Which “Automotive” Wire is right for you?

If you’re looking at buying wire for your automotive application there are a number of acronyms, and names you may have heard. In general the name of each wire relates to the insulation material, but whichever wire you go for, ensure that it uses a copper conductor and is of a sufficient size (if you’re unsure of sizing, check out our article about wire size).

Some of the common terms you may have heard are:

• PVC
• TXL
• Spec 44
• Tefzel/Spec 55

PVC

PVC wire covers a large range of wires, and is manufactured with varying tolerances. We generally avoid this type of sire despite it being one of the most commonly available and widely marketed as “automotive” wire. With a temperature maximum of 90^oC (some brands do a 105^oC range) it is generally unsuitable for automotive use.

When using heat shrink for either sheathing or booting, the low temperature rating means that the insulation can melt and the conductors can end up touching under the shrink causing problems.

On top of this, PVC wire commonly has very small conductors and a thick insulator, meaning much “larger” wiring for less actual current carrying capacity. Despite the thick insulation, the properties of the insulation means that it lacks the protection given by other much thinner insulation types, such as those used in the other wire types below.

TXL

TXL stands for Thin Wall Cross-Linked, and is a stranded single conductor copper wire with a cross-linked polyethylene insulation. TXL wire is abrasion, chemical, and stress crack resistant as well as being rated for use from -51^oC to +125^oC.

TXL is a large step up in quality from PVC and is generally the lowest tier of wire that we consider acceptable for use in an automotive application.

The low temperature rating can potentially cause issues when using DR-25 sheathing which has a recovery temperature of 175^oC, despite this a lot of people have had success with this combination. We generally avoid using DR-25 with this wire and would use braid to ensure no problems with insulation melting under the sheathing.

TXL
Wire Size (AWG)	CSA (mm2)	Nom. OD (mm)	Max Weight (g/m)
22	0.32	1.6	4
20	0.51	1.8	7
18	0.82	2	9
16	1.31	2.3	13
14	2.08	2.6	21
12	3.31	3.2	33
10	5.26	3.9	52

Spec 44

Spec 44 wire offers a major increase in performance for a negligible difference in price. With a tensile strength of 4000PSI and a -65^oC to +150^oC temperature rating Spec 44 wire is built tough. This is thanks to a dual wall construction which combines the outstanding physical and electrical characteristics of radiation crosslinked polyalkene with the excellent mechanical and chemical properties of radiation cross-linked polyvinylidene fluoride (PVDF).

The radiation crosslinking of the materials used in Spec 44 makes them nonmelting at high temperature. As a result Spec 44 wire is resistant to prolonged contact with solder irons and is resistant to current overloads which would melt most thermoplastic insulation.

The flexibility of Spec 44 makes it one of the easiest of the ‘high performance’ wires to install. Stripping is done with conventional die blade strippers. The tin-plated conductor is easily soldered or crimped. The insulation may be easily printed and does not need etching before potting.

All of these features may make the Spec 44 sound like it has a bulky and heavy insulation, after all, there are two layers to it. This is not the case though, as seen below, despite having a larger cross-sectional conductor area the Spec 44 is also thinner and lighter than the TXL for a given gauge.

Spec 44
Wire Size (AWG)	CSA (mm2)	Nom. OD (mm)	Max. Weight (g/m)
22	0.49	1.19	4.46
20	0.77	1.39	6.7
18	1.21	1.65	10.12
16	1.53	1.83	12.8
14	2.41	2.26	19.64
12	4.01	2.74	30.06
10	6.47	3.28	46.28

Overall the Spec 44 is a superior option, and in our real-world experiences performs far better than TXL. For this reason we Spec 44 wire is the lowest grade of wire that we sell as it is a product we can confidently stand behind.

Tefzel / Spec 55

Commonly known as Spec 55 and Tefzel, this wire’s part name is M22759 (catchy we know).

Spec 55 is a relatively small jump up compared to all the previous wires discussed, being very similar to spec 44 in a number of ways. Both of these wires have a -65^oC to +150^oC temperature rating and tin-coated copper conductors. There are some differences, with the spec 55 having a tensile strength of 5000PSI, and a single wall insulation.

Now is a great time to mention that Spec 55 actually comes in two varieties M22579/16 and M22579/32. Both have the same properties listed above, but have a difference in the insulation itself.

M22579/16 uses an Ethylene Tetrafluoroethylene copolymer (ETFE) insulation, and is roughly 15% larger than /32 and 20% heavier*.

M22579/32 uses a Fluoropolymer Cross-linked Modified Ethylene Tetrafluoroethylene copolymer (ETFE) insulation. This makes it roughly 15% smaller, and 20% lighter than /16.

*Comparisons based on 24ga.

Spec 55 was developed for high temperature airframe and avionics, its ETFE insulation has great resistance to high PH cleaning fluids, fuels, lubricating oils, and many other chemicals.

Being a single layer, the insulation is incredibly thin, but due to its robustness the risk of breaking through the insulation layer is low. Meaning you have a very small and lightweight wire, with more protection than some of the thicker insulations. This lightweight, heat and abrasion resistant wire is perfect for use in motorsport as it combines all of the best aspects of other wires in terms of size and mechanical properties.

One slight downside of Tefzel is that due to its mechanical toughness it can require specialized tools to work with. Particularly when stripping the wire, conventional strippers may struggle. We have had success using the Knipex 12 52 195 auto strippers.

As you can see below, the copper area of both the spec 44 and spec 55 are the same, with the spec 55 being a smaller and lighter wire due to its thinner insulation.

Tefzel
Wire Size (AWG)	CSA (mm2)	Nom. OD (mm)	Max. Weight (g/m)
22	0.49	1.09	4.17
20	0.77	1.27	6.4
18	1.21	1.52	9.67
16	1.53	1.73	12.35
14	2.41	2.16	19.35
12	4.01	2.62	29.32
10	6.47	3.25	47.32

Tefzel is another wire type we are proud to supply as we can be sure that it will be up to the task, and perform well. We supply the /32 variety.