Wire Gauges and Shields

I've been taking a look at other professional harnesses as I start my project but I've noticed something that I've been struggling to comprehend. In a few of these harnesses I've noticed that they use all 20 or 22 gauge wiring for the entire engine loom... including the coils packs. How do you get away with using a 22 gauge wire to power a coil pack? My math and cross referencing the charts lead me to believe I should be using a 16 gauge wire with a Subaru coil pack that measures .72 ohms. I'm stumped.

Also, for shielded wires going through Deutsch Autosport connectors, do you just use solder sleeves with a lead going to a contact on either side of the connector? About how far back from the connector do you usually put those?

Hi Sam,

The professional looms that you would be looking at are most likely to be using a Tefzel or similar wire spec, this is done so that a smaller gauge wire can be used as a replacement for a larger gauge PVC coated wire that has the same load rating. There is also the expectation that the looms in race cars will be lifed, and that they do not need to survive for 25 years like a road car loom would need to.

With the shielded wires, that is an easy way of doing the shields, and it will work well if done correctly. You want to do the sleeving as close to the connector as possible, to minimise the amount of exposure the unshielded wires have.

Thanks BlackRex,

I delved a little further into it and yes, the secret is mostly in the wire. The charts you usually see for ampacity don't capture the whole picture especially since wires are rated by temperature (which Tefzel is typically in the 150C range compared to generic wire around 70C). The 22 gauge harness I mentioned was for a dedicated rally car that doesn't rev very high and relatively low boost compared to other applications where a thicker wire would be required. Just goes to show how important experience is.

Sam,

You may also find that the load ratings of wires are based on 100% duty cycle but coil or injector would not be achieving this so would generate less total current and temp.