The Murphy Builders Site

I'm trying to plan the installation of the wing wiring for
nav/strobe/position lights in the wingtips and am somewhat confused about
determining the appropriate wire size.

My intentions are to purchase the Aeroflash nav/strobe/pos lights and, with
that in mind, I emailed the company to ask their recommendation.

Aeroflash advised to use "18GA wire.......12 amps max so use a 15 AMP
breaker".

However, when using the tables in AC 43.13-1B, and using a wire length
'guess-timate' of 25 feet , a 12 volt system, and 12 amp circuit current,
the appropriate wire size is 10 AWG.

Could anybody shed some light?

Thanks

R. Hoffman #687R
Eugene, OR USA

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On 16 Feb 2001, at 8:02, Roger and Alice Hoffman wrote:

Aeroflash advised to use "18GA wire.......12 amps max so use a 15 AMP
breaker".

However, when using the tables in AC 43.13-1B, and using a wire length
'guess-timate' of 25 feet , a 12 volt system, and 12 amp circuit
current, the appropriate wire size is 10 AWG.

Depends on which side you're talking about. DC into the strobe
box, or the power to the strobe tube?

For the battery side, I suspect that the 12 amps is when the unit is
first turned on or just after the tube has fired. As the capacitors in
the unit charge, the current falls rather rapidly, so the average
current is less. (Assuming 12A is peak, not average.)

---
David Parrish

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In a message dated 2/16/01 10:04:30 AM Central Standard Time,
rognal@continet.com writes:

I'm trying to plan the installation of the wing wiring for
nav/strobe/position lights in the wingtips and am somewhat confused about
determining the appropriate wire size.

R. Hoffman
Check out [ www.catalog.com/susq/other/wiring.htm#chart ]
Phil&Lisa Smith #460

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Roger

The size of the wire must be thick enough so that it does not overheat.
Thicker wire heats less for a given current. Within reasonable limits,
average current is what is important to determine this. I think you have
a situation with a momentary peak 12 amp current which would require a
15 amp fuse but an average current that is maybe 3 amps. Thus 18 ga wire
is adequate from a heating point of view unless an equipment failure or
short occurs.

If you wade through all the references I suspect you may decide that a
15 amp fuse is OK but it is desireable to use a smaller perhaps 12 or 10
amp circuit breaker. It takes considerable overcurrent to trip a circuit
breaker quickly whereas a 15 amp fuse will open very quickly with even a
slight overcurrent. You should have a situation where with a dead short
on the end of the wire, the fuse or breaker will shutoff the power
before there is an overheat or fire risk. Perhaps a bigger risk though
is how hot will the wire get if there is a failure that draws say a
constant 13 amps on a circuit that is protected by a 15 amp breaker or
fuse. Sometimes that means that you should size up the wire or size down
the breaker, especially if the wire is enclosed in any kind of conduit
such as plastic hose that restricts wire cooling.

So yes, I agree with your concern and would personally not install a 15
amp breaker on 18 ga wire. This is only off the top of my head but it is
past my comfort level. You might want to consider one size heavier wire
and perhaps one size smaller breaker if using breakers.

FWIW
Ken

Roger and Alice Hoffman wrote:

I'm trying to plan the installation of the wing wiring for
nav/strobe/position lights in the wingtips and am somewhat confused about
determining the appropriate wire size.

My intentions are to purchase the Aeroflash nav/strobe/pos lights and, with
that in mind, I emailed the company to ask their recommendation.

Aeroflash advised to use "18GA wire.......12 amps max so use a 15 AMP
breaker".

However, when using the tables in AC 43.13-1B, and using a wire length
'guess-timate' of 25 feet , a 12 volt system, and 12 amp circuit current,
the appropriate wire size is 10 AWG.

Could anybody shed some light?

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Check out this article http://www.aeroelectric.com/articles/wiresize.pdf
on Bob Nuckolls AeroElectric Connection site.
http://www.aeroelectric.com/ Lots of good tips and instructions on
electrics.

--
Wray Thompson ...Rebel 306 ...home page http://wrayt.tripod.com/
My ICQ number is 29764664


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Roger and Alice,
I am installing the same position/strobe system that you are looking at although
there are different options for the strobe power supply. The A600-PG and PR light
assembly has the following current requirments(you should double check these with Whelen
but these are the figures given in my Whelen installation package):
- for each side At 14 volts, the forward position light draws1.9 amps and the tail
position light draws 1.8 amps this adds up to 3.7 amps per side for the position lights a
total of 7.4 for both sides.
-the A413A HDA power supply provides power ONLY to the strobes and it draws 7 amps
Typically you will switch the position lights seperately from the strobes. A seperate
circuit for the position lights needs to be able to supply the 7.4 amps for their
operation.
The breaker or fuse that you use is sized to protect the WIRE that supplies the
appliance not the appliance itself. Look at Figure 11.1 in AC43.13. It recommends a
maximum 10 amp breaker or fuse for 18 gauge wire. I installed 16 ga wire in the wings
for the position lights and will use a separate 10 amp FUSED circuit. (see
www.aeroelectric.com and buy his book you will need it if you intend on doing your own
wiring). According to AC43, 18 ga could have been used.
A seperate circuit to power up the strobe power supply will need to supply the A413A
HDA power supply with 7 amps. This is not crutial at this point as you are only putting
wires in the wing. I will use 16 ga wire for its power with a 10 amp FUSE.
I purchased the Whelen installation wiring kit for the strobes. These are the wires
that will fire the strobes and run from the power supply to the lights mounted in the
wing. This is a 1/4" dia wire bundle with the 3 sheilded wires for the strobes only. Just
buy it and install it. I cut mine in half and installed one half in each wing. I think it
is 60 feet long to start. This simplifies your decision for strobe wire sizing.

Disclaimer: These are design features that are used in my experimental aircraft and you
must review and verify all numbers with appropriate sources. These numbers and features
are being provided to share my experiences with others and are not intended to direct
anyone in the design and manufacture of their experimental aircraft.

I hope this helps,
Good luck,
Rick D.


Roger and Alice Hoffman wrote:

I'm trying to plan the installation of the wing wiring for
nav/strobe/position lights in the wingtips and am somewhat confused about
determining the appropriate wire size.

My intentions are to purchase the Aeroflash nav/strobe/pos lights and, with
that in mind, I emailed the company to ask their recommendation.

Aeroflash advised to use "18GA wire.......12 amps max so use a 15 AMP
breaker".

However, when using the tables in AC 43.13-1B, and using a wire length
'guess-timate' of 25 feet , a 12 volt system, and 12 amp circuit current,
the appropriate wire size is 10 AWG.

Could anybody shed some light?

Thanks

R. Hoffman #687R
Eugene, OR USA

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For those looking for help sizing the wiring in your plane, try the wire
sizing spreadsheet provided on the Kit Planes web page. Go to
www.kitplanes.com , click on the features tab, click on the supplemental
material area, and then go the section called 'Dahlgrens Wire Sizing
Spreadsheet'. I used this in designing the wiring on my Super Rebel. I
checked the calculations the spreadsheet did against the FAA tables and all
seemed to agree. Additionally when we hooked up the 12V battery to the
plane and threw the master switch we did not notice any major fires so that
bodes well for the accuracy of the spreadsheet. Hope this helps.

Chris Gill
Super Rebel #025, Anchorage, AK

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