current ratings of AWG cables

[joniengr081]

I found the following two links describing the current rating and resistances in the table for different AWG cables. 

I am wondering how they found the current rating for a given AWG cable ? The current rating would be different for single core and multi core cables ? Is that the maximum or peak current or continuous current ?

https://en.wikipedia.org/wiki/American_wire_gauge
https://www.powerstream.com/Wire_Size.htm

[wraper]

It is continuous current and is based on certain temperature increase over the ambient. It's not a hard rule and depends on the environment, if multiple wires carrying the current are packed together (worse cooling), type of insulation (say, silicon insulation hold higher temperature than PVC), etc...

[joniengr081]

You mean continuous current. So, the AWG 20 can withstand 11 A current continuous current ?

[Picuino]

Current is rarely all direct current, it usually has an alternating component.

In this case, DC current is also equivalent to RMS current.
For example, if a cable supports 10 amps of direct current, it will also support 32 amp pulses with a duty cycle of 10% (10.12 Amps RMS).

[perieanuo]

You can find current density tables for wires depending on wire technology and wire placement, electricians Bible. Ie,copper îs llike 7 amps per mm2 depending of wire instalation type (for example inside a wall into a tube) or in open space. It's more complex but the rules are there.
Br

[TimFox]

When comparing DC and AC:
Note that the "DC component" of the pulsed waveform above (32 A peak with duty factor of 10%) is 32 x (1/10) = 3.2 A, but the rms current is 32 x (1/10)^1/2 = 10.12 A (as stated by Picuino).
The "DC component" or mean value is what a typical DC ammeter would read for that current, but the rms value is what you use to calculate the power dissipation and therefore the temperature rise of the conductor.
(This assumes that the frequency is high enough compared with the characteristic time constants of the wiring and insulation.)
Of course, many "true rms" meters have a high-pass filter at the input that removes the DC component before measuring the rms value, so that waveform would read (10.12² - 3.2²)^1/2 = 9.6 A, which underestimates the heating.

[jonpaul]

Cable and wire ampacity Depends on RMS current (or DC if no AC is present), insulation rating, conduit, environment, open air, in chassis, buried etc.

See wire tables eg belden Wire and MWS Magnet Wire Supply

Use electricians forums like Mike Holt.

Jon

[calzap]

The usual goals for limiting ampacity of conductors are to not degrade the insulation thermally and to not damage surroundings by heat.  Achieving these goals requires consideration of composition of the conductor(s) … Al vs Cu for example … and diameter of conductors.  In addition, ambient temperature, insulation type, ventilation or other cooling, chemical environment, whether multiple conductors are in close proximity, and inductive heating of nearby wire coils and ferromagnetic materials must be considered.  Sometimes, other factors, like RF emissions, should be considered. There are no simple formulas or tables that can accurately provide useable ampacities of conductors based solely on diameter (e.g. AWG).

Various electrical code manuals and regulations have tables that take many of the above-mentioned factors into consideration.

Mike

[BlackICE]

I also consider power loss another factor to consider when choosing a wire gauge. For long runs even of the insulation and heat are within reason and meet code, you may not like the % power loss and or voltage drop.

[TimFox]

Also, it is typical for electrical codes for cables and portable cordage to mandate a maximum percentage voltage drop under load.
A typical spec:  The National Electrical Code says that a voltage drop of 5% at the furthest receptacle in a branch wiring circuit is passable for normal efficiency.