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How many mA @ 5v can you pass through Cat5?

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alokw

New Member
Here's an easy one for ya:

How many mA at 5 volts can you safely pass through one of the eight conductors in Cat5 cable? Details of the cable and connector are below.

I'm hoping to use the cable to power low-voltage LEDs, and am wondering how many I can power using just the Cat5 cable. The overall length of the run won't surpass 50'. I will be using PWM to dim them.

- 350 MHz
- 50-micron gold plated RJ-45 connectors
- 24 AWG Stranded Copper
- PVC jacket

Thanks!
 
Last edited:

Torben

Well-Known Member
Here's an easy one for ya:

How many mA at 5 volts can you safely pass through one of the eight conductors in Cat5 cable? Details of the cable and connector are below.

I'm hoping to use the cable to power low-voltage LEDs, and am wondering how many I can power using just the Cat5 cable. The overall length of the run won't surpass 50'. I will be using PWM to dim them.

- 350 MHz
- 50-micron gold plated RJ-45 connectors
- 24 AWG Stranded Copper
- PVC jacket

Thanks!
Howdy!

The first link which comes up if you Google 'awg 24 current' is this one: American Wire Gauge table and AWG Electrical Current Load Limits

From this, it seems that a conservative rating for 24 AWG is 577 mA. You might get more than this but since the wires are in a CAT5 jacket and have other wires in there with them (i.e., they're not in free air and so cannot radiate heat freely) I wouldn't push it too much.


Torben
 

MrUmunhum

New Member
Use the calculator

.577 Amps is at 0 length. Plug in these values in their calculator:
  • Select American Wire Gauge (AWG) Size: 24
  • Select Voltag: 6v
  • Enter 1-way circuit length in feet (the calculation is for the round trip Distance): 100
  • Enter Load in amps: .577
  • Voltage drop: 3.045
  • Voltage at load end of circuit: 2.955
  • Per Cent voltage drop: 50.75
You need to factor in the length of the run. 3volts at the end of the wire will still fire up your LED. But that is at 6V.
 

MikeMl

Well-Known Member
Most Helpful Member
The current limit of 0.577A stems from self heating of the cable itself. If the goal is to deliver 5V at 0.5A to the far end of an arbitrarily long cable, why don't you start with a higher voltage and then put an IC voltage regulator like a LM7805 at the far-end of the cable to regulate the voltage to the load.
 

dknguyen

Well-Known Member
Most Helpful Member
To add on to MikMI's idea, you could also reduce the current sent along the wire if you used sent a higher voltage, but rather than a linear regulator, use a switching converter at the other end.

Higher voltage with a linear regulator would overcome the resistive voltage drop, but would not help transmission current levels. A lot simpler though.
 

microtexan

New Member
Are you sure this is Cat 5 cable with stranded wires? I don't believe I've ever seen that.
 

Sceadwian

Banned
Must be a mistake Texan, because Cat3 and Cat5 are both solid core. If it's stranded it's not cat5. Keep in mind if you're not using the rest of the wires in the cable you can simply tie half of the pairs together for VCC and half for GND, which would give you the equivilant of 18 gauge wire, according to the linked chart that's up to 16 amps.
 

Dean Huster

Well-Known Member
The only CAT5 cable I've ever used (and installed connectors on, etc.) had stranded conductors. Otherwise, flexibility is the issue and if it has to be run in conduit, it MUST be flexible. Can you imagine running Romex in 1" conduit?

Dean
 

Sceadwian

Banned
That's funny Dean, cause until I looked it up I didn't even realize that Cat5 could be stranded =) I've done a few dozen network installs some on a professional basis and it's always been solid core, I've run it through short conduits but most of the runs are through walls so extreme flexibility isn't much of an issue. I guess I learn something new every day =)
I like the solid core stuff myself, at least for hobby use. I got the tail end of a spool from the last time I wired a network and I use it all the time.
 

Ross Craney

New Member
@Dean - ALL Cat 5 , 5e , 6 etc I have used have been solid core. NEVER seen stranded. A quick look at TIA , ISO standards really only appear to give performance standards , not manufacturing standards.
However , if you are using IDC fittings on stranded cable you should be shot.
 

Sceadwian

Banned
I looked up the Wikipedia entry and it says it comes in stranded, I didn't look up any standards though, I tend to trust wiki a little too much. But it does make sense now that I think about it. Some of the patch cables I have are too flexible to be made out of solid core wire. A lot of the work we did was to punch down blocks and solid core gets better electrical contact than stranded.
 

AlexR2

New Member
Stranded cat5 is only used for patch cords and is not suitable for long runs. Cat5 cabling installed throughout a building usually is solid cored.
 

Leftyretro

New Member
From Wikipedeia:

Connectors and other information
The cable exists in both stranded and solid conductor forms. The stranded form is more flexible and withstands more bending without breaking and is suited for reliable connections with insulation piercing connectors, but makes unreliable connections in insulation-displacement connectors. The solid form is less expensive and makes reliable connections into insulation displacement connectors, but makes unreliable connections in insulation piercing connectors. Taking these things into account, building wiring (for example, the wiring inside the wall that connects a wall socket to a central patch panel) is solid core, while patch cables (for example, the movable cable that plugs into the wall socket on one end and a computer on the other) are stranded. Outer insulation is typically PVC or LSOH.

Lefty
 
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