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Magnetos connection to ground

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trigo(at)mail.telepac.pt
Guest

Posted: Sat Dec 03, 2016 5:08 am Post subject: Magnetos connection to ground

Guys



Which is the best practice to connect the Magnetos Ground terminals to the Firewall Ground "forest"?

Is it recommended to wire Left and Right magnetos with separate wires, or can they be connected to each other and then to the Ground forest?



And how about the wires to be used, should they be shielded or unshielded? Which gauge?



One more question: for the connections from the ignition switch to both magnetos, I am using shielded wires, so should the shields be connected on both sides (like it is recommended in Tony Bingelis' books), or only on one side? 

In this last case, the shield should be connected in the magneto side, so is it good to connect the shield to the Ground terminal of the magneto?



Thanks in advance

Carlos

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ceengland7(at)gmail.com
Guest

Posted: Sat Dec 03, 2016 5:45 am Post subject: Magnetos connection to ground

On Sat, Dec 3, 2016 at 7:04 AM, Carlos Trigo <trigo(at)mail.telepac.pt (trigo(at)mail.telepac.pt)> wrote:

 	  Quote: 	
		  --> AeroElectric-List message posted by: Carlos Trigo <trigo(at)mail.telepac.pt (trigo(at)mail.telepac.pt)>

 

 Guys

 

 Which is the best practice to connect the Magnetos Ground terminals to the Firewall Ground "forest"?

 Is it recommended to wire Left and Right magnetos with separate wires, or can they be connected to each other and then to the Ground forest?

 

 And how about the wires to be used, should they be shielded or unshielded? Which gauge?

 

 One more question: for the connections from the ignition switch to both magnetos, I am using shielded wires, so should the shields be connected on both sides (like it is recommended in Tony Bingelis' books), or only on one side?

 In this last case, the shield should be connected in the magneto side, so is it good to connect the shield to the Ground terminal of the magneto?

 

 Thanks in advance

 Carlos 	
Hi Carlos,

You don't need to carry the mag ground to the firewall. The wire from the mag to the switch should be a shielded wire, with the center conductor tied to the 'P' lead terminal and the shield tied to the mag's case, using any convenient screw on the case. The mag's case is electrically bonded to the engine, and the engine has a ground to the firewall/battery negative. The other end of the wire should have the center (P-lead) tied to one of the terminals on your switch, and the shield tied to the other terminal (or the ground terminal, if you're using a key type switch). No need to ground it locally near the switch, and I don't do it, since there's the potential of injecting mag noise into your other electronics. Grounding it locally gives the noise you're trying to shield an additional path to follow, which may be around/through other electronics. Grounding it locally can also mask a failed shield connection, because the P lead would still be shorted to ground even with the shield broken. The hazard of this is when you (or worse, someone else) is doing maintenance. If you have a broken shield & don't know it, everything will appear to be normal until someone is doing maintenance & removes a ground wire for electrical safety. If this ungrounds the engine from the rest of the airframe, the mag is now 'hot', even with the mag switch 'off'.

The shielded P-lead has a dual purpose. While the engine is operating, the shield is grounded only at the mag and functions purely as a shield, to limit the radiated noise from the mag. When you turn off the mag, you're actually closing the switch contacts, and the shield serves as the ground return to short out mag's primary coil. 

Charlie

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ceengland7(at)gmail.com
Guest

Posted: Sat Dec 03, 2016 10:04 am Post subject: Magnetos connection to ground

On Sat, Dec 3, 2016 at 7:44 AM, Charlie England <ceengland7(at)gmail.com (ceengland7(at)gmail.com)> wrote:

 	  Quote: 	
		  



On Sat, Dec 3, 2016 at 7:04 AM, Carlos Trigo <trigo(at)mail.telepac.pt (trigo(at)mail.telepac.pt)> wrote:

 	  Quote: 	
		  --> AeroElectric-List message posted by: Carlos Trigo <trigo(at)mail.telepac.pt (trigo(at)mail.telepac.pt)>

 

 Guys

 

 Which is the best practice to connect the Magnetos Ground terminals to the Firewall Ground "forest"?

 Is it recommended to wire Left and Right magnetos with separate wires, or can they be connected to each other and then to the Ground forest?

 

 And how about the wires to be used, should they be shielded or unshielded? Which gauge?

 

 One more question: for the connections from the ignition switch to both magnetos, I am using shielded wires, so should the shields be connected on both sides (like it is recommended in Tony Bingelis' books), or only on one side?

