So I've been designing a wiring harness PCB for my 3D printer to provide connections and easily swappable tools. I settled on a TE 34-pin connector to use as input on the PCB. The current design includes everything I need for any of my tools except the heater cartridge for the hotend. Everything is running over 20awg stranded copper wire.

My concern for the heater cartridge was that, despite 20awg being able to carry the <2A load, the fact that the heater cartridge relies on resistance in the cartridge to heat up, I wasn't sure how that would equate to usability of the 20awg and requirements for my PCB traces (if there's any change at all given the amperage for any other use).

So, my questions are:

  1. Should I pair 2x 20awg wires for each of the nominal leads of the heater cartridge, or would a single wire on each side work fine?
  2. Given that the use end of the circuit is designed for high resistance, will the PCB traces need to be wider for any reason? Would the connectors on the PCB need additional thermal relief at all?
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    \$\begingroup\$ Just because a wire can carry the current doesn't mean it will meet your needs. Always calculate the voltage drop for any power wiring. \$\endgroup\$ – Mattman944 Jun 19 '19 at 15:48
  • \$\begingroup\$ @Mattman944 yes, definitely. The 20awg shows a ~1% voltage drop up to about 1.7m (the run of wires is about 1.2m). I think my concern or uncertainty is mostly around the fact that it leads to a resistive device. Not something I’ve generally wired for in the past. \$\endgroup\$ – Jesse Williams Jun 19 '19 at 15:56
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    \$\begingroup\$ A resistive load is the least fussy of all, if your voltage drop is acceptable you should be fine. \$\endgroup\$ – Mattman944 Jun 19 '19 at 16:56
  • \$\begingroup\$ @Mattman944 ah good to know. Thank you. \$\endgroup\$ – Jesse Williams Jun 20 '19 at 2:53

The connector pins and wire are not your major concern. The traces would have less “ampacity” unless designed for greater max current in event there is no PTC or fuse protection. Web data exists for these trace “ampacity ratings” as well as free Saturn PCB software.

Ohm’s Law defines each power and return voltage drop or power dissipation per unit.

If you expect hot power connect or disconnect or contact oxidation from salt spray , that certainly helps with redundancy. Otherwise if it has bifurcated contacts, these provide contact redundancy on connector sockets.

Your connector is rated for 15A and is flash gold plated for corrosion improvements. Most contacts rated for =2A offer gold plating, but this one is better unless arcing on emergency “hot” disconnect may “pit” the gold plating on the surface 10u” flash gold from cable inductance. But you would not expect to do this.

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    \$\begingroup\$ No, definitely would not expect that. So contact redundancy would be the only benefit? If that’s the case, a single pair of 20awg should fit the bill fine for 24v/40W at ~1.5m. \$\endgroup\$ – Jesse Williams Jun 20 '19 at 2:53

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