Electronics > Beginners

Buying wire

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msknight:
This is going to sound a bit bonkers, but... hey, this is the beginners section :-)

Previously, I have used wire I've stripped from various things for projects and stuff. No problem. I've got kynar wire for tracks, etc. but the majority of my hobby work has either been old car loudspeaker wire that I've got hanging around, or else I've stripped old cables and had no idea about what it's rated at. I find myself in the position where I'm building a game controller (yes, a joystick!) and I want to connect the LED's together, but I want to use something that I know is properly rated, not unnecessarily thick, and doesn't look like I've done a thoughtless scrap job on it.

The question is.... how do I go about buying wire?

I've done searches by voltage, trying to buy by amperage, and I'm getting flooded with search results which are not what I'm looking for. So... here I am.

I'm in the UK, so I'm presuming I'm buying by mm thickness rather than gauge? And is that by the included jacket or do I add a few mm to account for that as well?

Case in question this time is wiring joystick button LED's together. Only a few, 5V, total load will be around 100mA. I want something not too chunky as there's going to be a lot of wire in close proximity, but thick enough to do the job.

Or as I'm planning to buy a small reel for future use, perhaps something a little more highly rated?

Hoping for some education on buying wire before I lose more hair by trawling through e-bay.

msknight:
OK - to add a little to this...

I'm thinking of buying 10m of multi-colour 28 AWG ribbon cable and separating it into single strands which should... I believe... be 4 amps per strand ... but they say that it drops to about 1 amp, but I'm guessing that it's when its used as a ribbon cable and the problem is heat dissipation of the cables in close proximity.

Am I in the right ballpark? Am I understanding this right?

mindcrime:

--- Quote from: msknight on June 10, 2021, 02:51:39 pm ---I'm in the UK, so I'm presuming I'm buying by mm thickness rather than gauge?

--- End quote ---

Not necessarily. AIUI, the UK have their own "wire gauge" standard, which is similar to, but not exactly like, AWG (American Wire Gauge). So you might encounter that as well. And depending on what sites you're searching, it's entirely possible that you'll still encounter wire denoted using AWG. Of course you can probably choose to explicitly search only by mm diameter if you want, but I'd guess casual searches will turn up a mixture of different denotations. Not a big deal though, as finding conversion charts is pretty easy.



--- Quote ---Only a few, 5V, total load will be around 100mA. I want something not too chunky as there's going to be a lot of wire in close proximity, but thick enough to do the job.
--- End quote ---

If you know the current load you'll be dealing with, you can explicitly work out the required wire size. There are charts you can search up that show the current carrying capacity of various wire sizes. Or conversely, you can look up the resistance per unit of length for a given wire size and work it all out from there using Ohm's Law (assuming you know the expected voltage). The goal ultimately is to find the minimum required wire diameter / gauge.

Once you know that, you do have a few other choices to deal with, like insulation. But at 5V, any insulation is almost certainly going to be way more than sufficient. This starts to become more of an issue when you start messing with higher voltages and need to be very explicit that your wire is sufficiently insulated to deal with the voltage it's tasked to carry. Other than voltage rating, another factor to consider with insulation is its temperature resistance, and how supple it is. I doubt you're going to be pushing any temperature boundaries in this controller, so that's probably not a big issue. Just note the suggested max temp for your wire and double check that you don't be exposing the wire to anything above that. 

Silicone insulation is usually a very good combination of suppleness, voltage rating, and temperature capacity (which is why it's so often used for high quality test leads) but it's usually more expensive than some of the cheaper plastic insulating materials.

Also: note that in the above paragraph(s), I glossed over any reference to wire material. That's because, while various wire materials are available, I don't think there's any reason at all for you to consider anything other than copper wire for your application. But if for some crazy reason you did want to consider, say, aluminum wire (don't though), the charts I mentioned can be found where the wire material is one of the factors. But just use copper, really.

Stranded vs. solid core wire is another choice you'll need to make. Solid core usually has a little less resistance at a given size, and can sometimes be easier to connect to things without crimping or soldering on an explicit connector component of some sort. But stranded wire tends to be more supple and easier to work with. For an application like you're describing you could probably get by with either.

TimFox:

--- Quote from: msknight on June 10, 2021, 02:51:39 pm ---

The question is.... how do I go about buying wire?

I'm in the UK, so I'm presuming I'm buying by mm thickness rather than gauge? And is that by the included jacket or do I add a few mm to account for that as well?


--- End quote ---

Once, as an American doing an installation in the UK, the local guy asked if “4 mil” wire were adequate, and I thought he meant 4 mm diameter.  In fact, he meant 4 mm2, which is quite different.  I believe that wire in the UK is specified by the wire cross-section area (not including insulation).  The old British SWG was similar but not equal to the contemporary US AWG.

Zero999:

--- Quote from: TimFox on June 10, 2021, 03:32:14 pm ---
--- Quote from: msknight on June 10, 2021, 02:51:39 pm ---

The question is.... how do I go about buying wire?

I'm in the UK, so I'm presuming I'm buying by mm thickness rather than gauge? And is that by the included jacket or do I add a few mm to account for that as well?


--- End quote ---

Once, as an American doing an installation in the UK, the local guy asked if “4 mil” wire were adequate, and I thought he meant 4 mm diameter.  In fact, he meant 4 mm2, which is quite different.  I believe that wire in the UK is specified by the wire cross-section area (not including insulation).  The old British SWG was similar but not equal to the contemporary US AWG.

--- End quote ---
We use IEC 60228, which defines standard sizes by cross-sectional area. Unfortunately it only starts at 0.5mm2, so for smaller sizes AWG and occasionally SWG, or a rounded cross-sectional area close to either, is used insread. It would be nice if the IEC would go smaller, but I suppose there's less motivation to, as they're more concerned with big, hazardous electrical installations and equipment, rather than small stuff.

https://en.wikipedia.org/wiki/IEC_60228

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