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Shield grounds for CDI

W

WHB

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Apologies in advance if this is not the correct section.

Looking to interface a GNS-430W with a MD200-306 CDI. Based on the Garmin installation manual, shield grounds should be terminated at both the GNS and the CDI (first picture below). I understand that shield grounds are terminated on the GNS end via the connector backshell. However, there is no provision for terminating the shield grounds on the CDI connector backshell (second picture).

Do the cable shields need to be grounded at the CDI end? If so, how?

The Garmin manual (in note 2) seems to indicate connecting shield grounds to "aircraft chassis." Do people actually do this? Harnesses I've seen don't have any provision for shield grounding at the CDI.
 

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There'll be a power/lighting ground wire on the connector to the CDI, the shield drains could all be daisy chained to that.

When terminating to the "chassis" (local ground), installers will run an extra wire in the connector harness back a suitable distance so that you still have an adequate service loop. Then that ground wire will terminated somewhere on the airframe.

When I do deletions of old wiring before installing new stuff, I find ground studs in all kinds of places and all kinds of different ways.
 
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MD222-406 PIN OUT

My apologies to WHB if I hijack this thread a little :eek: but I have a quick question for the avionics gurus here..

---------------
By looking at the Pin Out diagram posted here, I'm wondering if anyone will know if the Pin Out for a MD222-406 to a GNS-480 is the same than the one for a GNS-430..

Mine ( CDI )is acting funny and I would like to know if it is wired properly..

I appreciate the help

Thanks

Bruno
 
GND

You need a D-sub connector made of metal for a certified installation.
Garmin uses metal connectors.
Aircraft spruce has metalised plastic D-sub connectors.

Good luck
 
N804RV said:
There'll be a power/lighting ground wire on the connector to the CDI, the shield drains could all be daisy chained to that.

When terminating to the "chassis" (local ground), installers will run an extra wire in the connector harness back a suitable distance so that you still have an adequate service loop. Then that ground wire will terminated somewhere on the airframe.

When I do deletions of old wiring before installing new stuff, I find ground studs in all kinds of places and all kinds of different ways.
Click to expand...

Thanks, Ken! That makes a lot of sense.
 
Avanza said:
You need a D-sub connector made of metal for a certified installation.
Click to expand...

The MD200 IM calls out p/n 7014517 as the connector, which is the plastic posi-loc pictured above.

The MD200 IM does not reference shield grounds anywhere, other than saying to use shielded cable.
 
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WHB said:
The MD200 IM calls out p/n 7014517 as the connector, which is the plastic posi-loc pictured above.

The MD200 IM does not reference shield grounds anywhere, other than saying to use shielded cable.
Click to expand...

That backshell on the connector in the picture looks like it has a metal strain relief. If there's continuity between the strain relief and the CDI casing when its connected, you could just daisy chain the shield drains to one of the screws on the strain relief, using a small PIDG ring terminal, and it would work just like the Garmin scheme.

I hate those old slide-lock style backshells that MidContinent is so fond of using on their dsub connectors.
 
N804RV said:
If there's continuity between the strain relief and the CDI casing when its connected, you could just daisy chain the shield drains to one of the screws on the strain relief, using a small PIDG ring terminal, and it would work just like the Garmin scheme.
Click to expand...

Unfortunately there isn't continuity, the metal strain relief is only attached to the plastic body/backshell.
 
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