Spec 55 vs M22759/32: Same Wire, Two Names Explained
Happens at the counter every week. Bloke rings up, says his tuner told him to wire the whole car in Spec 55, and asks if we stock it. We do. It's sitting on the shelf marked M22759/32, and the printing on the insulation says M22759/32 too, and about half the time that answer starts an argument.
So let's settle it.
Two Names, One Reel of Wire
Spec 55 is a brand name. It belongs to TE Connectivity's Raychem division, and it covers their family of thin wall cross linked ETFE wires. The one you care about, the 55A0111 series, is manufactured to a US military specification called M22759/32. That spec sheet dictates the tin plated copper conductor, the insulation, the wall thickness, the 600 volt rating and the 150 degree ceiling.
Which means any manufacturer building wire to that slash sheet is making the same product. Raychem got there first and owned the professional motorsport supply chain for so long that their name became the generic word. Paracetamol and Panadol. Vacuum cleaner and Hoover. Your tuner says Spec 55 because his mentor said Spec 55, and the wire itself couldn't care less what you call it.
There's a third name floating around too. Tefzel. That one's DuPont's, and it's the brand name of the ETFE plastic the insulation is made from, not the wire. So the plastic is Tefzel, the spec is M22759/32, the famous brand is Spec 55, and when you walk into a wiring shop anywhere in Australia, all three words land on the same reel.
The Bit That Actually Catches People Out
Here's the trap, and it's the reason the pedants in the forums aren't entirely wrong to be pedantic. A handful of professionals use "Spec 55" to mean a different slash sheet altogether, M22759/44. Same cross linked ETFE insulation. Different conductor. The /44 runs silver plated copper instead of tin, and that buys it a 200 degree rating instead of 150.
| Specification | Conductor | Temp Rating | Where It Belongs |
|---|---|---|---|
| M22759/32 | Tin plated copper | 150 degrees C | ECU harnesses, sensor wiring, basically the whole car |
| M22759/44 | Silver plated copper | 200 degrees C | Sustained heat right next to exhausts and turbos |
Do you need the silver stuff? Almost certainly not. A properly designed harness gets routed away from exhaust heat in the first place, which is why the /32 covers virtually every circuit on a race car. If a build sheet genuinely wants the 200 degree wire it'll say /44 or silver plated in writing, not just Spec 55. If you're staring at paperwork and you're not sure which one it means, ask whoever wrote it. Takes two minutes and saves an expensive re-order.
Why Everyone Specs It Anyway
Put a length of M22759/32 next to the TXL you'd buy at an auto parts chain and the difference is obvious before you strip either of them. The mil spec wire is noticeably thinner and lighter for the same gauge. It doesn't melt back when the soldering iron gets close. Fuel and oil don't bother it. And it takes the vibration and heat cycles of an engine bay for years, which is the part PVC insulated wire quietly fails at.
It's aerospace wire construction, full stop. That's why the pros won't run anything else, and why we wrote a whole separate piece on it: why Tefzel wire is the gold standard for motorsport wiring in Australia.
Getting It In Australia
We keep genuine M22759/32 on the shelf in Melbourne and cut it by the metre, no minimum. Gauges run from 22 AWG for your sensor and signal work through 20, 18, 16 and 14 up to 12 AWG for the main feeds, in a proper colour range. Need shielded for crank triggers or CAN? That's M27500, same conductor family inside a tinned braid.
Check the insulation when your order lands. The military part number is printed straight down the wire, so what you paid for is verifiable at a glance. It's the same wire we pull off the same shelf for our own harness builds.
Frequently Asked Questions
Is Spec 55 the same as M22759/32?
For motorsport work, yes. Spec 55 is TE Raychem's product name and their 55A0111 series is made to the M22759/32 specification. Same conductor, same cross linked ETFE insulation, same ratings.
Where can I buy Spec 55 wire in Australia?
12Volt Motorsports stocks M22759/32 Tefzel wire, the wire the trade calls Spec 55, by the metre in Melbourne. 12 to 22 AWG, wide colour range, shipped Australia-wide.
What is the difference between M22759/32 and M22759/44?
Both use cross linked ETFE insulation. The /32 has tin plated copper and is rated 150 degrees C. The /44 has silver plated copper and is rated 200 degrees C for sustained high heat zones. Most ECU harness circuits belong in /32.
Is Tefzel the same thing as Spec 55?
Tefzel is the brand name of the ETFE insulation plastic. Spec 55 is TE Raychem's name for their wire family that uses it. M22759/32 is the military spec the wire is built to. In an Australian workshop all three names point at the same reel.
Why do build sheets say Spec 55 instead of M22759/32?
Habit. Raychem's branding stuck in the professional wiring world the way Panadol stuck for paracetamol. If the paperwork says Spec 55, M22759/32 is the wire it means.
Still not sure what your build sheet is asking for? Call 0458 102 134 or email 12voltmotorsports@gmail.com and we'll sort the wire list with you.