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Light pigtail

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rvg8tor

Joined: 06 Apr 2009
Posts: 50
Location: Olympia, WA

Posted: Sun Sep 02, 2012 11:52 pm Post subject: Light pigtail

I think it is called a pigtail  I originally wired my RV-8A to use Van's 75W halogen landing and taxi light system.  I ran 16 AWG wire from a 15A breaker to the switch, the switch is set up as OFF-TAXI-LAND, so power only goes to either the landing light set (2 bulbs on each wing) or landing light set.



I have decided to now go with a fancy LED landing taxi light.  This light comes with a pigtail out of a circuit unit and the wire is 18AWG except the ground is 16AWG, only 1 ground for entire light sytem.  I have wired this into the plane and it works fine but then I am thinking I need to go down to a 10A breaker.  These lights pull under 3 amps each so not a lot of draw.  Would I do okay to leave things as they are, one 16 AWG wire to the switch that in turn feeds either wires to the taxi light or wires to the landing light, all 16AWG.  My only issue is with the wires going into the light housing, the power wires are 18AWG and the ground is 16 AWG.  Perhaps an inline fuse at the transition would be in order to protect the short run of 18AWG wire?  Now that I think about it the pigtail is only about 4" so maybe I am okay, and they only have one 16AWG wire as the return.



The manufacturer recommended set up is two 10A breakers to two switches and one 16AWG ground as the return path.



Sorry for the long post, this is late at night and I am half brainstorming my issue with this post.  I appreciate any light one can shed, pun intended.



Cheers

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_________________
Mike "Nemo" Elliott
RV-8A QB (Engine)
www.mykitlog.com/rvg8tor

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Sep 03, 2012 6:28 am Post subject: Light pigtail

The manufacturer recommended set up is two 10A breakers to two 

switches and one 16AWG ground as the return path.



         It would help to see the manufacturer's installation

         instructions along with any wiring diagrams offered.

         If these are LED fixtures, then 10A is WAAAaaayyy too

         big.



Sorry for the long post, this is late at night and I am half 

brainstorming my issue with this post.  I appreciate any light one 

can shed, pun intended.



         Need DATA on the proposed lighting fixtures.

   Bob . . .

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rvg8tor

Joined: 06 Apr 2009
Posts: 50
Location: Olympia, WA

Posted: Mon Sep 03, 2012 7:36 am Post subject: Re: Light pigtail

Attached are the instructions, I used for the install.  They include a wire diagram.  I am currently not going to hook up the Wig Wag feature, this was not planned when I wired the plane a couple years ago, I will add this feature after I am flying this year with any luck!



Cheers



Can't seem to get the file to attach, the instructions can be found here;



http://aircraftspruce.com/catalog/pdf/11-09675.pdf

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_________________
Mike "Nemo" Elliott
RV-8A QB (Engine)
www.mykitlog.com/rvg8tor

nuckolls.bob(at)aeroelect
Guest

Posted: Mon Sep 03, 2012 10:45 am Post subject: Light pigtail

At 10:36 AM 9/3/2012, you wrote:




Attached are the instructions, I used for the install.  They include 

a wire diagram.



    Hmmmm . . . the wiring is, shall we say, unconventional.

    Circuit protection is usually installed at the bus

    UPSTREAM of control switches. Assuming the stated

    current draw numbers are for EACH of TWO fixtures, then

    system demands for Landing lights is 4.4A and Taxi lights

    is 5.8A. Position lights would be something less than 1A

    average.



    The nominal wire sizing is a bit heavy, the whole system

    could be wired with 20AWG and breakered at 7A, or

    fused at 10A (Don't want to operate past the 1/4th derating

    for fuses in the Taxi light slot. Position lights could

    run from a 5A branch. While the control wires are probably

    properly sized for loads, it's a good practice not to wire

    airframe accessories with less that 22AWG just for general

    robustness and workability issues.



   I am currently not going to hook up the Wig Wag feature, this was 

not planned when I wired the plane a couple years ago, I will add 

this feature after I am flying this year with any luck!



    If your wires are in place, then the notion of

    downsizing breakers or fuses consistent with new

    system requirements is a reasonable thing to do.

   Bob . . .

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mrspudandcompany(at)veriz
Guest

Posted: Mon Sep 03, 2012 11:31 am Post subject: Light pigtail

Attached are the instructions, I used for the install.  They include 

a wire diagram.



    Hmmmm . . . the wiring is, shall we say, unconventional.

    Circuit protection is usually installed at the bus

    UPSTREAM of control switches. Assuming the stated

    current draw numbers are for EACH of TWO fixtures, then

    system demands for Landing lights is 4.4A and Taxi lights

    is 5.8A. Position lights would be something less than 1A

    average.



