# Methods Of Grounding Aluminum Chassis (etc...)



## ampmadscientist

*This is one of the questions that was sent to my mail box: (I'm going to explain this w/ more details)*

*"This is my first amp build , ongoing.
I admit that I lack much knowledge in this area. However, I'm determined to make this work.
I've been reading the posts concerning aluminum chassis vs steel, and yes, I made the unfortunate blunder to have had an
Aluminum chassis built similair to a Super Reverb chassis. I see that the main issue here is the danger of grounding to the chassis with steel to aluminum, an obviously potential big problem as the aluminum eventually begins to oxidize and then corrode, destroying the ground altogether. Mad scientist, you mentioned something about a steel and aluminum stud... but this confuse's me a bit, since a steel and aluminum stud would still contain these two metals side by side and thus begin the corrosion process. Can you explain what you mean, and what does one of these studs look like?
Also, you mentioned not allowing an aluminum chassis to be a current path, can you clarify this further for me ?,since I need to know exactly how to assemble these things so as not to create a death trap. 
I'm in no hurry to get this amp done, still collecting parts and pieces, but I need a clear vision, and I'm not interested in rushing into a failure. I hope I don't need to acquire a steel chassis. There is a super welding shop down the street which actually fabricated this chassis for me, it's presently undrilled, etc. so there is no danger of me putting this thing together anytime in the near future."*

This post is about electrical safety.

A. First, you CAN use aluminum, but you need to take some precautions to prevent the ground connections from oxidizing and failing.
This is basic electrical knowledge.
All (REAL) electricians are taught the rules for proper grounding of aluminum (chassis or otherwise)...OR connecting aluminum wire in an electrical circuit.

Background: When used as a conductor of electricity, dissimilar metals (such as aluminum and copper) will cause formation of oxides on the surface of the metals.

*This oxide is a perfect insulator, and it will prevent and stop all electrical continuity.*
(in other words, the two metals connected together [OXYGEN IS TRAPPED BETWEEN THE SURFACE OF THE METALS] will cause the electrical connection to fail from corrosion).

B. This problem is most likely to occur when connections are held together with screws, or other methods, which depend solely on metal - to - metal contact...such as rivets...etc...

C. No matter how tight the screws are - it won't stop the oxides from forming.

D. More (in depth) information: (continued)


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## ampmadscientist

6. More information: *"Electromagnetic Compatibility" By Henry Ott
*
http://s1.downloadmienphi.net/file/downloadfile5/192/1388769.pdf
*
(Quote)*
"In addition to producing a noise voltage, the use of dissimilar metals can
produce a corrosion problem. Galvanic corrosion causes positive ions from
one metal to be transferred to the other one. This action gradually causes
the anode material to be destroyed. The rate of corrosion depends on the
moisture content of the environment and how far apart the metals are in
the galvanic series. The farther apart the metals are in the galvanic series, the
faster the ion transfer.
An undesirable, but common, combination of metals is
aluminum and copper. With this combination, the aluminum is eventually
eaten away. The reaction slows down considerably, however, if the copper is
coated with lead-tin solder because aluminum and lead-tin solder are closer in
the galvanic series.
The following four elements are needed before galvanic action can occur:
1. Anode material (higher rank in Table 1-13)
2. Electrolyte (usually present as moisture)
3. Cathode material (lower rank in Table 1-13)
4. Conducting electrical connection between anode and cathode (usually
present as a leakage path)

TABLE 1-13. Galvanic Series.

ANODIC END
(Most susceptible to corrosion)

Group I
1. Magnesium

Group II
2. Zinc
3. Galvanized steel
4. Aluminum 2S
5. Cadmium
6. Aluminum 17ST

Group III
7. Steel
8. Iron
9. Stainless steel
(active)
10. Lead-tin solder
11. Lead
12. Tin

Group IV
13. Nickel (active)
14. Brass
15. Copper
16. Bronze
17. Copper-nickel alloy
18. Monel
19. Silver solder
20. Nickel (passive)
21. Stainless steel

Group V
22. Silver
23. Graphite
24. Gold
25 Platinum

CATHODIC END
(Least susceptibility to corrosion)

