Ground for Lighting

[shuttle]

Hi David,
Thanks for your post. I must admit that instinctively I feel it would be prudent to treat the HID ballast as a special case and run a ground wire for it, as you have.

I appreciate that you have done the same for each component at the wingtip but I'm inclined to ground the 'simpler' components, such as the position lights, locally.

Thanks for the reminder. I had previously read that "Wiring for Smart People" doc and picked up a few things. I particularly liked the idea of using colour coded wiring and have followed that piece of advice. Only downside is that it makes deciding what wire quantities to purchase somewhat more complicated!

[flion]

I had one 'gotcha' with using local grounds, and that was my fuel senders. When I hooked up the resistive senders to my BMA engine pod, it didn't work. Since the pod has a ground connection for each tank, I tried connecting that directly to ground and still no luck. An email exchange with Greg Richter revealed that the airframe ground generated too much 'noise' for the pod to reliably sense resistance, so I isolated the senders from common ground and ran a dedicated ground wire from each sender to the pod. Sure enough, it worked. The only reason I mention this is so that someone whose equipment doesn't work even though everything seems hooked up properly might consider if the common ground may be causing their problem. Most of the time, it will be just fine.

[Mel]

Remember the BMA was designed primarily" for a "plastic" airplane.

[David Clifford]

Originally Posted by Mel

Remember the BMA was designed primarily" for a "plastic" airplane.

That may be so but on occassion the fuel readings in my buddys Cozy will give erroneous readings of remaining fuel on his BM EFIS 1.

[longranger]

Good idea to provide a dedicated ground, especially with the HID's. Even with resistive landing lights, it would be a good to use a dedicated ground wire routed as closely as practical with the supply wire to lessen the probability of stray magnetic fields, making the compass and magnetometer(s) happier.

Yes, commercially produced aircraft have used the airframe for an electrical ground return for years as a manufacturing cost saving, and the electrical components themselves aren't affected, but the compass correction cards in some of those airplanes look like they came out of a random number generator.

(BSEE, University of Tennessee, 1979)

[Dan Blumel]

It is best as much as possible to use twisted pairs when routing the wires. I would not do it any other way for strobe and HID power feeds.

[shuttle]

Thanks for that, Dan,

Regarding the "as much as possible", how far do you go?.......

I take the twisted pair from the HID ballast back to the switch.

Does the ground wire part company with the +ve there at the switch?

Or do you recommend skipping the ground wire around the switch and continuing the twisted pair to the breaker on the busbar?

I.e. How critical is twisted pair wiring on that breaker-to-switch wire section?

[N941WR]

Originally Posted by Dan Blumel

It is best as much as possible to use twisted pairs when routing the wires. I would not do it any other way for strobe and HID power feeds.

FYI - I had originally grounded my strobes at the common firewall ground. You could hear the discharge in my headsets. I then made a ground right next to the central strobe power pack, located under the baggage compartment floor. The power pack ground and the termination for the shield grounds are tied to that platenut. The noise went away with this simple change. Note, the shield ground was not connected at the wing tip but was carried all the way through the wing root to the power pack.

Your mileage may vary.

[Dan Blumel]

Originally Posted by shuttle

Thanks for that, Dan,

Regarding the "as much as possible", how far do you go?.......

I take the twisted pair from the HID ballast back to the switch.

Does the ground wire part company with the +ve there at the switch? Yes, most typically.
Or do you recommend skipping the ground wire around the switch and continuing the twisted pair to the breaker on the busbar? If easily done, this is the ideal.
I.e. How critical is twisted pair wiring on that breaker-to-switch wire section?

Not critical.

[MauiLvrs]

Originally Posted by Mel

No extra ground wire is necessary. Airframe ground is fine for all these applications; nav, landing lights, strobe p/s, fuel gauge senders, etc.
Mel...DAR

Used local ground for the landing lights and pitot heat...
Works great, and simple..