A good AWG/current chart

[Sorrin]

Hey everyone,

I'm in the process of speccing out wire sizes. It seems like the chart found here: http://www.powerstream.com/Wire_Size.htm is the most popular chart I can find by googling around/searching these forums. However, the numbers here seem super conservative. 3.7A power for 16 AWG wire? That is crazy low.

Is there a better chart out there? Or a better way to tailor the chart to my(our) applications?

[Charles Kaneb]

"Power transmission" on that chart means transmitting power over large distances. Think "electrical grid". Calculate what the losses for 50 km of 16 AWG wire at 3.7A are.

Your application will be closer to the "chassis wiring" column - nothing on your car is more than three meters apart.

[EPMPaul]

Look up FAA AC43-13.1b.. Chapter 11. Gives you the slam dunk method to size wire.
It's an aeronautics method to size wire according to the FAA

[Warpspeed]

When deciding wire gauge there are two things you need to think about.
Total resistance and voltage drop, and temperature rise due to the current flow.

Very high temperature rated insulation can safely run higher continuous current than cheap crappy low melting point thermoplastic for a given conductor size.
That is why manufacturers rate their cables max continuous current differently.

For very long wire runs, voltage drop may be much more important than anything else, and you must run big gauge wire rated at far higher current than the current it actually has to carry.

[MCoach]

I made a chart based on FAA specs about a year ago.

We ended up running 30AWG wire to our dash. Had to pull apart some ribbon wire to get it, but it worked.

I wouldn't recommend that because you run into problems with actually running wire that small and it just breaking from vibration.

[Drew Price]

Terminating very small wires is a pain as well, another thing to keep in mind, especially for quick field repairs (30AWG will probably slide right out of red butt splice connectors for example).

Strain relief also becomes more important.

[Warpspeed]

There comes a point of diminishing returns where weight saving becomes ridiculous.
Ultra fragile wiring is not going to do you any favors.

Heat shrink tubing and zip ties can help prevent fatigue at the termination points, as can the rubber boots fitted to many types of plug.

[TMichaels]

With so many teams having electrical gremlins at comp every year, I also would not recommend to go down to 30AWG. It decreases reliability without a mentionable benefit.

Regarding general sizing:
Remember that all available charts usually refer to carrying the respective current for 24h and a high ambient temperature, usually 85°C or 105°C.
Now compare that to the use-case in an FSAE car...the tank/battery is empty after 30mins, which provides some cool-off time for the wiring.
Additionally, as said before: Keeping the wiring that carries much current short certainly helps and allows for quite some downsizing.

[murpia]

Where I work we have the opportunity to specify connector types & wire sizes for projects, including race cars using Deutsch Autosport connectors.

We have made it a policy to never specify smaller than 22AWG, for 2 reasons:

mechanical durability
ease of manufacture, service and rework

The weight saved by going < 22AWG is not worth the risk & inconvenience to us. I have seen some badly stretched and mangled harnesses that just kept on working at 22AWG.

Regards, Ian

[MCoach]

Originally posted by TMichaels:
With so many teams having electrical gremlins at comp every year, I also would not recommend to go down to 30AWG. It decreases reliability without a mentionable benefit.

Regarding general sizing:
Remember that all available charts usually refer to carrying the respective current for 24h and a high ambient temperature, usually 85°C or 105°C.
Now compare that to the use-case in an FSAE car...the tank/battery is empty after 30mins, which provides some cool-off time for the wiring.
Additionally, as said before: Keeping the wiring that carries much current short certainly helps and allows for quite some downsizing.

Yeah, it just wasn't worth the effort.
Just for everyone's reference, I don't run anything smaller than 24AWG nor anything larger than 10 AWG.

[EPMPaul]

Yeah the aeronautics stuff also has some part duty charts in there. As for weight of the wiring I did a quick MATLAB script to evaluate it and the wiring is something like 500g ( I range from 10AWG to 20AWG). Of course the associated connector pins etc are probably another 2-300g but not exactly gonna save kgs on your wiring unless you re running some serious DAQ 24-7.

Either way, just gives you an idea. Cute thing about the aeronautics standards are all the workmanship standards.

Not saying they re gospel, but they do give you a decent idea of how to go about making a wiring loom. Another good reference is this (http://www.liberatedmanuals.com/TM-1-1500-323-24-1.pdf) . Goes a little bit more into workmanship, crimping tools. Might be a little overkill but seeing how many cars fail because of wiring, overkill might not be such a bad thing.