Author Topic: Amps over cat5  (Read 4743 times)

Offline Jeffl

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Amps over cat5
« on: January 22, 2016, 03:33:56 PM »
I have read different things and used different calculators and I'm still not sure.  What is the safe rating for amperage over cat5 when using 4 ground wires and 3 for power?

Offline tbone321

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Re: Amps over cat5
« Reply #1 on: January 22, 2016, 04:56:06 PM »
I believe that the rating for Cat5 POE is 1.5A per pair.  You have 3 pairs so that would be 4.5A.  The added ground may help a little with voltage drop but does not increase the current rating.

Offline Phrog30

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Re: Amps over cat5
« Reply #2 on: January 22, 2016, 05:09:51 PM »
Most cat5 is 24ga which is around 0.5a per wire. So one pair is close to an amp.

James

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Offline tbone321

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Re: Amps over cat5
« Reply #3 on: January 22, 2016, 05:57:12 PM »
It doesn't really work that way.  Unless that pair of wires is in parallel with each other, there is no addition in current capability and in what we are doing, the pair is in series.  That .5A is also based on 120VAC and that is not what we are putting on the cable.  If you were to look at the automotive charts, they show 25ga pulling 2A for 80 feet.  The RJ45 is rated for 1.5A per terminal and that is for the most part what we go by and just like the wire, only parallel pairs add up to increased current capacity.  Many will put 4A fuses on these connections to give a little headroom and I have yet to see anyone talking about burnt wires so far.

Offline Phrog30

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Re: Amps over cat5
« Reply #4 on: January 22, 2016, 06:10:14 PM »


It doesn't really work that way.  Unless that pair of wires is in parallel with each other, there is no addition in current capability and in what we are doing, the pair is in series.  That .5A is also based on 120VAC and that is not what we are putting on the cable.  If you were to look at the automotive charts, they show 25ga pulling 2A for 80 feet.  The RJ45 is rated for 1.5A per terminal and that is for the most part what we go by and just like the wire, only parallel pairs add up to increased current capacity.  Many will put 4A fuses on these connections to give a little headroom and I have yet to see anyone talking about burnt wires so far.

Man, I thought it was obvious that they would be in parallel. I didn't think I needed to go captain obvious on that. :P

Here's what I read:
https://en.m.wikipedia.org/wiki/Power_over_Ethernet#Standard_implementation


James

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Offline Jeffl

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Re: Amps over cat5
« Reply #5 on: January 22, 2016, 06:45:24 PM »
I did some searching and found this from David.  I did a test with 169 12v nodes and it was taking 3.2amp.  I figured I was pushing it.

http://blog.holidaycoro.com/2013/03/a-technical-guide-to-rgb-wire-selection.html


Offline gadgetsmith

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Re: Amps over cat5
« Reply #6 on: January 22, 2016, 06:58:26 PM »
There are many things that go into how many amps can be carried on CAT cable. Trust me when I say voltage drop will be the limiting factor in how many amps you decide to put thru a CAT cable.  I've run 150 nodes at 12v, 4.5amps thru a 22ft CAT cable, with a (basically) zero rise in temperature over ambient (which was about 63F).  Voltage drop on some strings was unacceptable, while on other strings it was fine.

I've also created a 6ft extension cord from CAT cable and run a portable electric heater running at 1250W for over 15 minutes (roughly 11 amps and 116VAC), with an temp rise to approx 95 F (~30F rise in temp)

There is so much misinformation floating around and people quoting numbers from tables off the internet, but there are many factors that effect the reported numbers in those tables.

I won't sit here and say that CAT cable is the best stuff in the world for our application,  as the physical construction isn't designed for outdoor use like we're using it, but there is plenty of capacity when using 2-3-3 or 1-3-4 type weekend for pixel strings. Personally, I limit CAT cable to 5 amps as this is the fuse rating provided on most pixel controllers, and that is how I do it.  You remove fusing and power inject a ton of pixels, then you should check what you are doing through testing.


Offline tbone321

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Re: Amps over cat5
« Reply #7 on: January 22, 2016, 07:05:36 PM »


It doesn't really work that way.  Unless that pair of wires is in parallel with each other, there is no addition in current capability and in what we are doing, the pair is in series.  That .5A is also based on 120VAC and that is not what we are putting on the cable.  If you were to look at the automotive charts, they show 25ga pulling 2A for 80 feet.  The RJ45 is rated for 1.5A per terminal and that is for the most part what we go by and just like the wire, only parallel pairs add up to increased current capacity.  Many will put 4A fuses on these connections to give a little headroom and I have yet to see anyone talking about burnt wires so far.

Man, I thought it was obvious that they would be in parallel. I didn't think I needed to go captain obvious on that. :P

Here's what I read:
https://en.m.wikipedia.org/wiki/Power_over_Ethernet#Standard_implementation
 
James

Sent from my SM-G900V using Tapatalk

Sorry to burst your bubble there captain obvious, but what you thought of as obvious is incorrect.  If you have one positive wire and one negative wire (1 pair), they must be in series with the load or there is no circuit and wires in series don't add capacity, only length.

Offline Phrog30

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Re: Amps over cat5
« Reply #8 on: January 22, 2016, 07:12:34 PM »


It doesn't really work that way.  Unless that pair of wires is in parallel with each other, there is no addition in current capability and in what we are doing, the pair is in series.  That .5A is also based on 120VAC and that is not what we are putting on the cable.  If you were to look at the automotive charts, they show 25ga pulling 2A for 80 feet.  The RJ45 is rated for 1.5A per terminal and that is for the most part what we go by and just like the wire, only parallel pairs add up to increased current capacity.  Many will put 4A fuses on these connections to give a little headroom and I have yet to see anyone talking about burnt wires so far.

