Schielding and grounding

[PBY Catalina]

Hello everybody,


A question for the electronic engineers.
To my knowledge, to avoid static, shielding should be grounded only on one extremity of each harness, and not on both ends, trying to obtain a star shape diagram, and avoiding loops in the grounding of the shields.


Now let’s have a look on the rudder position/strobe light schematic of the Carbon Cub EX2 as an example.

Capture d’écran 2022-03-05 à 14.01.59.jpg


For me this schematic is perfectly correct as the shield is grounded at the front of the harness and not at the back.


Now, why are we suggested to ground the rear shield (blue wire) near the data plate?
(https://forum.cubcrafters.com/showth...ghlight=shield)
For me it creates a loop in the shielding, and it’s a source of static in the audio system.
I’m I wrong somewhere?

[ceslaw]

Perhaps it grounds the rudder frame since the connection hinge points to the fuselage frame would not be a reliable ground connection.

Just a guess since I don't have access to the wiring on my plane at the moment.

Just goes to show, for every rule there is an exception.

Good find, and good question!

[Daveembry]

Well I’m certainly no “electronic engineer”, and didn’t stay at a Holiday Inn Express last night, but……I do just happen to have a photo here of that ground wire. Notice that the blue wire used to ground to the tab is a separate wire (not part of the 4 wire harness). The white/green wire of that 4 wire is the ground and is connected to the grounding tabs on the fuse, under the panel.

Notice they do the same on each of the wing harnesses as well? This wire attached to the shields of each wire on each side of the connector.....looks like it just joins it to keep it together?

Notice in the wing root nav light harness, it has that extra plug as well for that wire? Remember that separate ground wire we attached to the end of each spar near the nav light light on each wing. Those are a separate ground wire from the harness. Other than that, I have no idea except “it works” the way they designed it so that’s what I do.

7A961805-33DF-4850-A77E-81CAC8F8ECA7.jpg


909F0748-7369-43C8-99C6-2CE9AA4C3DF8.jpg

Hello everybody,


A question for the electronic engineers.
To my knowledge, to avoid static, shielding should be grounded only on one extremity of each harness, and not on both ends, trying to obtain a star shape diagram, and avoiding loops in the grounding of the shields.


Now let’s have a look on the rudder position/strobe light schematic of the Carbon Cub EX2 as an example.

Capture d’écran 2022-03-05 à 14.01.59.jpg


For me this schematic is perfectly correct as the shield is grounded at the front of the harness and not at the back.


Now, why are we suggested to ground the rear shield (blue wire) near the data plate?
(https://forum.cubcrafters.com/showth...ghlight=shield)
For me it creates a loop in the shielding, and it’s a source of static in the audio system.
I’m I wrong somewhere?

[Andy]

It's not too difficult to find an opinion on shield grounding that supports whichever grounding method you prefer.

Out of curiosity I looked at some of the many system interconnect examples shown in the Garmin G3X Touch Installation Manual. In almost all cases the shield is shown grounded at both ends. The only exceptions I found were for some of the audio signal cables.

How the shield is terminated may depend on the primary purpose of the shield. In some applications the shield is intended to prevent radiation from the shielded conductor(s). In other applications the shield is intended to protect the shielded conductor(s) from external signal/noise sources.

The lighting wiring is most likely shielded to prevent it radiating.

I have spent some time looking at various CubCrafters wiring schematics and have formed the opinion that they do not always reflect the current build standard. I would guess that CubCrafters found the tail strobe caused less interference when the shield was grounded but did not publish a revised wiring schematic.

[PBY Catalina]

Thank you all.
I can’t say enough about how helpful your answers and Pete’s are to me.


In this specific case of the blue wire connected to the plate, I think I found an explanation by looking more closely at the wires that come out of the rudder.


There is a white/black wire without connector.
For me, this is the end of the shielding of this harness.


