OK so im a volunteer firefighter/emt. the installation manual for my lights says any customer supplied wire must be sized to supply at least 125% the max operating current. The max current is 390mA @13.6 VDC. What wire should I select? looking on radio shack i cant seem to find anything about mA rating on the hookup wiring products

 

It's about the properties of copper wire, versus the gauge of the wire (which is about the only thing you'll get out the Shack).

Any piece of copper wire will have a resistance, sometimes stated per 1000 feet. The limits on using that wire depend whether it's coiled up (so it cannot dissipate heat), how long it is (total voltage drop), acceptable voltage drop and other factors.

If you just need 390mA over a few feet or less, standard 22 gauge "hookup" wire should be fine. Larger (smaller gauge) is better. If it needs to withstand mechanical flexing, a stranded wire would be better.

 

Uh oh, I just re-read your post and realized this is probably a forbidden "automotive modification" topic.

 

It's almost impossible to buy wire too small for the current. It calculates to about 28 gauge. You are buying wire to survive the mechanical stress caused by vibration, friction, and tugging stresses. As long as you're plugging your lights into the cigar lighter, you are OK with the automotive ban. Start pulling cable out of the dashboard and we refuse to participate.

 

I second 22 AWG (or 20..or 18)
anything smaller (higher number = smaller wire) is just difficult to work with/breaks easily.

and yes 400mA = LOW current and basically any wire can handle that with ease.

 

edit: broke a rule sorry

 

edit: broke a rule sorry

In reality it shouldn't not really a broken rule because your asking about what kind of wire to use , not how to mod the vehicle but it might be a grey area ... Personal I would use what every gauge you have laying around because as long as you meet the min gauge and you can always use a bigger gauge and it won't affect anything and is good to have later down the road in case it has to power something else ..