Shielded wire

[Tblack]

Only one problem, you are using the current for both strobe lights. There are separate wires going to the Lt. and Rt. strobes. The amps in each wire are going to be half of the total. If you run the calculator again using 4.9A you will find that you can use twice the length of wire previously calculated, and that 20 guage will work up to 27 feet.

We would agree if we wanted to put each light on it's own breaker, but the combined load at the breaker is still the peak draw of 9.9 Amps so a 10Amp breaker if we are powering them both on a single breaker. We don't feel comfortable putting a 10Amp breaker on a 20 Ga. conductor, if I'm thinking correctly the wire could overheat and
burn before the 10Amp breaker with trip.

[Tblack]

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Thank you for the lead, we will check with them.

[PapuaPilot]

We would agree if we wanted to put each light on it's own breaker, but the combined load at the breaker is still the peak draw of 9.9 Amps so a 10Amp breaker if we are powering them both on a single breaker. We don't feel comfortable putting a 10Amp breaker on a 20 Ga. conductor, if I'm thinking correctly the wire could overheat and
burn before the 10Amp breaker with trip.

Just trying to help. Your original question had to do with the gauge wire size, that's what I was answering. I will address CBs here too.

Using the stated 9.9A peak current means there are actually two 5A circuits going to the individual strobes. It is safe to use 20 gauge wiring, it can handle the 5A current for that length of wire per AC43-13.1B. Bottom line: You can save weight and readily obtain 20/4 shielded wiring.

But wait, there's more . . .
Regarding the CB: You are correct in not wanting to use a 10A breaker on 20 ga. wiring. If you choose to use 20 ga. wire you can use a 7.5A or smaller CB (see AC43.13-1B: Par. 11-51 and Table 11-3). Although the peak current is 9.9A for both strobes the AeroLed specs also show that the average current is 1.2A. This is what the CB is really feeling. A 5A CB would also work; it is both protecting the 20 ga. wiring, and provides 400% margin for the average current.

Still doubting?
I think the best way to explain the CB issue is to use an actual certified plane as an example. I maintain and train mechanics on the Daher/Quest Kodiak 100. Looking at the wiring diagrams I found the following. The Kodiak uses certified AeroLed NSP and SunBeacon strobes (apples to apples). They use a single 5A CB to feed two switches for the wing strobes (2 ea.) and flashing beacon. That means there are 3 strobes run through one 5A CB. The entire circuit uses 20 gauge wiring and the plane has a 45' wingspan (much longer wire runs then a Kitfox). The combined peak current for the 3 strobes is 11.5A, but the combined average current is only 1.4A. That is why they can use a 5A CB and 20 gauge wiring. Again, this is a FAA certified aircraft designed by aircraft engineers and approved by the FAA under the latest Part 23 certification standards.

Honestly, if you consider that one strobe circuit is only 0.6A you could safely use 22 ga. wiring. Actually the wire with most current is the ground because it grounds the nav and strobe; it would be 1.4A on that wire. Try running this number through the wire length calculator and see what length is acceptable.

Cheers!

[Tblack]

Phil,
Thank you for the great explanation, I wouldn’t have been concerned if the tech at aero yesterday hadn’t told me that we needed to use a 10A breaker. Using the Kodak for reference was a great idea. Aero doesn’t give a recommended breaker size in their data sheet that’s why I gave them a call. I’m all for using the lightest wire possible.
Regards

[PapuaPilot]

BTW welcome to the forum! I saw this was your first post on the forum and wanted to give you a proper answer.

Here is a copy of my wiring diagram for this circuit.


NSP.jpg

[Tblack]

Makes sense, used two breakers. Thanks for taking the time to post this.

[Delta Whisky]

Phil - a related, inquiring minds want to know, question (nothing to do with the nav/stobe light issue); specifically you said "It is safe to use 20 gauge wiring, it can handle the 5A current for that length of wire per AC43-13.1B." Why wouldn't you be able to use a 10A CB for two parallel circuits? (From your statement: "You are correct in not wanting to use a 10A breaker on 20 ga. wiring.") Thanks.

[PapuaPilot]

The problem is that a 10A CB is not protecting the wires, which a requirement in AC43.13-1B; it shows a 20 gauge wire must use a 7.5A CB (or smaller). If a circuit with a 20 ga. wire has a short and it doesn't blow the 10A breaker the wire can potentially overheating and cause a fire.

The circuit in the example I mentioned has 3 parallel circuits all on one 5A CB using 20 ga. wiring to all three strobes.

[Delta Whisky]

Thanks Phil - I appreciate your response. It did make me re-read the above postings and then get back into 43.13, and as painful as that can be, a good refresher.

I would add two points hoping that others might find helpful.

1. current calculation web sites often are for cars and assume a frame ground is being used. If return wires are used, the complete circuit length is to be used in the calculations/charts.
2. a small weight savings can be had when putting strobe, position, nav, and landing lights in wing tips by using a common ground but the total current in the ground wire has to be used when sizing.

BTW - there was a very good article in one of the aviation mags (either Kitplanes or Sport Aviation) only a month or two ago discussing ground returns; the considerations when torn between using wires or a chassis ground. (In full disclosure I'm a proponent of wires and a common ground buss.)

BTW (and this is an IMHO input) there are lots of automotive and marine wires that are as good as aviation wire for the intended use. They are supplied to one or more commercial specs which have to be read to determine usability in an aircraft. In all cases, wire used in an airplane has to be plated - raw copper like lots of the stuff off the selves in you see in the local BB store is no bueno. BUT (#1) - it is much easier buying to a milspec so this is a non-value added comment. But (#2) - if you are stuck between a rock and a hard spot . . . . . . . .

[Doggitz]

Phil

Nice drawing. What program did you use to generate the schematic?

Fred