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I couldn’t find a similar or duplicate question yet but regarding this table for instance a 24 AWG wire can carry max 3.5A current if it is single core. But if it is seven core it can only carry max 1.4A.

Am I interpreting the information wrong?

Is this table valid for DC current as well? What really creates such big difference with different number of cores of the same AWG cable?

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  • \$\begingroup\$ Guessing here. Multi-stranded wire with circular strands necessarily has air space between conductors. Copper is a very good thermal conductor; trapped air is an excellent thermal insulator. Perhaps the problem is getting the heat out to the surface of the wire, so that multi-strand wire runs hotter. \$\endgroup\$ – John Birckhead Jul 25 '19 at 19:06
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    \$\begingroup\$ @JohnBirckhead Multi-core in this sense does not mean multi-stranded. It just means combining multiple wires into a single cable to conduct multiple signals. In which case, it makes perfect sense why the ampacity would be decreased. \$\endgroup\$ – DKNguyen Jul 25 '19 at 19:18
  • \$\begingroup\$ To avoid confusion, I'd say that the referenced table refers to multi-conductor cables, not to an individual stranded wire. \$\endgroup\$ – Peter Bennett Jul 25 '19 at 19:28
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There are two points of confusion here:

  1. The difference between a CABLE vs a WIRE

  2. The difference between a CORE, STRAND, and CONDUCTOR

A wire is just the conductor (either solid or multi-stranded) and some insulation whereas a cable is the entire assembly of conductor or conductors, the insulation, shielding, jacket, armour, and tensile cord, etc.

Note, that wire and cable sometimes get used interchangeably.

A strand unambiguously refers to the components of conductive metal in a wire that that come together to conduct a single electrical current (whether one big strand or many strands twisted together).

A conductor unambiguously refers to the conglomeration of strands and each conductor conducts just a single electrical signal.

A core has ambiguous usage and may refer to a conductor or a strand. Core and strands also gets used interchangeably sometimes so it can get confusing. For example, I always say solid-core to refer to single-stranded, but I never say multi-core to refer to multi-stranded. I just say mult-stranded. I also say multi-conductor when referring the number of wires in a cable and have never heard the word core used until today but I knew what it was when I saw it. So yeah, it can get confusing if you're not familiar.

When someone says a cable is xAWG, it means that each conductor/wire in the cable is x AWG. It does not mean that the cable as a whole is that AWG.

This is single-strand (or solid-core), single-conductor cable: Alpha Wire Catalog]

This is mult-stranded (I have never heard this referred to as multi-core), single-conductor cable: Belden Catalog

This is solid-core, multi-conductor cable: Belden Catalog

This is multi-stranded, multi-conductor cable: Belden Catalog

Therefore, a multi-core cable is not the same as multi-stranded wire. A multi-core cable the conglomeration of multiple wires into the same cable so that multiple signals/currents can be conducted over the same cable.

Now the definitions are out of the way...you might ask: "Why does the ampacity decrease with more conductors/wires in a cable? After all, the resistance of each additional conductor/wire remains the same. If you double the number of conductors/wires, that halves the resistance of the cable. If you double the number of conductors, you double the ampacity of the cable."

Yes, adding more conductors/wires to a cable does increase the ampacity of the cable as a whole. And yes, doubling the number of conductors/wires also halves the resistance of the cable as a whole. And yes, the resistance of each additional conductor/wire added remains the same.

However, resistance is not the only thing that determines ampacity. Heat dissipation plays a role too and with more conductors/wires bundled close together, there not only less airflow and cooling that can occur, but extra heat sources around each individual conductor/wire. As a result, there are diminishing returns as you add more and more conductors/wires to a cable.

For example, a lone conductor/wire might carry 1A. But adding a second conductor/wire added might only add 0.9A of extra ampacity for a total of 1.8A. So the overall ampacity of the cable as a whole has increased from 1A to 1.8A, but the ampacity per conductor/wire has decreased from 1A to 0.9A.

From that perspective, it should make perfect sense why more conductors/wires in a cable reduces ampacity per conductor/wire, even as it increases the ampacity of the cable as a whole.

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  • \$\begingroup\$ Isnt core and strand same thing? \$\endgroup\$ – user16307 Jul 25 '19 at 19:24
  • \$\begingroup\$ @user16307 Core and strand can also get muddled just like wire and cable can in some cases. But notice that this text above and below the table tends to say cable rather than wire. It only uses wire when talking about individual conductors. \$\endgroup\$ – DKNguyen Jul 25 '19 at 19:26
  • \$\begingroup\$ Do you mean those cores are insulated from each other inside the same cable jacket? So when they say 3 core do they mean something like this?: en.m.wikipedia.org/wiki/Electrical_cable#/media/… \$\endgroup\$ – user16307 Jul 25 '19 at 19:28
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    \$\begingroup\$ "It makes perfect sense why the cable consisting of a bundle of wires would conduct less current since there is less airflow and more heat sources around the wire.", it doesn't make sense to me though. If you visualize them as resistors you should be able to double the current capacity if you have two cores since you halve the resistance. I don't know if it is physically possible to get worse conduction by adding conductors in parallel. - The 1.4 A OP is mentioning in his/her question must be per core. So a bundle of 7 -> 1.4*7 = 9.8 A, not 1.4 A. \$\endgroup\$ – Harry Svensson Jul 25 '19 at 19:33
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    \$\begingroup\$ @user16307 "No one carries in practice same current through multi core cable." You'd think so right? But alas, this is not true. \$\endgroup\$ – DKNguyen Jul 25 '19 at 20:33

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