This was taken from the Spitfire mailing list and is printed here with permission.

Last update: 05/23/1999

I would like to submit the following as a primer for the basics for wire on our LBC's. Most of this information is available through SAE specs.

I have found that many auto parts companies and some of the people that SHOULD know about wire don't know squat.

I sell wire for a living, Automotive, Appliance, ect. Some of you go to the local auto store and pick up a roll of whatever they have available to re-wire your project whatever it may be. Did you know that there is a big difference in automotive wire types? Knowledge is a good thing, as I have found, complete knowledge is a pipedream.. but I DO know THIS stuff! Let me preface all the following by telling you how to assertain the AWG of a wire.

First, take a small cut, about 1/2", remove the insulation, count the individual strands of the copper, use a mic and measure ONE strand. Count the number of total strands that you have. Then use the following to see what AWG of wire you have.

7/.028=20
16/.030=18
19/.029=16
19/.027=14
19/.025=12
19/.023=10
19/.021=8
37/.021=6

There are three distinct types of insulation on automotive wire. Extruded = GPT -40c to 80c Crosslinked = SXL,GXL,TXL ,-51c to 125c This was the standard for all automotive applications until about 5 years ago. This material is Crosslinked PVC, it's extruded through a tube under heat and pressure to "crosslink" or change the molecules of the insulation to another state.

GPT type, automotive Primary Wire. Thermoplastic; SAE-J1128

This insulation can be melted with a heat source, you can change the form with heat.

Most of your local-yokel autoparts houses sell the cheapest type of automotive wire available to them, the most common is what in the industry is called "GPT". The insulation on this wire is PVC usually a -40c to +80c. The wall thickness of this material is .023 from 20 AWG to 14 AWG. I have found that this is the standard for our LBC's. For those that have access to the SAE manuals it's SAE J-1128.

SXL type, automotive Primary Wire. SAE J-1128 This material is crosslinked PVC. Heat source will cause a "popcorn" effect to the wire. Insulation will not "melt" off wire. Wall thickness of insulation is:

20 AWG .029
18 AWG .30
16 AWG .032
14 AWG .035
12 AWG .037
10 AWG .041
8 AWG .043

GXL type, automotive Primary Wire. SAE J-1128 Same as above on heat. Wall thickness of insulation is:

20 AWG .023
18 AWG .023
16 AWG .023
14 AWG .023
12 AWG .026
10 AWG .031
8 AWG .037

TXL type, automotive Primary Wire. SAE J-1560 Same as above on heat. Wall thickness of insulation is:

20 AWG .016
18 AWG .016
16 AWG .016
14 AWG .016
12 AWG .016

I know this seems like a mess but if you have questions please call me @1 800/692-2323 Ext. 2105 or visit our web site, www.iewc.com

Craig Smith
800/692-2323 ext. 2105
fax 864/234-1020
craigs@iewc.com