 In this last case, the shield should be connected in the magneto side, so is it good to connect the shield to the Ground terminal of the magneto?

 

 Thanks in advance

 Carlos 	
Hi Carlos,

You don't need to carry the mag ground to the firewall. The wire from the mag to the switch should be a shielded wire, with the center conductor tied to the 'P' lead terminal and the shield tied to the mag's case, using any convenient screw on the case. The mag's case is electrically bonded to the engine, and the engine has a ground to the firewall/battery negative. The other end of the wire should have the center (P-lead) tied to one of the terminals on your switch, and the shield tied to the other terminal (or the ground terminal, if you're using a key type switch). No need to ground it locally near the switch, and I don't do it, since there's the potential of injecting mag noise into your other electronics. Grounding it locally gives the noise you're trying to shield an additional path to follow, which may be around/through other electronics. Grounding it locally can also mask a failed shield connection, because the P lead would still be shorted to ground even with the shield broken. The hazard of this is when you (or worse, someone else) is doing maintenance. If you have a broken shield & don't know it, everything will appear to be normal until someone is doing maintenance & removes a ground wire for electrical safety. If this ungrounds the engine from the rest of the airframe, the mag is now 'hot', even with the mag switch 'off'.

The shielded P-lead has a dual purpose. While the engine is operating, the shield is grounded only at the mag and functions purely as a shield, to limit the radiated noise from the mag. When you turn off the mag, you're actually closing the switch contacts, and the shield serves as the ground return to short out mag's primary coil. 

Charlie





 	


Forgot to add, each mag should be a separate entity, with its own shielded P-lead. The only thing that should be common is (potentially) the grounding (shutdown) terminal(s) in the switch, if you're using a key-switch type control for the mags. If you're using toggles, then nothing would be common between the mags' wiring.

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nuckolls.bob(at)aeroelect
Guest

Posted: Sat Dec 03, 2016 10:33 am Post subject: Magnetos connection to ground

At 07:04 AM 12/3/2016, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: Carlos Trigo <trigo(at)mail.telepac.pt>



 Guys



 Which is the best practice to connect the Magnetos Ground terminals to the Firewall Ground "forest"?

 Is it recommended to wire Left and Right magnetos with separate wires, or can they be connected to each other and then to the Ground forest?



 And how about the wires to be used, should they be shielded or unshielded? Which gauge? 	


   They can be any size . . . but 20AWG or larger is

   sort of standard practice for mechanical robustness.

   Some OEM TC airplane guys don't use anything smaller

   than 20AWG under the cowl.



 

  	  Quote: 	
		  One more question: for the connections from the ignition switch to both magnetos, I am using shielded wires, so should the shields be connected on both sides (like it is recommended in Tony Bingelis' books), or only on one side? 

 In this last case, the shield should be connected in the magneto side, so is it good to connect the shield to the Ground terminal of the magneto? 	


   Here is the recommended configuration for managing

   p-leads.



 [img]cid:7.1.0.9.0.20161203122338.05acb038(at)aeroelectric.com.0[/img] 



   This connection philosophy offers greatest noise

   control and eliminates any potential for burning

   the p-leads with starter current in the event that

   the crankcase bonding jumper is disconnected (don't

   laugh . . . I've seen it happen twice).



 

   Bob . . .

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skywagon

Joined: 11 Feb 2006
Posts: 184

Posted: Sat Dec 03, 2016 11:25 am Post subject: Magnetos connection to ground

A comment about the P-lead mounting.

  

 That wire connection at the mag is subject to a lot of  vibration and turbulence.

 Secure the P-lead as if a room full of kindergarten kids  are going to use it as a tug of rope game.

 We all know the danger of a disconnected P-lead leaving  the mag hot and ready to fire a plug if the prop is moved.

  

   

 [quote]   ---

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stuart(at)stuarthutchison
Guest

Posted: Sat Dec 03, 2016 2:53 pm Post subject: Magnetos connection to ground

Yes, dangers such as this recent example …. that caught the pilot by surprise because the switches were left on ….  skywagon(at)charter.net (skywagon(at)charter.net)> wrote:

A comment about the P-lead mounting.

 

That wire connection at the mag is subject to a lot of vibration and turbulence.

Secure the P-lead as if a room full of kindergarten kids are going to use it as a tug of rope game.

We all know the danger of a disconnected P-lead leaving the mag hot and ready to fire a plug if the prop is moved.

 



[quote]---

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