# Calculating Ampacity On Different Materials

Discussion in 'General Electronics Chat' started by Andjeloti, May 17, 2007.

1. ### Andjeloti Thread Starter New Member

May 17, 2007
2
0
Hello,
I have often encountered the ability to calculate general ampacities for different sizes of conductors, primarily copper conductors.

What I am more certainly interested in is the ability to calculate for example a simple connector or a certain shape's ampacity, based on the material, i.e. copper, zinc, brass, etc. and its geometrical shape, resistivity or conductivity, and keeping in mind that it is done over a variable distance or length of the sample. Perhaps I am missing a few variables.

I have tried reasearching and looking up books on this idea but i haven't been able to draw positive conclusions, since most resources point in the direction of wire ampacities.

I really need help on this subject and I would most certainly be very thankful for any helpful information. And also, if there is any helpful books that I can aquire to be helpful with this sort of information i would be really thankful.

Thanks...

2. ### beenthere Retired Moderator

Apr 20, 2004
15,815
283
If you can calculate an accurate cross-sectional area of your conductor, you should be able to derrive the resistance. Ampacity has to do with temperature rise while carrying a stated current. There are published ampacity tables for copper conductors, based on standard wiring gauges.

Outside of copper and aluminium conductors, ampacity is going to be somewhat theoretical, unless you are just interested in finding a level of current that will cause the insulating materal to char, or the actual conductor to melt.

3. ### Andjeloti Thread Starter New Member

May 17, 2007
2
0
I am aware that with a cross-sectional area and a length of the conductive sample, i am able to determine the resistance of the material because resistivity values for a material are found in tables. But I am not quite familiar with calculation of ampacity since just like resistivity of a material it changes with temperature.

Once resistance of a material with its geometric shape, ex. a cube, is found at for example room temperature, how is ampacity determined at that same temperature?

The other question I have is, since there is standards describing maximum ampacity values for different size wires, is there certain standards that have to be met regarding ampacity of any type of material and its geometric form, an example a block of copper.

4. ### beenthere Retired Moderator

Apr 20, 2004
15,815
283
Consider the Wikipedia definition - http://en.wikipedia.org/wiki/Ampacity.

The concept is valid only when considering the safe limit for current in building wiring. Unless you are planning to draw zinc building wiring, then ampacity has no relevance.