AWG size charts

[ccarrington]

Hi Guys,

Ok, my inspections are a little slow between the holidays and so have time to market and produce little educational displays for my clients. I had read somewhere before that securing different wires sizes to a board… with wires most likely to be found in residential systems was a good idea, so I did just that.

Now my discovery:

I purchased 1 foot chunks of all the main wire sizes from my local Home Depot, and miked them out with my micrometer (accurate down to .001). I discovered that 100% of wires are actually 1 gauge larger than is printed on the side. For example wiring sold as 3/0 is actually 4/0 as gauged by the micrometer, and for a second example 8 AWG actually miked to 7 AWG @ 0.14 inches per the charts… and so on and so fourth. Has anyone else discovered this or know this?

My question now is why? Is this because the wire manufactures are providing a margin of safety in their advertised wire sizes to account for bends and kinks and such? I understand there is not suppose to be an appreciable difference in current flow between stranded and solid wire (except over very long runs not normally found in residential electrical systems). The solid core GEC / ground wiring miked exactly true to gauge…

Anybody have ideas?

[Michael R. Boyett]

Were you measuring the wire or the wire/insulation?

[ccarrington]

No, I measured the copper conductor effective Dia...

[Michael R. Boyett]

I don't know then....let's see what the sparky's say.

[jclark1]

It's because of the way the strands are wrapped around each other.

[Paul W. Abernathy]

Hmm...probably best addressed to the manufacturers of the wire itself...While some sparky's may know this..I do not.....because actually I have never had a desire to measure this...WHY..

1.) Because the local AHJ is going to go by the Manufactures listing on the actual wire itself...not what I might measure with a device....

Much like they are not going to measure if a Ground Rod is 25 OHMS or less....they will just say put in (2) and be done with it....and oh yeah keep them 6 feet apart...

So...to be honest with you..I am sure panels also can handle more than their listed application but the manufactures list them for the intent....so I would say it could be a safety built in factor..and if it is..I LIKE IT....

Greg or Joe may have more on this...again the NEC does not address this issue other than the listing size on the conductor.....and well neither will the local AHJ......is it possibly you had COMPACT conductors and how they are wrapped...they may be slightly smaller....not sure.......anyway I would stick to the actual listing on the conductor itself and let that be the guide..no sense in making a confusing topic more confusing for the people learning from this educational display you are making...

Just my opinion from an Educator....

[ccarrington]

Paul I fully agree with you.

I think the wire is labeled as AWG XX but is probably sized a gauge larger for a liability /safety margin. I like that. I only miked the wires because I was bored and got curious…

On my display I list the wire size indicated on the wire, and it’s generally accepted amperage per my code check booklet.

[Greg Fretwell]

You were looking at the solid wire size in your chart. Table 8 shows #8 as .146 in.

[jtedesco1]

Here's Table 8 from the 2005 NEC