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Tying together a bunch of grounds

N546RV

Well Known Member
Time for today's potentially-stupid question. As I keep building my harness, I've got a few spots where I'm tying wires together with window splices, but I'm looking ahead to the intercom wiring and trying to imagine what this will look like.

To be very clear, this isn't a question of what gets connected where, but rather of what those connections will physically look like.

Looking at my schematic, I'm going to have eight ground nodes tied together at the intercom connection: six shields (mic and phones for two seats plus audio/mic to the com radio), plus two sleeve grounds for the headset phone jacks. All those will need to be tied to a ground wire running from a pin on the Dynon intercom to the ground bus on the firewall.

Are people handling this by just doing some sort of inline splices? One big splice attaching eight wires to a window in another wire seems both challenging and ill-advised. Maybe I need to go looking for a different D-sub backshell with grounding screws; the Dynon intercom just came with a basic plastic one.

Photos or descriptions of how everyone handled this would be greatly appreciated.
 
You want to use shield terminations and daisy chain the grounds and then run the last one to ground. Hopefully pic helps.
 

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Intercom Shields

Here is how I terminated 13 shields on my intercom.
 

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You want to use shield terminations and daisy chain the grounds and then run the last one to ground. Hopefully pic helps.

Ohhh...you know, I think I read the daisy-chain approach when I was looking for other posts like this, but somehow it didn't occur to me exactly how it could work. I was thinking it'd be the same old "one big splice" problem.

But now it occurs to me that for each of my solder sleeves, I can insert more than one ground termination wire, and make this stupidly simple. All the shields get chained together that way, I can also insert the two ring-terminal wires into one as well, and finally have a short pigtail that gets window spliced to the long wire from the intercom ground pin to the ground bus.

Funny how obvious things don't always become obvious until pointed out. Thank you!
 
Certainly you can daisy chain the grounds, but I'm not sure I would do it that way. Think about if you need to make a change later and you have to cut the chain.

Depending on the type of audio panel you have there are a couple of options. Some have a single stud to attach the grounds. I initially had one like that. I did combine some of the grounds using ring lugs prior to attaching to the grounds. If you have a Garmin audio panel then they have nice shielded connectors which have shield attachment points. Again you can combine some wires into ring lugs to minimize the number of attachments.

Also I suggest you leave the wires slightly longer so if you need to cut off a ring lug then the remaining wire is still long enough to reinstall in another crimp terminal.
 
One of those nice shielded connectors would be great for this - and I do like that better than permanently attaching the daisy chain. I'm not sure how easy they are to get though; I took a brief look at Digikey earlier and it wasn't immediately obvious if they had them. That says more about the amount of time one can spend searching for components there than about whether or not they actually carry them, though.
 
FOT

I'm following. Not crazy about daisy chain solder sleeves. As mentioned, cutting one out creates a bunch of work. How about a Forest of Tabs?
 
Been thinking this one over some more today. I haven't had any luck finding a D-sub hood with a nice ground block like the Garmin connectors. Another discussion I ran across suggested looking through the list of G3X LRUs to see if there was something with a compatible connector, and just ordering a kit. But it doesn't look like there's anything useful for the 25-pin Dynon intercom connector.

After looking at the connector kit that came with my GPS-175 today, I'm thinking of just making my own ground block. I've got some 1/8 thick aluminum stock, shouldn't be too hard to cut a rectangular piece and drill/tap a couple holes for ring terminals. I haven't yet conjured up an idea for how to secure this strip, though. Maybe I could epoxy it to the D-sub hood or something. More food for thought.
 
My intercom wiring looks just like the pic from 94KB. Simple and effective. Daisy chain seems overly complicated to me and creates potential issues down the road if you need to dig into the harness for troubleshooting or upgrade. I used something similar anywhere that I have multiple shield grounds that must be ganged and always use green wire for them to help with troubleshooting.
 
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You can get the Garmin connector kits from SteinAir. They are a little pricy but make for a clean installation.

Is there a Garmin connector with the right hood for a 25-pin D-sub? I didn't see anything when I went through all the pinouts in the G3X manual.
 
