16 AWG 252 strand ? - Page 1
Forum section: electronics / beginners

author: DW1961
author_rank: Frequent Contributor
timestamp: October 17, 2020, 06:58:06 am
content: I've been reading about wire and foudn thta stranded wire carries less current than solid. On this page, Engineering ToolBox, is a chart for wire gauge and types and the current they can carry.- search is the most efficient way to navigate the Engineering ToolBox!Engineering ToolBoxI recently received some silicon 16 AWG wire with a whopping 252 strands! The specifications say it can handle 12 Amps. That's 3 Amps less than solid core, according to the ET chart above. However, the ET chart also says that stranded wire with 43 and greater strands can only carry 5 amps. Then I see on another chart that 26 AWG stranded can carry 3.5 Amps.https://oscarliang.com/ctt/uploads/2014/05/wire-awg-amp-diameter-resistance-chart.jpgObviously there is more to current carrying capacity and stranded wire than the cart reflects. There must be different ways to bundle stranded wire. Obviously, this makes finding the right size wire frustrating. Can anyone shed some light on this for me, and how to go about doing it with so many different strands and bundling types?

author: Vovk_Z
author_rank: Super Contributor
timestamp: October 17, 2020, 07:15:42 am
content: I start from a question how flexible wire I need. The more flexible - more strands, and higher cost. Then I chose an AWG (square mm). But I have to say that almost always I use wire with some large or not but margin. And only for higher currents (>3..5 A) I may possibly choose a wire AWG without a margin when I don't want large thick wires.

author: DW1961
author_rank: Frequent Contributor
timestamp: October 17, 2020, 07:03:00 pm
content: Quote from: Vovk_Z on October 17, 2020, 07:15:42 amYeah, but how do you choose it based on the NON linear nature of current capacity? For instance, if you use solid core wire, then you have an easy job of decided which AWG to use, but when you move to stranded, the current capacities seems all over the place.

author: elekorsi
author_rank: Regular Contributor
timestamp: October 17, 2020, 08:54:51 pm
content: The biggest impacts on cable/wire current capacity are:-type of insulation (max permisible temperature)-enviroment conditions-number of current carying conductors in a cable/bundle-instalation conditions (free in air, behind insulation, etc.)Solid/stranded is not really the problem, at least in IEC standard as far as i know, it is not mentioned. Maybe i am wrong, as i use only stranded ones. Must check it tomorrow on my PC, too late now... I have no idea how it is with the UL.But current carry capacity is only one factor, you should also calculate what is you maximum alowable voltage drop...In general instalations also the short circuit currents are very inportant, to be able to properly select the oveecurrent protections.

author: TimFox
author_rank: Super Contributor
timestamp: October 17, 2020, 09:16:00 pm
content: Current rating of wires depends on (at least) these conditions. When comparing different tables, check that they are using the same conditions. National standards (US, EU) may differ.1. Allowable temperature rise (this depends on the insulation).2. Environment. Free air, bundled in cables, in conduit, transformer winding.As stated above, this is only a safety rating, to avoid fire, etc. For your application and wire length, you also need to consider the wire resistance. When you encounter an apparent discrepancy between different tables, you should take the conservative approach.

author: DW1961
author_rank: Frequent Contributor
timestamp: October 18, 2020, 04:32:52 am
content: Quote from: TimFox on October 17, 2020, 09:16:00 pmThe tables usually do give chassis vs transport. There needs to be a way to generally come to some idea of how much current a specific gauge of wire should tolerate. I suppose you could have an insulation that would allow the wire to turn so much current it would itself turn into molten copper, but that wouldn't be too great of a deal.Currently, I am generalizing that 22-26 AWG insulation wire will carry between 2-3.5 amps. Most of the pre built wires you get for computer LEDs are between 24-26 AWG. That's probably because they know the PC boards are limited to 2A and at most 3A each. The problem begins when you use an SATA powered LED hub, and so you are running a possible 6.5 Amps through that thing--MB current plus the SATA current of 4.5 Amps. Most of the time you have multiple lines coming off of the DLED hub, but I could see someone taking one prebuilt wire rated at 2 Amps, and running 6.5 Amps through it.I'm not too worried about it because I use the multiple wire approach. But it is feasible that people would run a single 26 AWG wire in a series or parallel for a total of 6.5 Amps. That's not going to end well.

author: TimFox
author_rank: Super Contributor
timestamp: October 18, 2020, 02:22:10 pm
content: The standard tables give you an idea of what thewirecan tolerate, without risk of fire. Those current values are well below what would cause the wire to act as a fuse (copper makes a lousy fuse due to its high thermal conductivity). As in most engineering, the real questions are in the details: obviously, one can tolerate a much larger voltage drop in a circuit energized by 120 V than in one energized by 3 V. If your application uses the 12 V supply in a motor vehicle, where the ambient temperature is relatively high, you should do a detailed analysis.

author: DW1961
author_rank: Frequent Contributor
timestamp: October 18, 2020, 06:21:44 pm
content: Quote from: TimFox on October 18, 2020, 02:22:10 pmI should have said "stranded wire." If you are using solid, then the tables are not confusing. It's when you use stranded the current recommendation is all over the place. As far as voltage drop goes, that's another question. I'm just concerned with current and stranded wire.

author: TimFox
author_rank: Super Contributor
timestamp: October 18, 2020, 07:51:12 pm
content: Look at the different sources and make a conservative choice.One detail about very fine stranded wire: assuming each strand is tin-plated, for a given overall diameter, the fine-strand bundle will have a larger fraction of cross-section area filled with tin, which has a higher resistivity than copper.The question “how much current can this wire carry” does not have a single answer, as a similar question about a semiconductor device or vacuum tube might have.

author: bill_c
author_rank: Regular Contributor
timestamp: October 18, 2020, 10:41:41 pm
content: https://en.wikipedia.org/wiki/American_wire_gaugeIt says "The AWG gauge of a stranded wire represents the sum of the cross-sectional areas of the individual strands" and the ampacity chart doesn't specify solid or stranded. In most cases, when the only difference is solid or stranded, the only difference should be slightly larger overall diameter for stranded. TimFox and others have good points also...

author: DW1961
author_rank: Frequent Contributor
timestamp: October 19, 2020, 05:40:08 pm
content: Quote from: bill_c on October 18, 2020, 10:41:41 pmYeah I saw that too. So you would think that more size would compensate for more strands.

author: tooki
author_rank: Super Contributor
timestamp: October 19, 2020, 10:38:52 pm
content: Huh? The size only matters for mechanical design. It’s the cross-sectional area (which AWG is a standard for) that matters. Stranded wire of a given gauge is thicker than solid because it is essentially partly air. I’m guessing that air between strands, being a thermal insulator, is why for a given gauge, solid wire is often rated as being able to carry more current, since it can sink the heat out better.The current rating basically relates to one thing only: temperature. (If temperature didn’t matter, we could run 10000 amps through 30 gauge wire. It’d be white hot like the sun, and it’d waste energy, but it would work.) But temperature does matter, so we need to a) ensure the conductor doesn’t melt, b) ensure the insulation doesn’t melt or burn off, and c) ensure the wire can’t cause anything else to catch on fire. The material and thickness of the insulation makes a huge difference in how much heat the insulation can handle. (And in turn, also affects how much heat the conductor can dissipate.)So when comparing wires, it’s not just the gauge that determines the current rating. It’s also the insulation.All things considered, wire is cheap, so we tend to err on the side of generously oversizing rather than bothering to calculate the exact thinnest wire we can get away with.