alt=":-)" />

    1 led driven:

    U = 12V

    I1 = 2A

    Voltage drop cable 1

    Ud = I1 * Rd = 2 * 1 = Ud = 2 Volts

    Voltage across the leds

    U1 = U - Ud = 12 - 2 = 10V

    So total power using 1 led channel

    W1 = U1 * I1 = 10 * 2 = 20W Total channel power.

    So thinking the way 2 channels should be 20W + 20W = 40W right?

    But it doesn't work this way.

    Using 2 leds would be 4 amps right? using this we get:

    2 led´s driven:

    U = 12V

    I2 = 4A (double the leds)

    Voltage drop cable 2

    Ud = I2 * Rd = 4 * 1 = Ud = 4 Volts (Increase in voltage drop due to higher current)

    Voltage across the leds

    U2 = U - Ud = 12 - 4 = 8V

    So total power using 2 led channels

    W2 = U2 * I2 = 8 * 4 = 32W Total channel power! AHA!

    So here you can se that the voltage drop over the wires affect the total system power

    and that's why adding all separate leds will never work.

    Hope this explains it to you

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    Guest gembrain
    Thanks! That did it. Increased current means increased voltage drop...

    Note that increased current also means more heat in the cable - and that is what determines the capacity of the cable. Basically how much heat it can take before either the wire or the insulation melts or breaks down.

    I think Cat 6 is rated 60 deg C

    The 360mA capacity that you found is also what I found - but that is for one core.

    To be on the safe side just check that the cable is not getting too warm after the lights have been on for a while.

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    /emoticons/default_smile.png" alt=":)" srcset="https://forum.fibaro.com/uploads/emoticons/[email protected] 2x" width="20" height="20" />

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    Thanks! That did it. Increased current means increased voltage drop...

    Note that increased current also means more heat in the cable - and that is what determines the capacity of the cable. Basically how much heat it can take before either the wire or the insulation melts or breaks down.

    I think Cat 6 is rated 60 deg C

    The 360mA capacity that you found is also what I found - but that is for one core.

    To be on the safe side just check that the cable is not getting too warm after the lights have been on for a while.

    Please login or register to see this image.

    /emoticons/default_smile.png" alt=":)" srcset="https://forum.fibaro.com/uploads/emoticons/[email protected] 2x" width="20" height="20" />

    I think you have found the specifications for PoE (Power over Ethernet).

    This is a very conservative current value due to many thing´s.

    The first one is that you can have 100´s of cables lying on top of each other all with PoE injectors and that has to be taken into account for overall heat. (limiting factor)

    This specification has nothing to do with what the cable can withstand when one single wire

    is used to to power 1 led stripe.

    Same thing with "real" power cables, maximum specification can almost never be used in an office complex for example due to all the cables on the cable tray.

    I don't know what kind of dynamite insulation you use in the UK that can withstand 27A on a 2.5 mm2 wire for normal installation and usage

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    /emoticons/default_icon_smile.gif" alt=":-)" />

    In Sweden our "maximum" rating for 2,5mm2 is about 16A not using PEX insulation. (90 degree capable insulation)

    Now this is for 230V AC with brakers that deliver far more than its rating under short periods (up to the several 1000+ Amps) during a short.

    And the cable has to be strong enough to withstand all these 1000´s of amps several times.

    What we use to power led stripe´s 12V / 24V all have different security measures built in.

    Especially short circuit protection and overload protection that never lets the current free flow like this.

    I always use 24V stripes though, because of the voltage drop and the current.

    12V 14,4W/m 5m strips always dips in intensity in some part of the installation.

    Switching to 24V has removed all my problems.

    In the end you are right in saying that current / heat is the limiting factor.

    But you can use Cat 6 (AWG 23-24, 0,25mm2) for higher currents than you might think.

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    Guest gembrain

    My apologies - I don't know why I posted the 360mA limit without explaining it! It is indeed for POE situations in cabling trays where there might be 100 cables all bunched together running for 100 metres so is not comparable to this situation.

    In the UK the 27A max for 2.5mm2 is for clipped direct without ANY insulation around it or any other derating factors - so in practice you will never see a 27A circuit using one cable. Rating is for standard 70C cable insulation at an ambient 30C. I think UK is about the only country that uses ring circuits and with 2.5mm and what is effectively 2 cables you can't use more than a 32A breaker.

    I think Sweden is all radial circuits (?) and you have much better insulated homes with cables and services all run inside the walls - so your cable will be derated significantly. Even in UK virtually all radials using 2.5mm are max 20A although you will find 1.5mm 20A radials where derating is not a factor.

    Like you, all modern consumer units have current and short circuit protection but there are still many houses that do not have RCD protection and plenty with old rewireable fuses!

    I agree that CAT6 is OK for the strips if used sensibly and in the OP example it is most probably fine. However, if someone else were to maybe power 3 strips and run 3 CAT6 cables together through some insulation to get there then, regardless of voltage drop, that would be a different matter altogether.

    I just worry that maybe some people might automatically think CAT6 will always be OK for LED strips in all circumstances.....

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    My apologies - I don't know why I posted the 360mA limit without explaining it! It is indeed for POE situations in cabling trays where there might be 100 cables all bunched together running for 100 metres so is not comparable to this situation.

    In the UK the 27A max for 2.5mm2 is for clipped direct without ANY insulation around it or any other derating factors - so in practice you will never see a 27A circuit using one cable. Rating is for standard 70C cable insulation at an ambient 30C. I think UK is about the only country that uses ring circuits and with 2.5mm and what is effectively 2 cables you can't use more than a 32A breaker.

    I think Sweden is all radial circuits (?) and you have much better insulated homes with cables and services all run inside the walls - so your cable will be derated significantly. Even in UK virtually all radials using 2.5mm are max 20A although you will find 1.5mm 20A radials where derating is not a factor.

    Like you, all modern consumer units have current and short circuit protection but there are still many houses that do not have RCD protection and plenty with old rewireable fuses!

    I agree that CAT6 is OK for the strips if used sensibly and in the OP example it is most probably fine. However, if someone else were to maybe power 3 strips and run 3 CAT6 cables together through some insulation to get there then, regardless of voltage drop, that would be a different matter altogether.

    I just worry that maybe some people might automatically think CAT6 will always be OK for LED strips in all circumstances.....

    Very true, yes.

    To sum it up for all others, if you don't know what you are doing.. then don't do!

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    Ask you electrician first!

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