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Required ground wire gauge

ArVeeNiner

ArVeeNiner

Well Known Member
Hi all:

I'm presently wiring my RV-9A project...specifically from the switchs to the landing lights. I'm using 16 AWG wire for the positive but can I use smaller gauge (like 18 AWG) for the ground? The reason that I ask is that I'm a few feet short using the 16 AWG but I have plenty of 18 AWG. It would seem to me that there is a voltage drop downstream of the lights which could negate the need for a return of the same size as the hot wire.

Thanks

Kelly Johnson
RV-9A fuselage wiring
San Jose, CA
 
The return wire carries the same current as the supply wire. It does affect the voltage drop too. Think of it as 3 resistors in series: supply wire is R1, lamp is R2, return wire is R3.

Guy
 
Kelly, yeah, like Guy said: Ampacity of the wire is what matters. Most of the wire you'll use is good for voltages much higher than you're using, but the ground wire carries precisely the same current as the hot wire. If 18ga wire would be good for the supply, you can use it for the ground even though you used 16ga for the supply; otherwise, you'll need to use 16ga.
 
Thanks for the info.

I guess I need to send an order to Aircraft Spruce for some 16 gauge. I think I'm now in my "one order per week" stage of the project!! :)
 
Your ground wires should be relatively short. It is acceptable to double up on the grounds and use 2 18ga. wires in parallel.
 
Ahh, that's a good idea (doubling up of wires). I didn't think of that.

I guess I was planning to ground the landing lights to the ground block on the firewall. I would, however, think that landing lights wouldn't be a big contributor to ground loops. Is that a correct assumption? If they are not a big worry then I could ground the lights locally in the wings.

Thanks
 
Kelly,

Ground the wires close to the light in the rib. Lights are not a big contributor to loops. Mine have worked perfectly this way,

Allan
RV-9A + H-6
 
ArVeeNiner said:
Ahh, that's a good idea (doubling up of wires). I didn't think of that.

I guess I was planning to ground the landing lights to the ground block on the firewall. I would, however, think that landing lights wouldn't be a big contributor to ground loops. Is that a correct assumption? If they are not a big worry then I could ground the lights locally in the wings.

Thanks
Click to expand...
Airframe ground will carry more current than any wires. No ground loop problems with lights. They carry a constant current.
 
ArVeeNiner said:
Hi all:

I'm presently wiring my RV-9A project...specifically from the switchs to the landing lights. I'm using 16 AWG wire for the positive but can I use smaller gauge (like 18 AWG) for the ground? The reason that I ask is that I'm a few feet short using the 16 AWG but I have plenty of 18 AWG. It would seem to me that there is a voltage drop downstream of the lights which could negate the need for a return of the same size as the hot wire.

Thanks

Kelly Johnson
RV-9A fuselage wiring
San Jose, CA
Click to expand...

As was stated in several previous posts....the goeszata are equal to the goesintas.
I wouldn't double up on the 18ga wire for the return..It will work fine but looks amateurish and not in keeping with good practice....
 
airframe ground

Use airframe as ground. Saves wire, saves weight, money, and eliminates possible problems.(kiss principle) It is surprising how much wiring you have going up behind the panel anyway. :)
 
Short ground run

If you ground the lights to the airframe in close proximity to the lights you could get away using 18ga for such a short run. Keep the length a foot or less and you will be fine.

If you go that close you probably have a short length of 16ga in your scrap pile!! That way you could keep it looking the same.

As the wire gets longer it needs to be larger guage to carry the amps. Check your Vans wiring chart and you will see what I mean.

No need to run the grounds for landing lights to the ground bus. Airframe is fine.

Ted
 
The voltage drop in the thinner but shorter wire will be off little concern. The main concern is that the wire will run hotter. That is what you have to worry about.

Doubling up on the wire effectively decreases the wire guage by 3. That is, two 18 gauge wires in parallel is equivalent to a single 15 guage wire. Two paralleled 22 guage wires is the same as a single 19 guage wire.

I see nothing wrong with doubling up on the wire. It is done in military aircraft all the time.
 
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