How many grounding blocks?

[BillL]

Originally Posted by rightrudder

Thanks. I like the simplicity/straightforwardness of back-to-back FOTs. I'm using LED strobe/position lights, which will be shielded, but will probably go with local ground for landing light. Question: Shield gets grounded at FOT, and negative wire on strobes is grounded at the same FOT?

I read somewhere that is was possible to use the shield as the ground wire itself--dubious advice from a noise perspective?

If you are going to use a standard incandescent light local ground may be fine, but high voltage lighting, or LED lighting there are power electronics and that can be an issue. I ran grounds for everything but the ELT back to the FOT. When the ELT is needed I don't care about ground loops and harmonics.

I can not imagine you not moving to more modern, long lasting lighting.

[bruceh]

I have all of my grounds going to the same forest of tabs, except for my LED landing lights and an LED baggage light. No issues with noise or interference so far!

[N941WR]

Originally Posted by rightrudder

... Question: Shield gets grounded at FOT, and negative wire on strobes is grounded at the same FOT?
...

Here is what worked for me, YMMV.

I clipped the shield at the light and continued it all the way to the same grounding platenut I used for the power pack.

I was warned not to ground it at both ends as it will create a "loop". So, I added connectors for the shield wire at the wing root and connected it there.

Again, this is with "traditional" strobes. I didn't think those new fangled LED strobes required shielding but if you have it there, I would probably treat them the same as I did with the strobe pack.

[rightrudder]

Thanks, guys. I have LEDs for everything but I don't want to take any chances, so bring on the shielding!! I've got a terminal block under the control-stick covers to connect all three strobes, so one of the terminal strips will carry the shield ground (which will ultimately be grounded at the firewall FOT).

So my question is: Should I separate both the "shield ground" and the "normal ground" and run both all the way to the firewall? (Two separate ground connections all the way through?) I certainly will ground only the firewall end of the shield.

Just trying to get this through my thick head!

[maus92]

On an RV-8, the firewall is separated from the panel by the forward baggage compartment, so what are builders doing with the FOT grounding block? If you use the thru bolt style, the hot side of the FOT is on the engine side of the firewall, and the cold side ends up in the baggage compartment, and not the more convenient location behind the panel. Do people just use a single sided FOT on the firewall, and run a fat jumper to an insulated secondary FOT behind the panel?

[billdianne]

Originally Posted by maus92

On an RV-8, the firewall is separated from the panel by the forward baggage compartment, so what are builders doing with the FOT grounding block? If you use the thru bolt style, the hot side of the FOT is on the engine side of the firewall, and the cold side ends up in the baggage compartment, and not the more convenient location behind the panel. Do people just use a single sided FOT on the firewall, and run a fat jumper to an insulated secondary FOT behind the panel?

That's what I did. On the firewall I just used a single bolt and ran a wire to the FOT on the baggage compartment wall. Used shoulder washers and a piece of plastic cut to the shape of the FOT and mounted on the instrument side of the baggage compartment wall.

[AAflyer]

OK, now I'm a little unsure.
I currently have my FOT in my -8 on the instrument bay side of the baggage compartment bulkhead?conveniently located for all my avionics. I thought I was "good to go", as it is securely grounded to this bulkhead with two screws with tooth washers.
Now I'm reading above, that I need to 'insulate' this FOT, and add a wire to another grounding point in the engine compartment??
Why?

[maus92]

Originally Posted by AAflyer

OK, now I'm a little unsure.
I currently have my FOT in my -8 on the instrument bay side of the baggage compartment bulkhead?conveniently located for all my avionics. I thought I was "good to go", as it is securely grounded to this bulkhead with two screws with tooth washers.
Now I'm reading above, that I need to 'insulate' this FOT, and add a wire to another grounding point in the engine compartment??
Why?

If you mount the panel FOT to metal, that sets up the potential for a ground loop if you already have a firewall grounding point - which is what you are trying to avoid with FOT.

I am running a grounding strap from a rear crankcase bolt to a brass bolt installed on the firewall that also penetrates a framing member. Also attached to the bolt is the battery negative cable, and a cable that runs back to the panel FOT - which is insulated from the aircraft body/metal as described earlier. Electrically, the firewall brass bolt becomes the single point ground, at least in theory.

[cdeerinck]

Being an electronics newbie, I don't mean to argue, I just want to learn as well.