Since folks have been interested in how this goes, I'll share what I ended up doing. I liked the idea of the aluminum bus bar but was stumped as to how to mount it. I wanted it to be integral to the connector/pigtail, so as not to have yet another thing to disconnect when pulling the panel. Sticking it to the backshell seemed kinda decent but also like it might make servicing the connector a pain.

In the end, I settled on a sort of clamp arrangement. I cut two pieces of 1/8" aluminum stock, about half an inch longer than the width of the backshell. Matched screw holes in both pieces mean that a pair of long #6 screws can clamp the whole shebang around the connector.

One piece has small holes that are tapped for the #6 screws. The idea is that this piece is what the ring terminals attach to; the screws go through the ring terminals and are tightened to the piece of stock. The second piece has larger holes for the screws to pass through. This is how the clamp works; this second piece slips over the screws and gets snugged down with a pair of nuts.

With this in place, the thumbscrews are still accessible so the intercom can be disconnected for service. If I need to open up the backshell, I just have to loosen the two nuts and slide the thing off and out of the way.

First mock-up on the connector to make sure it works:
img_2206-1-1024x768.jpg


I decided to wrap both aluminum pieces in silicon tape as well. The idea here is to help the bus stay in place without having to put too much clamping pressure on the connector.

The finished connector:
img_2208-1024x768.jpg


And from another angle:
img_2209-1024x768.jpg


I want to get some shorter screws to use here just to make this a bit more tidy, but this is functional for now. About the only downside to this setup is that there are only two spots for attaching ring terminals. I suppose you could add another hole or two towards the middle of the bus, but then you've got to carefully split the difference between the screw being short enough to not interfere with the backshell, but also long enough to get good thread engagement.

Another downside to this could be if you don't have the space to the sides of the connector. In this case, the finished ground bus is still slightly narrower than the Dynon intercom unit, but other setups might not be as lucky.
 
Garmin connector kit might work a little better.... their connector/backshells rock!

GAD29CnKt-500x500.jpg
 
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Yeah I agree with Walt. It looks like his pic has the connector you were looking for too. Just to add another comment: the busbar needs to make electrical contact with the outer portion of the connector. I'm not sure if you have it working that way or not from your pics.
 
Ohhh...you know, I think I read the daisy-chain approach when I was looking for other posts like this, but somehow it didn't occur to me exactly how it could work. I was thinking it'd be the same old "one big splice" problem.

But now it occurs to me that for each of my solder sleeves, I can insert more than one ground termination wire, and make this stupidly simple. All the shields get chained together that way, I can also insert the two ring-terminal wires into one as well, and finally have a short pigtail that gets window spliced to the long wire from the intercom ground pin to the ground bus.

Funny how obvious things don't always become obvious until pointed out. Thank you!

Daisy chaining using solder splices is the industry standard and works well for shields. For power grounds or signal grounds, if you combine grounds to a single point, beware of what system failures you might have if the single ground fails. Therefore splitting them to multiple points is advisable.
 
Daisy chaining using solder splices is the industry standard and works well for shields. For power grounds or signal grounds, if you combine grounds to a single point, beware of what system failures you might have if the single ground fails. Therefore splitting them to multiple points is advisable.

Can you elaborate on this? Multiple grounding points seems like you're asking for noise and ground loop complications.
 
Can you elaborate on this? Multiple grounding points seems like you're asking for noise and ground loop complications.

Just limit the number of connections to one ground point but keep the ground points in close proximity. For example the forest of tabs does just that. The block is bolted to the airframe which if done properly is high reliability, but provides multiple independent connections in close proximity. You could also do the same thing with multiple ground studs in close proximity. The standard of choice, AS50881, recommends each ground stud be limited to 3 connections. I have exceeded that in some designs for non safety of flight applications.
 
Just limit the number of connections to one ground point but keep the ground points in close proximity. For example the forest of tabs does just that. The block is bolted to the airframe which if done properly is high reliability, but provides multiple independent connections in close proximity. You could also do the same thing with multiple ground studs in close proximity. The standard of choice, AS50881, recommends each ground stud be limited to 3 connections. I have exceeded that in some designs for non safety of flight applications.

When you said multiple ground points I immediately thought you meant grounds all over the airplane. Forrest of tabs or multiple ground studs right next to each other makes a ton more sense.
 
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