Combining grounds for several circuits

[brenegan]

I'm thinking of combining grounds for several circuits and running one
ground back to a forest of grounds behind my panel; namely landing and position lights and pitot heat. I was reading 43.13b chp 11 sec 5 and only
found references about single point of failure, but no other recommendations unless I missed something. I know about using the airframe for ground and running individual grounds. Any Opinions about this being a totally wrong thing to do?

[N941WR]

David,

The lights are not a high noise application, so you could probably get away with it.

On my -9 I riveted a plate nut on the outboard wing ribs and grounded the position and landing lights out there. Everything else, with the exception of the strobes (documented on my web site) were run back to the common ground on the firewall.

Regarding the single point of failure thing...

Should that wire break, it won't comprimise the safety of your flight, other than landing without a landing light and we (at least I was) were trained to do that back when we were getting our PPL's.

[grover]

I'm doing much the same thing, with at least 2 different large conductors (one to airframe, one to batt -) to ground for redundancy.

[AlexPeterson]

Loads out in the wing or tail that are not noisy should simply use the airframe as ground. Just fasten the ground wire to a loop connector, scratch the primer/anodizing off, and bolt with a star washer.

I guess there is only one airframe, so no redundancy though....

[N941WR]

Originally Posted by grover

I'm doing much the same thing, with at least 2 different large conductors (one to airframe, one to batt -) to ground for redundancy.

James,
This may introduce noise into the system, if a ground for one circuit goes to both locations.

[longranger]

Originally Posted by brenegan

I'm thinking of combining grounds for several circuits and running one
ground back to a forest of grounds behind my panel; namely landing and position lights and pitot heat. I was reading 43.13b chp 11 sec 5 and only
found references about single point of failure, but no other recommendations unless I missed something. I know about using the airframe for ground and running individual grounds. Any Opinions about this being a totally wrong thing to do?

Just make sure that the one ground wire is large enough to carry the TOTAL current for all circuits for which it is serving as a return. Pitot heat and landing lights are pretty power-hungry. Also, you'll have lower stray magnetic fields (affects heading instrumentation) if the return wire follows the supply wire fairly closely.

Miles

[brenegan]

Originally Posted by longranger

Just make sure that the one ground wire is large enough to carry the TOTAL current for all circuits for which it is serving as a return. Pitot heat and landing lights are pretty power-hungry. Also, you'll have lower stray magnetic fields (affects heading instrumentation) if the return wire follows the supply wire fairly closely.

That was my plan... size it accordingly and run it back in the same conduit.

[az_gila]

Originally Posted by N941WR

James,
This may introduce noise into the system, if a ground for one circuit goes to both locations.

Yes... but not with the specific circuits mentioned... gil A

[longranger]

I'm not sure how pitot heaters control temperature, or even if they do. If they are full on all the time, or have proportional control of the current, they will not induce a siginficant amount of noise. If however they have an ON/OFF thermostat, they would generate some electrical noise.

[jonbakerok]

Why would you run ground wires when the entire airframe is made of aluminum? Did you read somewhere that the airframe is a bad ground?

Take it from a former Air Force avionics technician. Wires break and they're a bitch to troubleshoot. So if you use the airframe for your ground, right off the bat you eliminate half the wiring in your airplane. How can that not be a good thing? Not to mention the weight you save.