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I'm considering using CAT6 cables to connect my printer's extruder assembly to the control board. They seem like an elegant solution, but I've read conflicting opinions online on whether or not this would be feasible.

I would like to know if CAT6 cables can handle the required current, whether I should be worried about electromagnetic interference or other problems, and how I should pair up the wires. Cable length would be 30cm max.

Here are the relevant parts:

  1. E3D heater cartridge (2 wires)
  2. E3D thermistor cartridge (2 wires)
  3. 30mm hotend fan (2 wires)
  4. Z-axis auto-leveling probe (3 wires)
  5. NEMA 17 extruder motor (4 wires)
  6. 50mm part cooling fan (2 wires)

[cable A] I imagine I would use one CAT6 cable for parts 1-4, which form a logical unit (and in the future I might combine them into a removable module). I've been given to understand that power for the fan can be spliced from the z-probe or heater cartridge, so 8 wires should be enough.

[cable B] I would use a second CAT6 cable for parts 5 and 6. There will be two spare wires, so I could potentially double the bandwidth for the motor.

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  • $\begingroup$ Don't forget about stranded vs solid. Solid wires will break quickly in moving applications. $\endgroup$ – tjb1 Dec 5 '16 at 15:43
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The ampacity question is not completely answerable because CAT6 does not specify wire gauge, so the current limit will depend on the specific gauge you get. CAT6 can be anywhere from 22 AWG to 24 AWG, and depending on who you ask this can be good for as much as 7A or as little as 0.5A. Given that you will have a bunch of wires in a bundle, this may cause them to heat up more than if they were in free air. For the steppers (1-2A) a single wire should suffice, but for the heater (around 3-4A) you might want to double up.

EMI will likely not cause any problems regardless of how you wire things up. CAT6 cables have the wires twisted in pairs of 2. Some people recommend to take advantage of these pairs: the +12V and GND of the heater should use a pair, each of the two coils of the steppers should have their own separate pairs. The reasoning behind this is that with equal current flowing in opposite directions in each wire of the pair, the generated electromagnetic fields will cancel out.

Twisted pairs are usually used when dealing with multiple pairs of wires that are carrying high frequency signals that might affect each other. The main concern for crosstalk in this application is if the stepper motor might cause the endstop to be erroneously triggered, but this is only a concern during homing when the feedrate (and thus frequency of the signal) is low anyways.

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I did this for some of the wiring on my printer, and it's working fine so far. The two cautions are:

  • At @tom pointed out, the heater is the high current item, so be careful of the wire gauge, and avoid running the wire where air can't circulate well to cool it. Wire ratings differ greatly depending on whether they're in a bundle (poor air circulation) or free.

  • For the most part I agree that EMI shouldn't be a problem -- but if you switch to thermocouples it might become a problem -- they're much more sensitive, and this might have been part of the problem I described at How to get consistent and accurate readings from thermocouples? (though alternate wiring didn't completely solve the problem in that case).

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CAT6 cable by itself is not a problem, it is typically 23 AWG solid core wire which can take you to 4A just fine. The real problem comes from the connectors you use. CAT6 usually goes hand in hand with 8p8c ethernet connectors which only have contacts rated to 500mA.

Also typically CAT6 cable is meant to be stationary (hence the solid core wires), so I'd go for something stranded. McMaster sells some nice cheap cabling that fits your needs, and it's actually meant for moving platforms like a CNC machine.

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I've used some cat 6 in one of my printers and just to be safe I used 4 wires for the extruder heat block, 2+, 2-

On the thermistors 1 is more than enough for each +/-.

I also stripped the thick shielding off and used some 'curly' cable organizer in it's place, not the shielding on the wires but the cord. So i could fit 2 cables in slightly more than the same space as one. You are probably doing this to keep it organized too but this is an option if you run out of space in your wire runs.

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