what is RK wire?

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    • #1621
      Johan von Konow

      I have got several questions regarding the wire I use to connect the components:
      First of all – The exact diameter of the wire is not critical. Any conductive wire will do.

      After lots of testing I think that 0.3mm diameter is the goldilocks option, not too stiff, and not too fragile.
      I have used strands of wire from 1.5mm RK cable (24 strands in each cable) since it can be bought in any hardware store at very low cost. The RK cable is typically used as internal wiring in fuse boxes and control units, since it is easier to bend than the cables used in the walls (with single or fewer strands that are thicker).


      Technical name is RK (H07V-K) (750/500 V), it typically follows IEC 60228 class 5. https://en.wikipedia.org/wiki/IEC_60228 and SS 424 02 31-3
      Here is one source in Sweden with an English website: https://www.biltema.se/en-se/construction/electrical-installations/installation-cables/coupling-cable-2000017929

      I’m sure that there are similar cables around the world. If you find one, please let me know the name in your region and I will update the post.

      If I try to convert the wire I used to AWG, I guess it would be something like: 14AWG24/28 or 15AWG24/29. Where the last number is most important (diameter of the strands).

    • #1632

      Thank you Johan; I learned some things today!

    • #1888

      USA* builders: I found what I think will work. I haven’t built it yet but I have printed the board, including calibrating it with the test piece (and I printed <span style=”text-decoration: underline;”>that</span> 5 times to get it right – being careful!), and I’ve test-fitted a bit of the wire I found and it seems to be very, very close.

      The answer lies in a piece of simple “zip cord“** or lamp/plug cord I had lying around that I’d cut off some dead appliance. Standard white vinyl coating, 2-conductor, goes to a 2-prong plug for a 110/120v AC wall receptacle. Each conductor has apparently 19 strands (seems like a funny number but I counted two different pieces). Looking at specs for lots of examples of this type of cord, it usually seems to have 41 strands (even stranger – maybe a few extra strands on the ‘hot’ side?). The cord’s usually called SPT-1 or -2 (depending on insulation thickness; there’s otherwise no difference) and also known as 18/2 (for the gauge of the overall wire and number of wires). Home Depot or Lowe’s will sell you a foot (30cm, 5 more than you need) – in my area for 28¢ / 37¢ respectively (wow, big difference!).

      Mine measures anywhere from 0.28 to 0.3mm at different points using good calipers and I see it generally spec’d at 0.3, which matches what we want here. (The above guess at 28AWG would be 0.321mm.) I am not sure all such cord has 0.3mm strands, but looking up about 5 mfgs specs online, and all either said 0.3mm explicitly, or had 41 strands and I assume that by sheer math that if the strands add up to 18ga they must be the right Ø individually.

      I’ll try to remember to come back and post results once I’ve tried it out, but I can’t think of why it wouldn’t be ideal.

      • I’m guessing Canada too as they use they same type of plugs/receptacles and probably same cord types as it would make simple economic sense to share standards. Possibly same for Mexico/Central America.

      ** not to be confused with the type of zip cord used for speaker hookup – I tried a bunch of different sizes of that that I also had in the wiring “paw-through” bin and most were far too small – more like 0.17mm.

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