    The nominal wire sizing is a bit heavy, the whole system

    could be wired with 20AWG and breakered at 7A, or

    fused at 10A (Don't want to operate past the 1/4th derating

    for fuses in the Taxi light slot. Position lights could

    run from a 5A branch. While the control wires are probably

    properly sized for loads, it's a good practice not to wire

    airframe accessories with less that 22AWG just for general

    robustness and workability issues.



   I am currently not going to hook up the Wig Wag feature, this was 

not planned when I wired the plane a couple years ago, I will add 

this feature after I am flying this year with any luck!



    If your wires are in place, then the notion of

    downsizing breakers or fuses consistent with new

    system requirements is a reasonable thing to do.

   Bob . . . 

		Question:  If I understand correctly the plan is to use the

existing wiring, which was sized originally to the existing

breakers.  I understand that the breakers are oversize for the 		new

lights, but why would it be suggested to lower the current

rating size of the breaker, since it is there only to protect 		the

wire?

		Roger

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rvg8tor

Joined: 06 Apr 2009
Posts: 50
Location: Olympia, WA

Posted: Tue Sep 04, 2012 6:49 am Post subject: Re: Light pigtail

 	  mrspudandcompany(at)veriz wrote: 	
		  Attached are the instructions, I used for the install.  They include 

a wire diagram.



    Hmmmm . . . the wiring is, shall we say, unconventional.

    Circuit protection is usually installed at the bus

    UPSTREAM of control switches. Assuming the stated

    current draw numbers are for EACH of TWO fixtures, then

    system demands for Landing lights is 4.4A and Taxi lights

    is 5.8A. Position lights would be something less than 1A

    average.



    The nominal wire sizing is a bit heavy, the whole system

    could be wired with 20AWG and breakered at 7A, or

    fused at 10A (Don't want to operate past the 1/4th derating

    for fuses in the Taxi light slot. Position lights could

    run from a 5A branch. While the control wires are probably

    properly sized for loads, it's a good practice not to wire

    airframe accessories with less that 22AWG just for general

    robustness and workability issues.



   I am currently not going to hook up the Wig Wag feature, this was 

not planned when I wired the plane a couple years ago, I will add 

this feature after I am flying this year with any luck!



    If your wires are in place, then the notion of

    downsizing breakers or fuses consistent with new

    system requirements is a reasonable thing to do.

   Bob . . . 

		Question:  If I understand correctly the plan is to use the

existing wiring, which was sized originally to the existing

breakers.  I understand that the breakers are oversize for the 		new

lights, but why would it be suggested to lower the current

rating size of the breaker, since it is there only to protect 		the

wire?

		Roger 	




This is ultimately my question as well, to change the breaker is a bit of a pain at this point and since it does protect the wire I was hoping to leave the installation as is.  I know the wire is way bigger than needed.  My risk is the pigtail out of the light, the power wires are 18 AWG but they are very short.  In a dead short, do you think the breaker would still pop before the 18AWG wires burned up?

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_________________
Mike "Nemo" Elliott
RV-8A QB (Engine)
www.mykitlog.com/rvg8tor

nuckolls.bob(at)aeroelect
Guest

Posted: Tue Sep 04, 2012 7:25 am Post subject: Light pigtail

> Question:  If I understand correctly the plan is to use the

 > existing wiring, which was sized originally to the existing

 > breakers.  I understand that the breakers are oversize for the

 > new lights, but why would it be suggested to lower the current

 > rating size of the breaker, since it is there only to protect

 > the wire?

 >

 >

 >               Roger

This is ultimately my question as well, to change the breaker is a 

bit of a pain at this point and since it does protect the wire I was 

hoping to leave the installation as is.  I know the wire is way 

bigger than needed.  My risk is the pigtail out of the light, the 

power wires are 18 AWG but they are very short.  In a dead short, do 

you think the breaker would still pop before the 18AWG wires burned up?



   Absolutely. Breakers actually don't even protect the

   wire but the wire's insulation. See:



http://tinyurl.com/6qr72fr



   Leaving the breakers in place represents no risk

   to comfortable termination of flight under the

   worst case failures. Even if those wires DID burn up,

   what's the additional risk to an assembly that's already

   in trouble?



   Wire sizing and associated protection calls for

   considering a huge combination of factors for

   load dynamics, environment, and effects of any

   given failure.



   The philosophy for wire and protection sizing is

   VERY conservative consistent with not wasting a

   lot of time doing an FMEA for EACH protected

   branch. AC43-13 is technically correct but

   philosophically pedantic . . . but consider

   the authorship . . .

   Bob . . .

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