I was just going through this last night, and was reviewing docs on the AeroLEDs site. They explicitly call for 3 conductor 20awg shielded wire, and the nav/strobe doc states "to avoid interference, connect ground to the airframe close to the light". It also says to ground the Sheilds at both ends.

And lastly, that wire leaves no room for a home run ground, nor is it large enough to do that. For the strobe (the biggest pulse generator), 20awg at 3 amps is about 1 volt drop in 18', so running a ground wire would mean that needs to become a much bigger wire, out and back for the strobe, because that makes it a 36' circuit.

Trust me, I like the smaller wire in the wing, or else I am out of grommet space.

Can anyone help me understand why AeroLEDs recommends what they do?

One last question: I am putting a plug at the wing root, to allow me to get as much done as possible, before final assembly. What is the best connector type and method to carry the shielding through that connector? My setup is nearly identical to the author of this thread: in one wing AP servo, landing, and nav/strobe, and in the other heated AOA pitot, and matching lights.

I wish there was a permanent thread like "Show us your panel", but instead called "Show us your wiring", with people also reporting pictures, issues, or lack thereof.

As a "for what it's worth", I was planning on putting my two sided FOT on the firewall, far left (when looking forward), just under the baggage shelf. That puts the wiring out of the storage area, but still on the firewall, and keeps it out of sight while flying. Someone please tell me the IO-360 starter is on the left...

[maus92]

Originally Posted by cdeerinck

Being an electronics newbie, I don't mean to argue, I just want to learn as well.

I was just going through this last night, and was reviewing docs on the AeroLEDs site. They explicitly call for 3 conductor 20awg shielded wire, and the nav/strobe doc states "to avoid interference, connect ground to the airframe close to the light". It also says to ground the Sheilds at both ends.

And lastly, that wire leaves no room for a home run ground, nor is it large enough to do that. For the strobe (the biggest pulse generator), 20awg at 3 amps is about 1 volt drop in 18', so running a ground wire would mean that needs to become a much bigger wire, out and back for the strobe, because that makes it a 36' circuit.

Trust me, I like the smaller wire in the wing, or else I am out of grommet space.

Can anyone help me understand why AeroLEDs recommends what they do?

One last question: I am putting a plug at the wing root, to allow me to get as much done as possible, before final assembly. What is the best connector type and method to carry the shielding through that connector? My setup is nearly identical to the author of this thread: in one wing AP servo, landing, and nav/strobe, and in the other heated AOA pitot, and matching lights.

I wish there was a permanent thread like "Show us your panel", but instead called "Show us your wiring", with people also reporting pictures, issues, or lack thereof.

As a "for what it's worth", I was planning on putting my two sided FOT on the firewall, far left (when looking forward), just under the baggage shelf. That puts the wiring out of the storage area, but still on the firewall, and keeps it out of sight while flying. Someone please tell me the IO-360 starter is on the left...

AeroLEDs use a "switched" internal circuit design, which can cause noise in audio circuits if not properly shielded - hence their very specific wiring instructions (Whelen Orion 600 LEDs use an unswitched design that does not require the use of shielded wire, although I did anyway.) Grounding a shielded wire on both ends is generally a no-no - particularly with avionics audio equipment and jacks - but should not pose a problem with LEDs. Grounding the far end nearest the light to the airframe is OK. As far as the end nearest the switch / panel, you *could* extend the shield conductor to the FOT with an unshielded wire if you want, but keep it as short as possible - 20AWG would be fine. Alternatively, some people wire their switches with a common ground buss wire/bar for all the switches, using a single larger diameter wire run from the buss to the FOT. In this case, you could connect the LED shield to the switch common buss, and not have to extend a wire to the FOT.

As far as the wing roots break, I used a Molex / nylon connector. Just remember to keep the exposed wires at the connector as short as possible, and use solder sleeves and a pigtail for the shield conductor. Steinair has a YouTube video showing how to use them.

I don't have a need for the engine side FOT, so I don't have the double sided FOT. As for placing the panel side FOT on the firewall left side under the baggage shelf, that could be done. Just remember that you will have many ground wires running to the FOT, so have a way to organize and secure those wires so they don't interfere with the rudder pedals and brake lines.

I don't know about the starter on the IO-360, but on the O-360, the starter is on the left side facing forward, with the alternator on the right.