AWG wires rating AMPS

To get a good answer, you need to specify the size of the wire, its insulation, whether it is isolated or with other conductors (I assume free air means that, but not sure), and what country (in other words, which code) you're working in. There's something else you need to consider, but I can't find my NEC book.

The other factor would be single conductors or multiples, i.e. triplexed. All the necessary information is in the National Electrical Code.

What is the load -- jeez CR4 is getting really stupid questions -

And I' stupid enough to respond to them. Any simple chart wiil give this duse his answer. LAZY STUDENTS I think

You must specify insulation rating.

Std. NEC published ratings are for: 60C. 75C. 85C. 90C.Insulation @ 20C. ambient.

For a 70C. ambient you're into some serious derating.

http://www.powerstream.com/Wire_Size.htm

National Electric Code (US) has tables of "ampacity" ratings.

HAZKHOD,

The typical tables in the USA are from the National Electrical Code (NEC). For conductors rated up to 90ºC they are based on an ambient of 30ºC with derating factors for the higher temperatures you mention. For conductors with higher temperature ratings they are based on an ambient of 40ºC, so use in an ambient of 35ºC is not derated. As others have said, the type of insulation has an effect, because with increasing temperatures the insulation's maximum temperature can be exceeded more easily.

Your question seems to ask what the ampacity is per unit of cross-sectional area. Much to my surprise, when I did some calculations, I found that the ampacity correlates best with diameter, not area. As diameters increase, the ratio of these two increases modestly.

In free air, I suspect the limiting factor on ampacity is not the insulation (since physical separation of conductors is normally the method of choice for achieving electrical insulation), but is the loss of voltage over the distance the wires run and the increased sag and corrosion of the conductor as temperatures rise. I would therefore suggest that the upper conductor temperature limit is 200ºC (because conductors rated for higher temperatures normally are nickel plated).

Below is a table I made from the NEC tables' data and derating factors:

Dia. Ampacity for Insulation & amb. temp.

mm, 90@35 , 90@70, 200@40, 200@70, col4/col1

2.6 , 53, 32, 90, 81, 34.7

4.67 , 101, 61, 165, 148, 35.3

7.4 , 182, 110, 293, 264, 39.5

10.6 , 288, 174, 467, 420, 44.0

14.6 , 437, 264, ~725, ~650, ~49.6

25.4 , 821, 496, --, --, --

41.4, 1498, 905, --, --, --

For those in the USA, these were AWG 10, 6, 2, 2/0, 250mcm, 750mcm, 2000mcm. For metric sizes or sizes not listed, I think you can be fairly accurate by using the known diameter and doing linear interpolation from the final column's ratio of ampacity divided by diameter. Sorry for the format of the table--I have listed using comma's to separate the entries.

I hope this helps--JMM

Thank you very much for your support, actually my application of such wires isinside condensing units of central air conditioner, type of insulation is PVC 105 °C and we are facing some problems to accurately size the wire for such high surrounding ambient at severe operating conditions of our compressors speciallt during summer time at Gulf area some of the used wires were having heat up although our wires supplier AMPS rating are having ( as per their confirmation ) good safety margin.

You might look at wires rated for the appliance industry, if severe heat is a problem. They typically have silicone rubber insulation and some have an additional glass braid over that. The conductors are usually nickel plated, but may be available for an OEM without nickel plating.

Your wire vendor should be able to give you the allowable ampacity for the wires in your application. I think your wire type is AWM. Sorry I didn't have an ampacity and derating for your insulation of 105ºC. The NEC tables do not have a separate listing for your wire.

One caution when you go to higher temperature-rated wires. The limiting factor for ampacity can easily be the point where the wires are terminated. Although the wire is rated and installed where it can easily shed its heat, at the terminal it is bringing some of this heat to the device it attaches onto. Therefore the allowable ampacity is often determined by the temperature rating of this termination.

In your work, it sounds like you also have to work with the limits and rules of the listing (approving) agency, such as Underwriters Laboratories (UL) or any of about 30-50 others in different parts of the world.

Regards--JMM

I'm no expert by any means, but the very upper limit for wires before they get considerably hot is 30 amps for 10 awg, 20amps for 12awg, 15amps for 14awg, 10amps for 16awg, and 5 amps for 18 awg... but at those levels the wiring will get quite warm. I guess those numbers are for short surges of power use, like motor start ups.

In warm environments I wouldn't put more than 1/2 to 2/3 of the current that I gave through the wiring for continuous use. From experience, putting more than that through the wires will give considerable voltage drops and very warm wires...

I don't understand why the current ratings for "chassis wiring" is so high (at that wire gauge link)... I know that putting 22 amps through 16 gauge wire will burn the insulation rather quickly! Even 8 amps through a foot of 16 gauge will get warm, and have a voltage drop of maybe 2 volts on a 12v dc circuit.

Not sure if I helped, but good luck.
Nick

where did you get those ratings that you listed?