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I want to extend all my CR-10S wires. I have two long wire types: 22 and 18 AWG wires. I've done some research and found the following:

  • Extruder heating element: 22 AWG or lower.
  • Extruder thermistor sensor: 22 AWG or lower (Doesn't really need much amp).
  • Fans: 24 AWG or lower (Doesn't really need much amp).
  • Limit switch/filament sensor: 24 AWG or lower (Doesn't really need much amp).

Here is where I've problems determining which wire gauge to use:

  • Stepper motor wires: ?
  • Bed heater wires: ?

What's the wire gauge needed for the stepper motor and bed heater wires? Obviously, the bed heater needs more amp so I expect lower wire gauge. Is my 18 gauge wire enough for this?

On the Reprap site, it says that 18 AWG or lower is fine for the heating bed.

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2 Answers 2

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If my calculations are correct, a typical ceramic heating element for the extruder heating block runs 40 W. At 12 V dc, that equates to 3.33 A. A 24 awg wire is rated for 3.5 A, which means it barely covers the draw from the heater. A high torque Nema 17 motor will draw 2 A (which is probably heavier than most standard stepper motors in most 3D printing applications). Seeing as how the 18 awg wire is rated to 9.5 A, you should have no issue extending your wires using this gauge of wire for all of the extensions.

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  • $\begingroup$ Please do note that 3.5 A is @ 75 °C. It is about 2.1 A @ 60 °C. Usually the current is lower than 2 A for steppers. $\endgroup$
    – 0scar ♦
    Nov 27, 2018 at 12:28
  • $\begingroup$ Also worth noting that these calculations are for SOLID wires, not stranded wires. Stranded wires can carry less current. $\endgroup$
    – redfox05
    Oct 27, 2020 at 11:25
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This answer expands on the heat bed wires question which is not addressed in this answer and gives a foundation for the edit of the question stating that AWG 18 or lower is sufficient.

The current depends on the voltage your machine uses. The question does not state whether you modified the power supply or not. Typical values for the resistance of the bed are in the range of 1.2 - 1.8 Ω (Ohms). This implies a maximum current of $\frac{12}{1.2}=10 A$ (the stock power supply is 12 V, if the power supply is changed to 24 V, the current doubles). From this reference you can look up the ampacity (maximum current through a wire) which wire gauge fits the current for your application depending on the maximum temperature you want it to reach. For 10 Amps, you will see that AWG 18 can be used for a single wire when you allow the wire to heat up to 60 °C. Note that bundling wires lowers the ampacity of a wire, because the cooling is less optimal for bundled wires (this is called de-rating).

Please be careful when you read that certain wires are sufficient for your application. It is best to calculate the current your specific application draws from the power supply rather than relying on somebody else's calculation, it could well be that the assumptions are different than in your specific case. A multimeter or multitester is a valuable asset to aid in your calculations.

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  • $\begingroup$ The power supply has not being modified. What do you mean when you say "bundling wires"? $\endgroup$
    – Programmer
    Nov 27, 2018 at 8:16
  • $\begingroup$ @Programmer Wire bundling is the process where you bundle multiple wires together using e.g. sleeves or cable ties like Ty-Raps, etc. $\endgroup$
    – 0scar ♦
    Nov 27, 2018 at 8:20
  • $\begingroup$ I plan to use "Flexo PET Expandable Braided Sleeving" to keep each wire type together just like the printer did when I bought it. Is this a problem? By looking at the link you sent, it looks like it would a problem...What one do ? Let the wires hanging out just like that after extending them? $\endgroup$
    – Programmer
    Nov 27, 2018 at 8:27
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    $\begingroup$ @Programmer They'll just get hotter then, please note that AWG 18 can still transport 16 A at 90 °C. Proper silicone wrapped copper wire can go up to 200 °C (should be read on the cable mantle). You might as well go for some proper AWG 16 or AWG 14, then the wires will stay cooler. I use AWG 14, but as said this is for my heat bed parameters. $\endgroup$
    – 0scar ♦
    Nov 27, 2018 at 8:48
  • $\begingroup$ Ok. It looks like I have to order AWG 14. Thanks for your help. $\endgroup$
    – Programmer
    Nov 27, 2018 at 8:53

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