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nuckolls.bob(at)aeroelect
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Posted: Mon May 06, 2013 10:58 am Post subject: Question

At 01:24 PM 5/6/2013, you wrote:

  	  Quote: 	
		  Hello Bob,

  

 I have a quick question- 

  

 Why is it that a radio like a Garmin SL-30 Nav/Com and a marker beacon like a PS Engineering model, have two separate ground wires each, i.e. one for the power ground and one for the audio ground – yet those wires end up connecting at the same grounding point.

  

 I am curious as to why there has to be two wires from each box that end up at the same grounding point, instead of the manufacturer wiring these two grounds up together internally in the device, and then only using one ground wire?

  

 Many thanks, 	


    Not sure what you're referring to. Here's one of serveral

    wiring diagrams gleaned from an SL-30 installation manual:



 [img]cid:7.1.0.9.0.20130506135347.04cf1500(at)aeroelectric.com.0[/img] 



    In this case, I suspect that pins 13, 7 and 9 are

    all common inside the SL-30 but only pin 9 is used

    for attachment to ship's power ground. Pins 13 and

    7 become a quasi-single point ground for the audio

    system as it relates to the SL-30. Are there other

    wiring diagrams that offer a more confusing picture?



 

   Bob . . .

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nuckolls.bob(at)aeroelect
Guest

Posted: Wed May 08, 2013 8:57 am Post subject: Question

 	  Quote: 	
		   

 So there it is, that 9 and 13 are grounds, running to the same AMP connector. This is what I was asking.  Why are there 2 independent wires which end up going to the same AMP connector with 30 some pins on it that are all grounded together? 

  

 Then in the bottom diagram for a PS Engineering marker beacon, pin 9 is the power ground and pin 14 is the audio ground.   So am I correct in assuming that they also end up at the same 30 some pin AMP connector – since the SL-30 pins for power ground and audio ground both end up there? 	


   I cannot know the reasoning behind any particular

   design decision unless it is specifically explained

   in the manufacturer's documents. I can attest to the

   my notion (shared by some) that many products miss

   an opportunity to make a device easier to install

   by making otherwise unneeded pins extra grounds.



   This gives the installer an opportunity to neatly

   terminate pigtails for shields on their own pin

   in the connector. I have generated two widely

   used, multiple connection grounding products. One

   is the firewall ground bus sold by B&C, the other

   is the panel/avionics ground bus offered on my

   website.  There are no specific assignments for

   where connections are made on these products. My

   architecture drawings feature ground symbols labeled

   so as to suggest termination at a specific ground

   bus . . . but not on any particular pin.



   I am always pleased to see manufacturer's wiring

   diagrams that offer dedicated ground pins for all wires

   needing ground . . . but sometimes, it's simply

   not possible to have plenty of grounds for all

   contingencies.



   There is nothing 'magic' about a proliferation

   of grounds in any given connector. 

   



 

   Bob . . .    [quote][b]

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