Grounding an aluminium chassis?

[Eythor]

I recently came across a post on a different forum regarding grounding when using an aluminium chassis. The argument was that the common way of using solder lugs and bolting them down, relying exclusively on a mechanical connection, is not safe, as the surfaces will oxidise over time.

That's how I've done things so far on my own builds, and for my own personal use, I don't see this as much of an issue. But, since there is a possibility of my amps ending up in the hands of players with no technical knowledge, I want to do this properly, to avoid potential safety hazards. So, I have a few questions:

1. How likely is it that a mechanical connection between a solder lug and aluminium chassis will oxidise and fail within, say, 10 or 20 years?

2. Is this a genuine danger in the context of guitar amplifiers, or more of a theoretical one?

3. Do any of the "big guys" do it this way?

4. I've come across zinc plated aluminium chassis. Is it possible/safe to solder to the zinc plating of those?

[WimWalther]

1. How likely is it that a mechanical connection between a solder lug and aluminium chassis will oxidise and fail within, say, 10 or 20 years?

Depends on your location.. temperature, humidity, salt air, etc. But generally, if you clean up the lug contact area, and tighten down the lug mounting screw hard enough to create a gas-tight connection, you should be just fine.

[66Strat]

The problem arises because of the galvanic reaction between the aluminum chassis and the steel solder lug. Galvanic reaction causes corrosion to form and the electric connection to deteriorate/fail over time. Strategies to improve the connection include; a star washer to assist in the mechanical connection and a dielectric grease to prevent corrosion. The dielectric should be wiped on and wiped off (bow to Mr. Miyagi) to leave a thin coating on all components; chassis, washer, and solder lug.

[Eythor]

The problem arises because of the galvanic reaction between the aluminum chassis and the steel solder lug. Galvanic reaction causes corrosion to form and the electric connection to deteriorate/fail over time. Strategies to improve the connection include; a star washer to assist in the mechanical connection and a dielectric grease to prevent corrosion. The dielectric should be wiped on and wiped off (bow to Mr. Miyagi) to leave a thin coating on all components; chassis, washer, and solder lug.

Thanks! I'll look into that.

[CrocMule]

The problem arises because of the galvanic reaction between the aluminum chassis and the steel solder lug. Galvanic reaction causes corrosion to form and the electric connection to deteriorate/fail over time. Strategies to improve the connection include; a star washer to assist in the mechanical connection and a dielectric grease to prevent corrosion. The dielectric should be wiped on and wiped off (bow to Mr. Miyagi) to leave a thin coating on all components; chassis, washer, and solder lug.

Galvanic corrosion can destroy electrical connections, but aluminum and zinc are right next to each other on the galvanic reaction scale, so very minimal reaction, if any.  Steel hardware is mostly galvanized with zinc compounds.  You'd probably be fine with no dielectric grease in most environments, but 66Strat does have a good point.  Galvanic reaction between dissimilar metals is something to be aware of -- no copper to aluminum connections without dielectric for sure.

https://galvanizeit.org/design-and-fabrication/design-considerations/dissimilar-metals-in-contact

Aluminum oxidizes instantly in open air.  Electricians use NOALOX -- cuts through the AL oxidation (with zinc particles).  This is something you don't want to wipe off until there's just a thin layer, or you'll wipe off the magic zinc.  Wipe off the excess after tightening the connection.  For this application, a 1/2 oz tube will last a long time.

https://www.idealind.com/us/en/shop/noaloxr-noalox.html

Best,
Russ

[tubeswell]

Or, you can periodically remove the steel lug from the chassis and clean the surfaces. You only need to do that once every 10 years or so