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Current vs. wire gauge

Started by Peter Percival August 10, 2019
What current can 18AWG wire carry?  And, more usefully, is there a table 
somewhere giving this info for all the usual gauges?
Peter Percival wrote:
> What current can 18AWG wire carry?� And, more usefully, is there a table > somewhere giving this info for all the usual gauges?
To answer my own question - https://en.wikipedia.org/wiki/American_wire_gauge#Tables_of_AWG_wire_sizes 10A, apparently.
On 8/10/2019 6:51 AM, Peter Percival wrote:
> Peter Percival wrote: >> What current can 18AWG wire carry?  And, more usefully, is there a >> table somewhere giving this info for all the usual gauges? > > To answer my own question - > > https://en.wikipedia.org/wiki/American_wire_gauge#Tables_of_AWG_wire_sizes > > 10A, apparently. >
I'm a bit confused: that table has ampacity at 3 different temperatures (60, 75, & 90C) - does that mean that at the current given, the wire will heat to that temperature? If so, an insulation rating of 20C & ambient 30C (50C insulation rating) isn't consistent with the wire being 60, 75, or 90 is it? As I said: confused.
In article <qim7j8$ljs$1@news.albasani.net>, peterxpercival@hotmail.com 
says...
> > Peter Percival wrote: > > What current can 18AWG wire carry?&#2013266080; And, more usefully, is there a table > > somewhere giving this info for all the usual gauges? > > To answer my own question - > > https://en.wikipedia.org/wiki/American_wire_gauge#Tables_of_AWG_wire_sizes > > 10A, apparently. > > >
The current a wire can carry is really confusing. In open air a # 18 wire will melt with about 82 amps going through it. You may be able to put 70 amps through it, but it would probably burn your hand and melt most any insulation on it. One deciding factor is how much voltage drop do you want to allow in the wire. If you have a long run of wire, you surely would not want to run # 18 wire as the voltage drop would be very great. Another factor is if it is being used in a transformer where the heat build up is a deciding factor. If running several or more wires in a piece of conduit, the wire needs to be derated.
On 10/08/2019 9:27 pm, Bob Engelhardt wrote:
> On 8/10/2019 6:51 AM, Peter Percival wrote: >> Peter Percival wrote: >>> What current can 18AWG wire carry?&nbsp; And, more usefully, is there a >>> table somewhere giving this info for all the usual gauges? >> >> To answer my own question - >> >> https://en.wikipedia.org/wiki/American_wire_gauge#Tables_of_AWG_wire_sizes >> >> >> 10A, apparently. >> > > I'm a bit confused: that table has ampacity at 3 different temperatures > (60, 75, & 90C) - does that mean that at the current given, the wire > will heat to that temperature?&nbsp; If so, an insulation rating of 20C & > ambient 30C (50C insulation rating) isn't consistent with the wire being > 60, 75, or 90 is it?&nbsp; As I said: confused.
As heat increases so does the resistance and then of course the power dissipated rises, then the heat increases and so on. The derating is used for cables enclosed or in hot ambients etc.
On 8/10/2019 9:27 AM, Bob Engelhardt wrote:
> On 8/10/2019 6:51 AM, Peter Percival wrote: >> Peter Percival wrote: >>> What current can 18AWG wire carry?&nbsp; And, more usefully, is there a >>> table somewhere giving this info for all the usual gauges? >> >> To answer my own question - >> >> https://en.wikipedia.org/wiki/American_wire_gauge#Tables_of_AWG_wire_sizes >> >> >> 10A, apparently. >> > > I'm a bit confused: that table has ampacity at 3 different temperatures > (60, 75, & 90C)
Those numbers refer to the rating of the insulation on the conductor. The higher the temperature rating of the insulation the more current the conductor can carry safely.
> - does that mean that at the current given, the wire > will heat to that temperature?
No. It means that at the current specified in the table, the insulation will not break down.
> If so, an insulation rating of 20C
No such thing as an insulation rating as low as 20C for the wires in that table. 20C is roughly room temperature. Ed
On Sat, 10 Aug 2019 10:51:45 -0400, Ralph Mowery wrote:

> One deciding factor is how much voltage drop do you want to allow in the > wire. If you have a long run of wire, you surely would not want to run > # 18 wire as the voltage drop would be very great.
Yep, conductor length is often omitted, but still very important. You can get some crazy big currents to pass largely unhindered through very thin, short conductors. Fuses are a good example, come to think of it. -- This message may be freely reproduced without limit or charge only via the Usenet protocol. Reproduction in whole or part through other protocols, whether for profit or not, is conditional upon a charge of GBP10.00 per reproduction. Publication in this manner via non-Usenet protocols constitutes acceptance of this condition.
On 8/11/2019 2:31 AM, ehsjr wrote:
> On 8/10/2019 9:27 AM, Bob Engelhardt wrote: >> On 8/10/2019 6:51 AM, Peter Percival wrote:
...
>>> https://en.wikipedia.org/wiki/American_wire_gauge#Tables_of_AWG_wire_sizes
>> I'm a bit confused: that table has ampacity at 3 different >> temperatures (60, 75, & 90C) > > Those numbers refer to the rating of the insulation on the > conductor.&nbsp; The higher the temperature rating of the insulation > the more current the conductor can carry safely. > > >> - does that mean that at the current given, the wire will heat to that >> temperature? > > No. It means that at the current specified in the table, > the insulation will not break down. > >> If so, an insulation rating of 20C > > No such thing as an insulation rating as low as 20C for > the wires in that table.&nbsp; 20C is roughly room temperature. > > Ed
OK ... what you say makes perfect sense - it's the table that does not make sense. The column is titled: "Ampacity at 20&deg;C insulation material temperature rating,..." and a floating note assumes ambient of 30C. Then there are 3 columns titled 60C, 75C, & 90C. There must have been cutting and pasting to make the table, creating contradiction. Thanks, Bob