Minimum wire size permissible?

Using Arduino General Electronics
1

Hi
I'm working on a consumer product and I'm trying to find out what the minimum permissible wire size for my application is. Looking at different AWG charts, I found it a little confusing and I'm not sure which values apply (power transmission or chassis wiring). Some people told me that I should take the value for power transmission but others suggested the value for chassis wiring. The wires need to be as flexible as possible, so I want to make sure that I don't use unnecessarily thick wires.

Here's the specifics. I will have a total of 5 wires bundled in one strand. 3 wires connect to a brushless motor that draws about .3-.4 amps @12V. The remaining two wires are connecting a battery (positive and negative) with a pcb board. They run 1.2 amps @12V. The length of the wires is ca 6-8inches. Insulation type is silicone.

Any input would be apprechiated.

2

Use the enclosure / chassis rating, remember flexibility is to do with the number
of strands more than the overall thickness. More finer strands are more flexible.

1.2A isn't much most wire will take that. Silicone insulated wire will take more as
it stands higher temperatures without damage, but hotter wires have more resistance
so there is a limit (your wire becomes a fuse instead).

I think the power transmission ratings are assuming lots of wires bundled in the same
conduit without ventilation, so are more conservative.

3

Power Transmission is for long distances. Chassis I think is under basically 3 ft or so? (Just a guess from my memory). Keep in mind that bundling wires together will decrease their capability due to heat, but it usually isn't a concern, as 22AWG wire is rated to 7A chassis current. You are probably okay with the 22AWG then.

4

Thanks for your replies. If chassis wiring applies, couldn't I even use 26 AWG wire? It has a chassis rating of 2.2 Amps which would give me plenty of overhead.

5

cordvision:
Thanks for your replies. If chassis wiring applies, couldn't I even use 26 AWG wire? It has a chassis rating of 2.2 Amps which would give me plenty of overhead.

Probably, but depending on the size of the product, it might be worthwhile to run something bigger just in case and never have to worry about it. You also don't know how large of current transients you'll experience, so leaving yourself lots of margin is nice and good practice. Also make sure to cover high enough voltage and temperature rating on the jacketting.

6

MarkT:
I think the power transmission ratings are assuming lots of wires bundled in the same
conduit without ventilation, so are more conservative.

The official rating charts are very conservative. They assume thick bundles of wires in places where heat can't escape.

OTOH it's a consumer product, better safe than sorry.

A good way to tell if you need thicker wire is to look at the voltage drop along it. If it's more than a few percent then you might need thicker wire.