Determining wire length

[Rv8bill]

Hoping someone can add some clarity. How is each wire size determined when smaller wires are connected to a larger wire and the wires are different lengths? E.g. A Landing light in each wingtip draws 7.5 amps. Wiring from each light is 12' long and terminates in the center of the fuselage, where they connect with a single 5' wire going to the switch. Total current draw is 15 amps. The single wire from the junction to the switch is obviously carrying twice the load. A single point ground will of course mean the ground wires will be of nearly identical length as their power counterparts. I can see a couple ways of doing this. Curious to know how others have done it.

[Mike S]

You would benefit from getting a copy of The Aeroelectric Connection. It gives all the needed info you are asking about.

http://www.aeroelectric.com/

I would ground locally for the wing tip lights----done it in the past and no problems.

[rapid_ascent]

I think you have answered your own question. Each wire has to be sized for the current it is carrying and the length it needs to travel. For my strobes for example I have a common terminal strip where all the wing and tail lights join. The current is then effectively combined and then those wires carrying the combined current have to be sized for that current. In my case I used AWG 20 for each separate circuit and AWG 18 for the combined.

The problem with this type of approach would be if the combined current is high enough such that you need a breaker that is rated higher the breaker rating for the smaller size wire. Then you could potentially have a short on one of the smaller wires and the breaker not pop. As long as the breaker is sized below the rating of the smaller wire you should be good.

[Freemasm]

As described, my understanding is your system isn’t adequately protected. The wire gage requirements are the easy part. There are numerous nomographs available that will provide an easy answer based on amps, length, bundled/free air, etc.
Breaker(s) or fuse)s) are sized to protect the wire, not the device. You can replace the branch wires with an appropriate gage or reference the aforementioned book and install a fusible link as minimum or temporary configuration in the branches. Other choices but would require more rework IMO. If I’m misunderstanding your configuration/question, some of the very talented sparkles here will interject.

[PaulvS]

I am planning to run a separate power wire for each wing tip light back to the panel and a wig-wag lighting controller. Wig-wag is a good safety feature as it helps to be seen.

[Mike S]

Originally Posted by PaulvS

I am planning to run a separate power wire for each wing tip light back to the panel and a wig-wag lighting controller. Wig-wag is a good safety feature as it helps to be seen.

I assume you are using the Flyleds setup?? This is what I used in the new plane, and I highly recommend them.

The WigWag switch is something new, looks like a great unit. I used the module located behind the seat, fed from a panel mounted rocker switch.

[Desert Rat]

The easiest thing to do is size all the wires for the total load which allows you to run them through one appropriate sized breaker. Not the lightest, but certainly the simplest both to fabricate and to troubleshoot on down the road.

[PaulvS]

Originally Posted by Mike S

I assume you are using the Flyleds setup?? This is what I used in the new plane, and I highly recommend them.

The WigWag switch is something new, looks like a great unit. I used the module located behind the seat, fed from a panel mounted rocker switch.

Yep, I'm using the Flyleds setup. Mine is a 2-seater and the flasher module will be mounted on the sub-panel, hence the need to run a separate wire to each wing tip LED light. It's straightforward to size each of the wires and I think FlyLeds give some guidelines anyway.