Galvanic action can take place even if moisture does not get between the
anode and the cathode. All that is needed is some moisture on the surface where
the two metals come together, as shown in Fig. 1-11.
As observed in Table 1-13, the metals of the galvanic series are divided into
five groups. When dissimilar metals must be combined, it is desirable to use
metals from the same group. Usually metals from adjacent groups can be used
together if the product is to be used in a fairly benign indoor environment.
Other methods of minimizing corrosion between two dissimilar metals are as
follows:
Keep the cathode material as small as possible.
Plate one of the materials to change the group that the contact surface
is in.
Coat the surface, after joining to exclude surface moisture.

1.14.2 Electrolytic Action
A second type of corrosion is caused by electrolytic action. *It is caused by a
direct current flowing between two metals with an electrolyte (which could be
slightly acidic ambient moisture) between them.* This type of corrosion does
not depend on the two metals used and will occur even if both are the same.
*The rate of corrosion depends on the magnitude of the current* and on the
conductivity of the electrolyte.

1.14.3 Triboelectric Effect
A charge can be produced on the dielectric material within a cable, if the
dielectric does not maintain contact with the cable conductors. This is called the
triboelectric effect. It is usually caused by mechanical bending of the cable.
The charge acts as a noise voltage source within the cable. Eliminating sharp
bends and cable motion minimizes this effect. A special ‘‘low-noise’’ cable is
available in which the cable is chemically treated to minimize the possibility of
charge buildup on the dielectric."


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## soundboy57

Have any deaths been reported from using the many early Marshall amps made with aluminum?


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## mickeydg5

Tell the person who sent the email to please comment. Then we can get more dialogue.


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## ampmadscientist

Aluminum Chassis / Steel Chassis:

The ground lugs are attached to chassis permanently, and lugs are solder-able for attaching wires..
You simply attach your circuit grounds as you build the amp.
The only difference is that the grounds no longer depend on screws or metal to metal contact (alone).

The solder (steel) The weld (aluminum) Simply assures that the ground cannot break down from oxygen intrusion OR loose hardware, or other causes (Electrolytic Action, Galvanic Corrosion, etc..)

My favorite ones include: Half Steel - Half Aluminum Stud
The aluminum joins on the aluminum chassis side, but the ground wire does not join to the aluminum.
Also, the steel side can be soldered.

Tig Weld...join ground lugs to chassis before building

Pre Made Grounding Bars made for Joining Aluminum to Steel or 1/2 Copper Half aluminum grounding bars.

But as I said earlier:
It's just easier for me to solder steel or copper to steel instead of going through all the preparation.
All I need is a heat gun, and a BF soldering Iron.





"Exothermic welding, also known as exothermic bonding, thermite welding (TW),[1] and thermit welding,[1] is a welding process that employs molten metal to permanently join the conductors. The process employs an exothermic reaction of a thermite composition to heat the metal, and requires no external source of heat or current. The chemical reaction that produces the heat is an aluminothermic reaction between aluminium powder and a metal oxide...."


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## stickyfinger

So by this theory I can solder the grounds straight to the chassis and wont be plagued by oxide connections?


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## m1989jmp




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## Micky

I just use NoAlOx, works fine and no worries. Ever.


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## Guitar-Rocker

"Exothermic welding, also known as exothermic bonding, thermite welding (TW),[1] and thermit welding,[1] is a welding process that employs molten metal to permanently join the conductors. The process employs an exothermic reaction of a thermite composition to heat the metal, and requires no external source of heat or current. The chemical reaction that produces the heat is an aluminothermic reaction between aluminium powder and a metal oxide...."











No one alive is going to shoot a Cadweld shot on a tube amp, why do you put crap like that up here? To fluff up your posts? (95% of the guys on here don't have the slightest clue what that is, how it works, or the practical applications.


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## Guitar-Rocker

A de-ox inhibitor works to prevent oxidation . Nothing helps this steel.


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## stickyfinger

Terry, I'm actually thinking about welding the ground lugs straight on the chassis LOL !

