Can we talk about how everyone miswires 28V DC ground loops?

I keep seeing guys at the hangar in Atlanta daisy-chaining grounds on avionics racks like it's a christmas tree. Had a G1000 install last month where the installer tied three units to one lug and wondered why the radios had alternator whine. I've been doing this for 12 years and I've never had a ground loop issue because I run each unit's ground back to a star point on the bus bar. Why do people think it's okay to pile them up? Anyone else have a blown radio from this shortcut?

2 comments

2 Comments

beth_hunt10d ago

Hang on, I gotta push back a little here. Respectfully, daisy-chaining three units to one lug isn't really the same as a proper ground loop in the way most people think. The real problem with that install is probably the contact resistance and the shared path for the return current, not a loop. I've seen guys use a star point on the bus bar too and still get whine if the ground bond to the airframe is rusty or painted over. The radio whine comes from that noisy AC ripple on the main ground cable, not from the stack of lugs itself. Also, if your bus bar isn't isolated from the airframe correctly, you're just moving the problem to a different spot.

eric_johnson10d ago

Hell yeah, finally someone who gets it! I had almost the exact same thing happen on a King Air panel I helped with back in 2019. The guy before me had stacked four ground lugs on one stud, and the radio would cut out every time the strobes were on. I spent a whole afternoon fixing it, running each ground back to the star point like you said, and all the noise just disappeared. But what beth_hunt said about the rusty ground bond is totally on point too - I've seen a star setup fail because the bus bar mounting screw was painted over and nobody scraped it clean first. It's almost like there's no single magic fix, you gotta check everything from the lug stack to the airframe bond or you're just chasing your tail.

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