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jabiru coil grounds

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icubob(at)newnorth.net
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Posted: Mon Jan 22, 2007 2:26 pm Post subject: jabiru coil grounds

hi bob,

  i asked this question a week ago but got no  response so i will try again. this refers to the z-20 wiring diagram for a jab  engine and ''note #3''

   i understand a shielded wire connects the  coil to the ignition switch and when the switch is turned ''off'' the coil is  grounded . i am using a keyed switch like is used in a piper. 

   i see that the shielding is grounded at the  engine.

   here comes the question.......... it seems  that the opposite end of the shielding is attached to the  ''ground''  terminal of my switch. so the switch receives it's ground thru the shielding .  am i correct?  the switch does not need a wire from the ''forest of tabs''  ground because it is using the shielding for ground. correct?

    

    if i am correct in these observations  my last question is ''why is this done like this? why not use another wire to  ground the switch and leave the ''switch end'' of the shielding unattached?  

   i appreciate your  patience.  this elect. stuff is hard enough for me when i DO  understand the reasons.

                 bob  noffs                                                                                                   

  

    [quote][b]

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nuckollsr(at)cox.net
Guest

Posted: Mon Jan 22, 2007 4:19 pm Post subject: jabiru coil grounds

At 04:23 PM 1/22/2007 -0600, you wrote:



 	  Quote: 	
		  hi bob,

  i asked this question a week ago but got no response so i will try 

 again. this refers to the z-20 wiring diagram for a jab engine and ''note #3''

   i understand a shielded wire connects the coil to the ignition switch 

 and when the switch is turned ''off'' the coil is grounded . i am using a 

 keyed switch like is used in a piper.

   i see that the shielding is grounded at the engine.

   here comes the question.......... it seems that the opposite end of the 

 shielding is attached to the  ''ground'' terminal of my switch. so the 

 switch receives it's ground thru the shielding . am i correct?  the 

 switch does not need a wire from the ''forest of tabs'' ground because it 

 is using the shielding for ground. correct?


	


   Yes



 	  Quote: 	
		  

    if i am correct in these observations my last question is ''why is 

 this done like this? why not use another wire to ground the switch and 

 leave the ''switch end'' of the shielding unattached?

   i appreciate your patience.  this elect. stuff is hard enough for me 

 when i DO understand the reasons.


	


   You don't want MULTIPLE ground conductors bringing the crankcase

   to the airframe. Grounding the shielding of p-leads at both ends

   does just that.



   Multiple ground paths are the root cause of ground-loop induced noises

   and in this case offers the potential for damaging a p-lead conductor

   and other wires bundled with it should (1) the bond strap between crankcase

   and firewall stud become disconnected and (2) an attempt is made to

   start the engine. Had a mechanic do it twice on me  . . . didn't offer

   him a third opportunity.



   Bob . . .

      ---------------------------------------------------------

      < What is so wonderful about scientific truth...is that >

      < the authority which determines whether there can be   >

      < debate or not does not reside in some fraternity of   >

      < scientists; nor is it divine. The authority rests     >

      < with experiment.                                      >

      <                            --Lawrence M. Krauss       >

      ---------------------------------------------------------

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