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  #1  
Old 06-22-2007, 04:50 PM
N787R N787R is offline
 
Join Date: Apr 2007
Location: San Jose, Ca
Posts: 56
Default Ground wire question

Where is ok to use airframe for grounding?
Landing lite, nav lite, strobes : can these be grounded to airframe?

I plan to put strobe power supply in the wing tips.

Thanks

N787R
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  #2  
Old 06-22-2007, 06:34 PM
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Ironflight Ironflight is offline
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Default

787R,

You'll obviously get a number of opinions on grounding...

I grounded most items such as lights and pitot heat locally. Things with shielded wires, I followed the shielding requirements. Avionics and such are all common-point grounded in the panel. I have had no problems at all in over 500 hours of flying, no noise or feedback (that wasn't quickly fund to be unintended ground loops in the audio circuits). I have been flying factory airplanes using all local grounds for over three decades, so I figured it's simple and works....

Of course, there are two sides (at least) to every issue!

Paul
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  #3  
Old 06-22-2007, 06:48 PM
Bob Axsom Bob Axsom is offline
 
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Default Anywhere

There are one or two cases where I ran a return wire all the way back to the box but I can't remember which one or why anymore. My instrument panel bottom edge is saturated with ground point holes an inch or less apart. When I was a radio, electrical and electronic inspector at McDonnell after getting out of the Air Force where I was a radio mechanic we inspected all grounds for several requirements but basically they were: the surface had to be prepared by removing any organic coatings with a rotary bonding brush, and AN960D washer had to be installed next to the aircraft structure to position the dissimilar metal contact between the terminal and the washer instead of the structure, a locking provision such as a split lock washer or a platenut had to be included in the hardware stack, the terminals had to be arranged in a fanned out configuration to allow good terminal contact without barrell stack stress and no more that four wires could be terminated at one point. On our RV-6A I made a concious effort to bring all of the grounds to the main "single point" ground on the firewall with a copper path but it is not done in all cases (a wire runs from the instrument panel to the firewall common ground for example) and I'm confident it is no necessary. Some concern for EMI needs to be exercised in special cases like the strobes but it sounds like you have addressed that. After 3+ years of operation there have been no grounding problems with our airplane.

Bob Axsom
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  #4  
Old 06-22-2007, 08:32 PM
Rick S. Rick S. is offline
 
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Location: Las Vegas
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Bob,

Wow....I forgot all that aircraft ground bonding procedures. Brings back memorys. I recall going on the hunt many nights for all the right chemicals the Tech Data called for while scratching my head as to why we needed to use them in the first place. Then I had this corrosion class and it explained all the reasons.
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  #5  
Old 06-22-2007, 10:14 PM
Jekyll Jekyll is offline
 
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Bob Nuckolls published an update last year to his book showing suggested grounds: local, panel and firewall. It is Z15.3.1. I looked for it on his site but didn't find it. Try going to the Aeroelectric forum at Matronics and doing a search:

http://forums.matronics.com/

To answer your questions: yes, yes, yes and yes.

Practice good bonding techniques per Bob Axsom's post. Check FAA Circular AC43.13B for details and examples of proper grounding techniques.

Jekyll
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  #6  
Old 03-15-2010, 08:14 AM
foka4 foka4 is offline
 
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Location: Ankeny, IA
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Default Source for AN960D washers?

Where do you get AN960D aluminum washers for airframe electrical connections? I don't see them listed at any of the usual suppliers.

Thanks,

Matthew
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  #7  
Old 03-15-2010, 09:16 AM
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FlyingArcher FlyingArcher is offline
 
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Location: Andernos les Bains, France
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Default GAHCo

Quote:
Originally Posted by foka4 View Post
Where do you get AN960D aluminum washers for airframe electrical connections? I don't see them listed at any of the usual suppliers.

Thanks,

Matthew
GAHCo has them here
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  #8  
Old 03-15-2010, 09:56 AM
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az_gila az_gila is offline
 
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Post There is a caution though...

A lot of the aluminum washers I have seen have been grey anodized. This surface treatment is non-conductive and, for obvious reasons, should not be used...

Since the washer is plain old 2024-T3 and is just a sacrificial element in the stack, you could even make your own -- heck - it usually doesn't even need to be round...

GAHCo info here, including equivalent NAS numbers -

http://www.gen-aircraft-hardware.com...minum-2024.pdf
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  #9  
Old 03-16-2010, 05:26 AM
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f1rocket f1rocket is offline
 
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From my experience, there are three ground connections that you want to be careful with, the rest you can ground locally. The three are the radio grounds, headset grounds, and strobes. Follow the instructions carefully on these three and you should be okay.
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  #10  
Old 03-25-2010, 10:05 PM
elippse elippse is offline
 
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Location: Arroyo Grande, CA
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Default Grounding

Flying a composite plane, I have to supply a pair of wires to each load, source and return; I avoid the use of the term "ground" since you usually leave that behind when you take off. In my case I usually use shielded twisted pair to give good EMI and RFI protection. But be aware that if you carry current across a riveted joint, sooner or later you're going to get galvanic corrosion if even a tiny bit of moisture gets into the gap.
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