Accessing breaker panel

[EricJ]

32 minutes ago, Yetti said:

here is an interesting one that I did not know till installing the dynon. There is enough noise in the P Leads that you use them for an electronic tach.   With a resistor inline to settle some of the noise.  

That's why they should be shielded wire.  Checking p-lead shield grounding should be part of diagnostics for noise issues.

 

[PT20J]

1 hour ago, EricJ said:

That's why they should be shielded wire.  Checking p-lead shield grounding should be part of diagnostics for noise issues.

 

Which brings up an interesting question: how to ground the shield? John Schwaner recommends grounding at the magneto. Slick recommends grounding at the ignition switch. My plane had both ends grounded when it had the Bendix dual mag. 

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[EricJ]

Just now, PT20J said:

Which brings up an interesting question: how to ground the shield? John Schwaner recommends grounding at the magneto. Slick recommends grounding at the ignition switch. My plane had both ends grounded when it had the Bendix dual mag. 

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The wiring diagram for my airplane shows both ends being grounded for every section.    Usual practice in EE-land is that you only ground one end of a wire shield in order to prevent ground loops through the shield, and I always wondered why aviation applications usually show both ends grounded.   I suspect it is just for redundancy so that if one end of the shield becomes disconnected it still works properly.    The alternator field wire on my airplane is shown in the MM as grounded on both ends forward of the firewall, but the connection at the alternator has been long gone.   It's still good at the cannon plug on the firewall, though, so good to go...   

[Yetti]

9 hours ago, EricJ said:

The wiring diagram for my airplane shows both ends being grounded for every section.    Usual practice in EE-land is that you only ground one end of a wire shield in order to prevent ground loops through the shield, and I always wondered why aviation applications usually show both ends grounded.   I suspect it is just for redundancy so that if one end of the shield becomes disconnected it still works properly.    The alternator field wire on my airplane is shown in the MM as grounded on both ends forward of the firewall, but the connection at the alternator has been long gone.   It's still good at the cannon plug on the firewall, though, so good to go...   

Yep but they are kind of ungrounded at the cannon plug that goes through the firewall.   The shield is grounded to the screws on the cannon connector.  Since the wires are soldered into the cannon connector that seemed like a good place to solder in the tach wires.  

[EricJ]

2 hours ago, Yetti said:

Yep but they are kind of ungrounded at the cannon plug that goes through the firewall.   The shield is grounded to the screws on the cannon connector.  Since the wires are soldered into the cannon connector that seemed like a good place to solder in the tach wires.  

At a minimum that shield connection should pass through to the shield connection on the other side of the connector.    The shield shouldn't be left floating anywhere, and should ideally be grounded only on the end(s).

 

[Yetti]

2 hours ago, EricJ said:

At a minimum that shield connection should pass through to the shield connection on the other side of the connector.    The shield shouldn't be left floating anywhere, and should ideally be grounded only on the end(s).

 

Agreed.   I am pretty sure that the ground is picked up on the other side of the firewall.   I've never had the switch out so I would assume some sort of termination on that end.   And the mags are terminated in two places.