Man, I thought it was obvious that they would be in parallel. I didn't think I needed to go captain obvious on that. :P

Here's what I read:
https://en.m.wikipedia.org/wiki/Power_over_Ethernet#Standard_implementation
 
James

Sent from my SM-G900V using Tapatalk

Sorry to burst your bubble there captain obvious, but what you thought of as obvious is incorrect.  If you have one positive wire and one negative wire (1 pair), they must be in series with the load or there is no circuit and wires in series don't add capacity, only length.
I guess I'm not speaking English, I'm letting this one go.

My answer for current on 24ga wire is 0.5a, I'm rounding down. The link David posted agrees, however he's rounding up to 0.6a.

James

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Offline tbone321

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Re: Amps over cat5
« Reply #9 on: January 22, 2016, 07:24:12 PM »
We may in fact be talking about two different points without making it clear what each is and I agree, it's best simply to drop it now.  There is no point in starting a pissing match over something like this.

Offline gadgetsmith

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Re: Amps over cat5
« Reply #10 on: January 22, 2016, 08:49:22 PM »


My answer for current on 24ga wire is 0.5a, I'm rounding down.

I simply can't comprehend this answer. What is this based on?

Are we talking POE applications using POE devices? ... or are we talking twisting wires of a length of bulk CAT cable together and soldering on a pigtail/jst type connector to power some pixels from our controllers? Two completely different things. 

The 0.5 amp listing seen in many online tables for 24 gauge wire is based on what is commonly accepted as a "very very conservative" 700 circular mils per amp rule.  That number is based on thermal considerations of a solid 24 gauge wire being used in a transformer winding, where heat dissipation is severely limited.  As a reference, the conservative house wiring standards are based on 300-350 circular mils per amp.

Offline corey872

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Re: Amps over cat5
« Reply #11 on: January 23, 2016, 08:54:14 AM »
There is only one clear answer here...put current on your line until the wires burn up, and then back her down a smidge.

Seriously, though - as shown above, there are complicating factors here:

Your run of 3 power / 4 ground will help a bit with volt drop on the ground side, but current carrying would be limited by the three wires.  Seems like some tables are rating 'per pair', so that would be 1.5 pair in that consideration.

Then some tables list different amps for 'chassis' wiring and some for 'power transmission'.

Still other tables take into account temperature rise and may set some arbitrary limit.  Obviously if I'm in an airplane, I want a bit more safety factor in that wire than something laying out in the yard.

It might even be a case that as you run very long lengths, of nodes, voltage drop, ground line loading, etc are going to be the limiting factors way before amp capacity.


So in summary, many factors go into how much current the wire can carry...length of the run, is the wire bundled or 'open air', intermittent or long duration use, AC/DC current, safety factor, etc.  I've seen numbers anywhere from 0.5A to 3.5A per 24AWG wire, suggesting 1.5 to 10.5A for your set-up. 

Knowing most people set the max at 5 amps, it's in the middle of that range, and I have not heard of an instance of 'burning wire' at 5A yet,  I'd look at that as an average.   ....then decide if you want to be average, too...safer with less amps, or push the limit with more amps.
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Offline Jeffl

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Re: Amps over cat5
« Reply #12 on: January 23, 2016, 09:14:31 AM »
Thanks for the discussion everyone.  This will be helpful for others as they find it.  And if somebody want's to do an experiment on seeing what they will really handle please create a video so we can all get a laugh out of it instead of someone having a real issue. :)

Offline Phrog30

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Re: Amps over cat5
« Reply #13 on: January 23, 2016, 10:22:00 AM »


My answer for current on 24ga wire is 0.5a, I'm rounding down.

What is this based on?

Based on the initial question of current over cat5, which most is 24ga.

Here's another link that supports my answer.  https://en.wikipedia.org/wiki/Category_5_cable

I like corey872's answer, load it up until it burns then you know you went too far.  I start at book answers and confirm with real world testing.  However, I don't use cat5 cable for mass power distribution, I use the "correct" wire/cable. 

James

Offline gadgetsmith

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Re: Amps over cat5
« Reply #14 on: January 23, 2016, 07:03:41 PM »
My answer for current on 24ga wire is 0.5a, I'm rounding down.

What is this based on?

Based on the initial question of current over cat5, which most is 24ga.

Here's another link that supports my answer.  https://en.wikipedia.org/wiki/Category_5_cable

I meant what assumptions were made for your posted answer of 0.5 amp.  You did provide a link, but examining the footnotes, shows that it's based on the same number I stated in my post; 700 circular mills per amp.  This is very conservative, and inaccurate number, for how we are really using the cable.  Another conservative number is 300-350 circular mils per amp, which is used to create ampacity charts for house wiring...  12 gauge for 20 amp service, 14 gauge for 15 amp service... etc.

Quote
I like corey872's answer, load it up until it burns then you know you went too far.  I start at book answers and confirm with real world testing.  However, I don't use cat5 cable for mass power distribution, I use the "correct" wire/cable. 

Honestly, I love this answer.  Only wish I had the knowledge to create a dummy load and test cable to failure.  I know I could dead short the wire, but that would likely cause the PS to shut down, so i'll need to read up a bit more for a test of this sort.  Maybe then we could truly quantify CAT cables abilities. ??

As far as your "correct wire/cable" comment I can only assume you have a predisposition to something other than CAT cable? (not sure)  Personally, I'll use whatever gets the job done.  I use mostly CAT, but not all.  I only respond to these ever increasing posts as I feel it's misinformation.  I can clearly demonstrate that CAT able is not limited to 0.5amps (disregarding voltage drop), so i'm not sure where the skepticism lies?

 

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