broderp

Just general question for any electrical folks on the forum.


EXAMPLE:
A 20A DC circuit according to many sources requires a wire gauge of between 18 to 12 (based on wire length between 3 and 20 feet).


However I rarely see this when looking in actual car circuits. It seems like the wire gauge I find is much less than this. For example, power locks require a 20A circuit breaker, yet the wire is not 16-14 gauge wire.

So the question is what is wire gauge based on? Continuous load? (Power locks are not designed to be powered on continuously) or is there a general rule of thumb regarding average vs. peak load? Is the wirer truly 16-14 gauge (based on the below chart below) and my perception of the gauge is off?

The below images are typical of what I find. (Tessco technologies website)

Trailbreak74

Sooooo you want to discuss the factory wire harness? I'm sure the engineers at Ford did the math on that one. I wouldn't be interested in second guessing that.

Or did you want to discuss aftermarket wiring? I'm sure plenty of people cut corners when it comes to that. Thanks for posting the chart, it's a good guideline to use.

gone postal

Power locks require a large breaker in relation to wire size because it's a high momentary load through a coil (low resistance, high amperage) as opposed to a continuous load such as a blower motor.

LastResort

The circuit breaker should have a time/current characteristic that allows for the inrush of solenoid while still protecting a wire. The amount of current running through the wire is limited to the thermal capacity of the insulation and tolerable temperature rise.

In short, they've probably made engineering judgment to size the wire based on their knowledge of the materials in use, vs. typically available information that covers almost all circumstance.

broderp

I'm sure Ford did the math. I was more curious as to how they may have come up with the gauge wire they did as it does not seem to match what I see in the charts and graphs I find.

My intent was to do research on the topic as I am adding power locks this week to my truck. I'm heading out tomorrow to buy wire to bring 12VDC from my battery to the inside of the truck. I bought a fuse block:

but can't see running super heavy gauge wire as Ford also did not seem to have the need to do so. I'll later be adding power windows and power rear view mirrors in the spring or summer of next year. This fall will be the power locks and remote start.

Your welcome for the chart, glad it may help.


This makes sense, and was my thought as well. Thanks for supporting that thought. The actuators are not a continuous load.

So to meet manufacturing requirements, a cost point, as well as a certain safety margin, a smaller gauge wire can readily carry a momentary load safely as long as it's fused in a manor that can support the inrush current.

So in short, smaller gauge wire with a larger fuse.

I suppose I can run a 10-12 AWG wire from the battery to my fuse block, from there I can use maybe the wire gauge that is coming with my power lock kit.