How much current can it carry a 18 awg wire and a 20 awg?

[SparkyChem]

I am confused exactly on the maximum current capacity of these wires, assuming the typical copper wire. Google says for the 18 AWG that it is 16 amps. But it doesn't seem right. How about for 20 AWG and for 22 AWG?. Again Google says it is about 10 amps for the 20 awg for which it mentions that it also depends on the insulator?, and
well I couldn't find an specific google entry for 22 AWG, other than just stating that it will carry 0.92 amps, while this entry states that it can carry up to 10 amps. So I am confused.
Could any of these be used for an application which uses about 4 amps of current?. Let's say an extension for a small laptop such as the NB505? I am lost here, it would be nice if someone could explain me better how to understand the AWG table. Any help on this matter please?

 

[BradtheRad]

Link to useful table of wire gauges and ampacity ratings:

amasci.com/tesla/wire1.html

For 18 AWG it recommends max Amperes =3.2

20 AWG, 2.0 A

22 AWG, 1.28 A

Reduce Amperage if wires are packed (wound) around a core.

 

[Externet]

Pass a current on to your 20AWG wire, be it insulated, in conduit, buried, bare, bundled, summer, windy or snowy. Measure its temperature. You do not want it warmer? Then that is the maximum. Can you have it warmer without deforming its insulation or affect anything next to it ? Then increase the current until you measure that warmth is enough. That is its maximum current for you. (You select how hot you want it to work)

Do not like the method ? Check tables like ----> http://www.standard-wire.com/current_carying_capacity_copper.html for the proper environment.

 

[barry]

As alluded to in the previous post, current capacity depends on more than just the gauge. If you actually read the wire tables, it specifies current capacity for a SPECIFIC TEMPERATURE. That's why Teflon insulated wire has a higher rating than PVC.

 

[dick_freebird]

Rated current also varies with the environment. Wire in conduit is "still air" (especially non-metallic tubing) and wire in/on a bed of fiberglass attic insulation nearly so.

You might find useful tables at NEMA or various wire mfrs that incorporate the insulation material and thickness, but be sure to read the fine print.

 

[c_mitra]

I am confused exactly on the maximum current capacity of these wires, assuming the typical copper wire. Google says for the 18 AWG that it is 16 amps. But it doesn't seem right. How about for 20 AWG and for 22 AWG?. Again Google says it is about 10 amps for the 20 awg for which it mentions that it also depends on the insulator?, and
well I couldn't find an specific google entry for 22 AWG, other than just stating that it will carry 0.92 amps, while this entry states that it can carry up to 10 amps. So I am confused.
Could any of these be used for an application which uses about 4 amps of current?. Let's say an extension for a small laptop such as the NB505? I am lost here, it would be nice if someone could explain me better how to understand the AWG table. Any help on this matter please?

Surely you have now discovered that the maximum current capacity of a copper conductor is an elusive concept.

To answer your question, yes, you can happily use 20AWG wire for your laptop extension cord. If you voltage is 220V, the current will be less than 4A and most of the chargers does not mind some fluctuation (in the voltage). The charger will be a better source of information on the power input. If you are concerned about wastage of power in the extension cord, get a fatter extension cable.

The current ratings mentioned in the AWG tables is a rough guide worked out by wise men. What you should be worried that the core copper temp must not exceed 100C (from the ambient 25) because the insulation can melt. For motors and transformers, these values can be higher (the copper may be insulated with fiber glass and buried in a chunk of steel) but is a different case. You should use the resistance value and estimate the power dissipated by unit length of the conductor (also the enclosure).