# conductor rating

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given the required current rating of a conductor, how do you go about determining the required cross section of the conductor. Any documents would be great.

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you can search "wire gauge size" and find any number of tables or calculators. for example

different tables would apply if the conductor is in a metal conduit or subject to heat. aluminum wire uses a different table then copper.

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| given the required current rating of a conductor, how do you go about | determining the required cross section of the conductor. Any documents would | be great.

Cross section alone does not determine the current capacity rating of a given wire size. While you will see resistance being inversely proportional to the cross section area, consideration needs to be given to thermodynamics (the course that often makes or breaks engineers in school). Voltage drop across resistance means power dissipated as heat. But the heat must be removed. Unfortunately, wire cross section increases faster (squared) than the outer surface area (unless it is a hollow wire). At power frequencies for most cases, there is no skin effect, so the heat will come from the inside parts of the wire as well as the outside. Stranded wire will boost the outer surface area a bit. Then you have to consider the insulation. It will slow the heat dissipation rate (more so for thicker insulation required on higehr voltage wires), as well as being a limitation on the permissible heat rise. The ambient temperature is also an issue. And this gets more complicated with other heat dissipating conductors close by, especially if inside a cable sheath or conduit.

If you are an engineer, this should all be recalled/researched from that thermodynamics perspective. If you are an electrician, your training in sizing and load calculations should give the information you need. But if you are a hobbyist, or do-it-yourself-er, your best bet is to be rather conservative and overrate for safety, after finding out the basics of what sizes can carry what (and don't stuff many wires together).

It's simpler in most cases to just look up the capacity ratings in the tables in the National Electrical Code (for USA) or your Austrailian equivalent. There will also be some rules, particularly for smaller more common conductor sizes, that just spell out a maximum current that may be used. I can cite some of these from memory for US standard wire gauges, but since you are down under, you are likely using different wire size standards which would likely have different size points to consider.

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I just finished two calculators that do the job according to the 2005 NEC. I have about 2000 hours into building these programs and they are more accurate and better than WireGuide 2005 that sells for \$200 and mine are free and run in a webpage using JavaScript. They were proof tested using Internet Explorer version 6.0.

They are at:

Look in the data or voltage drop section for CMA.

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Actually the Neher MCgrath and Rosch heat transfer equations were used to develop the NEC Ampacity Tables. I worked about 400 hours writing an article on this in 1996. It is at

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develop the NEC Ampacity Tables.

I worked about 400 hours writing

The old adage fits here: "Those who Can ...Do "Those who Can't...Teach

But in Newton's case; he will try to con his way through everything, including this group. Here is a thread in the other group where he lies through his teeth, but unfortunately for Newton, it is filled with "Real Professionals", who called him out, yet again.

Thread on the Delusional Liar-Gerald Newton-Aka "Electrician@Electrician"

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The australian Equivelent-- AS/NZS 3000:2000 Electrical installations (known as the Australian/New Zealand Wiring Rules)

-- John G

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Electercian wrote:

I worked about 400 hours writing an article on this in 1996. =A0It is at