Grounding

Brambo · #1 02-11-2007, 10:30 AM

Just after the light bulb over my head came on, and I thought I had the concept of grounding understood, I read something that turned that light right off again.

In Ron Alexander?s Electrical System article (Part 2) he talks about the difference between grounding through the airframe and using a grounding bus. What confused me was where he suggests that the grounding bus should be connected to the engine block and from there to the battery. My question is ? If you?re using a grounding bus and all electrical equipment is grounded via the bus, then why do you need to go through the engine block? Why not just wire from the grounding bus direct to the battery?

The fact that I even have to ask this question is what makes me think I'm still am confused about this grounding stuff?.

Bill Rambo
RV7A

Yukon · #2 02-11-2007, 10:40 AM

Because the engine mount rubber dampeners make it difficult for the starter to find a ground.

Geico266 · #3 02-11-2007, 10:46 AM

Maybe it has to do with noise & interference?

jcoloccia · #4 02-11-2007, 10:53 AM

Yukon's got it right. There's a bunch of stuff that hangs off the engine and needs ground. Also, it's just good practice in general to have all the metal in your plane (as much as practical) at as close to the same potential as you can get it. It'll mitigate issues later on with wacky sensor readings and weird stuff like, "The radio only makes this buzzing noise when the door is open, the seat is in the second notch and Mercury's in Jupitor's ascending crecent with a conjugated Martian tidal proxy", or something. Nothing specific. Just good practice.

dan · #5 02-11-2007, 11:04 AM

Consider stress & strain on the battery terminals. The last thing you want is for the wire or wires that are connected to the battery to be able to MOVE at all.

By using a grounding block, you effectively relocate the point of stress & strain OFF the battery. I'm talking about the engine side of the firewall.

mark manda · #6 02-11-2007, 11:08 AM

FAA is concerned with grounding too.

Just received a mandatory Airworthiness Directive to have grounding straps inspected and or replaced.

Reason, just what you said, wacky intermittent electrical problems, poor performance. IIRC

Geico266 · #7 02-11-2007, 11:16 AM

I had a composite plane and ground was a REAL issue there.

Ground to the engine makes sense to relieve stress from the battery post.

Brambo · #8 02-11-2007, 12:41 PM

Quote:

Originally Posted by jcoloccia

Yukon's got it right. There's a bunch of stuff that hangs off the engine and needs ground. Also, it's just good practice in general to have all the metal in your plane (as much as practical) at as close to the same potential as you can get it.

OK, that all makes sense. Thanks for all the replies.

Bill Rambo
RV-7A