I will connect the blue wire to this white/black one and so I will be perfectly in agreement with the CC diagram and it seems to me that this is also the logic way to do that shielding. Connecting that blue to the data plate is for me not correct.


I have another question to ask you about the wiring of the headers. I will give you a new message about this.


Have a nice WE !
Yves

IMG_7848 - copie.jpg

IMG_7849.jpg

[Andy]

I will connect the blue wire to this white/black one and so I will be perfectly in agreement with the CC diagram and it seems to me that this is also the logic way to do that shielding. Connecting that blue to the data plate is for me not correct.

I would expect the shield to be continuous from the airframe harness to the rudder harness. Since the connector is only 4 pin the shield needs to be linked separately.

What you have to decide is whether to also bond the shield to airframe using a separate pigtail.

The photo in the thread you linked earlier - https://forum.cubcrafters.com/showth...ghlight=shield shows that harness was fabricated with provision for linking the shield and bonding the shields (2 separate pigtails connected to the shield).

Why is your harness not the same as shown in that photo?

Do your wing lighting harnesses have provision for bonding the shield or only for linking the shield?

[Daveembry]

No. You are to attach a connector to that white/black wire and it attaches to that connector on that blue wire in the photo I shared. The other end of that blue wire goes to the data plate as a ground.

you can’t connect the blue wire to just it….the blue wire has 2 ends. One attaches to the data plate and the other has the red connector that attaches to the connector you add into the black/white wire.

this is the way all 3 nav lighting harnesses are done and grounded.

Trust me, that’s the way it goes. Here’s a bad sketch I did to show it. The end of the wire at the end of the wing is attached to the spar web itself…….just like the end of the rudder light harness is attached to the data plate as a ground.

D362D1FB-A0B2-4FD3-AA66-21CD5B026DBF.jpg

Thank you all.
I can’t say enough about how helpful your answers and Pete’s are to me.


In this specific case of the blue wire connected to the plate, I think I found an explanation by looking more closely at the wires that come out of the rudder.


There is a white/black wire without connector.
For me, this is the end of the shielding of this harness.


I will connect the blue wire to this white/black one and so I will be perfectly in agreement with the CC diagram and it seems to me that this is also the logic way to do that shielding. Connecting that blue to the data plate is for me not correct.


I have another question to ask you about the wiring of the headers. I will give you a new message about this.


Have a nice WE !
Yves

IMG_7848 - copie.jpg

IMG_7849.jpg

[Daveembry]

note also that with this wiring, the “shield” IS only grounded at 1 end. The wiring harness ground wire is not the shield. The CC wiring harness and schematics are correct.

No. You are to attach a connector to that white/black wire and it attaches to that connector on that blue wire in the photo I shared. The other end of that blue wire goes to the data plate as a ground.

you can’t connect the blue wire to just it….the blue wire has 2 ends. One attaches to the data plate and the other has the red connector that attaches to the connector you add into the black/white wire.

this is the way all 3 nav lighting harnesses are done and grounded.

Trust me, that’s the way it goes. Here’s a bad sketch I did to show it. The end of the wire at the end of the wing is attached to the spar web itself…….just like the end of the rudder light harness is attached to the data plate as a ground.

D362D1FB-A0B2-4FD3-AA66-21CD5B026DBF.jpg

[PBY Catalina]

Yes, you are right, Dave and Andy...

Apparently there is a provision for the shield to be BOTH grounded AND linked to the rudder harness from this position.
Still that I don't understand why it should be grounded at this position and that it's not indicated like that on the CC diagram. There is maybe a reason, for this double shield grounding and Pete will give it later during the week. But as long as you both confirm that it does not create any static (something I'm really concerned about, in experimentals) I thrust you and I will connect that blue on to the plate.

Thanks guys !

[PBY Catalina]

note also that with this wiring, the “shield” IS only grounded at 1 end. The wiring harness ground wire is not the shield. The CC wiring harness and schematics are correct.

For me yes, the shield of this harness is grounded at 2 ends like that....