TO be honest I have a dozen DIY builds out in the field. Past builds I usually sell to fund new builds. I don't have liability.. It does scare me.

I have heard of this issue before. While I don't know if folks ever died from this Id like to prevent problems in the future.
Fusing the HT, switching AC on the standby instead of DC are all modern electrical standards ect that I do and are required.
Nothing wrong with building safer.


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## neikeel

If you use an Aluminium chassis and apply the Larry grounding scheme exactly using serrated washers and brass nuts which are correctly tightened and then seal it with a tamper proof agent (eg loctite) also like look of the stuff that Micky but never felt it necessary. The system has dedicated mains ground (which ideally you label as such). 
I don’t think you will have liability issues.


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## printer

From the author of the book, 



> Tin also provides a low contact resistance and is stable in most environments.
> Tin is so malleable that pressures above about 5 psi do not decrease the
> impedance of the joint. Tin performs almost as well as gold, costs significantly
> less, and is compatible with all environments. Tin is galvanically compatible in
> a seam with, nickel, silver, stainless steel, and aluminum, but not gold.



So tin plated lugs are fine to use on aluminum. The text also says that adjacent groups are ok so aluminum and led-tin soldered connectors are also ok. The corrosion talked about needs a current parring through the joint, if you are real concerned (and I see no reason not to do this) the safety ground from the line cord can be bolted to the chassis and normally there is no current flowing through the joint so therefor no corrosion. Not a good idea to stack this connection with your power supply ground point.


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## Micky

neikeel said:


> If you use an Aluminium chassis and apply the Larry grounding scheme exactly using serrated washers and brass nuts which are correctly tightened and then seal it with a tamper proof agent (eg loctite) also like look of the stuff that Micky but never felt it necessary. The system has dedicated mains ground (which ideally you label as such).
> I don’t think you will have liability issues.


My first exposure to Noalox was installing electrical entrances into new homes. Aluminum wire is commonly used, and the electrical entrance generally has copper or some sort of plated conductor buss material. With up to 200A @ 120VAC running thru it, I would imagine that you aren't gonna see more current than that.

I have never, ever seen a corroded entrance using this method. As long as you aren't running any current thru an aluminum/copper connection I can't really see the concern. NEC has specific guidelines for this.


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## ampmadscientist

Noalox is specifically made for aluminum to aluminum connections only.
It is not intended for mating dissimilar metals...nor is it approved for such usages.
Aluminum has been banned for internal residential wiring...FYI.

The service panels that (were) used for aluminum wiring had aluminum terminals, the Noalox was used for aluminum to aluminum contact only on approved devices. (devices made out of aluminum)

It was never designed for copper / tin / steel to aluminum connections.

"I have never, ever seen a corroded entrance using this method."

Corroded entrance is quite common.


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## stickyfinger

So MAS what is your opinion of soldering the ground lugs straight to the chassis? (might be a PITA)

What about welded?

I like keeping things original and I like the hum and noise it might create. Its part of the tone of the old amps and don't want to "fix" it


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## Guitar-Rocker

I get so tired of all this incorrect dribble any time someone mentions the word "aluminum", and then MAS injecting his interpretation of what he thinks is correct. What MAS has said about aluminum wire in a residence only is correct in reference to branch circuit wiring, your lights and receptacle type circuits and reference to aluminum wiring being used in totality is incorrect...….Yes aluminum service entrance cable is permissible for residential homes.


*National Electric Code Tables 310.15 B6 and 310.16 specify that 2/0 gauge copper wire can be used for service or feeder connections to a 200-amp panel.* The source lists 4/0 gauge aluminum wire as another acceptable option.

And electrical service panel buss material is not aluminum, rather it is tin coated copper. Reference Square D load center specs. If a connector is "listed as CU/AL you can use aluminum in that connection, if permitted by code. 

Also here is the real information about aluminum. The restriction on aluminum for residential wiring was for branch circuit wiring. This was a two part reason. First was due to the amount of physical stress on a small aluminum conductor such as in romex that broke easily if bent too far. The second was the device (ie the outlet receptacle was not rated for CU/AL connections). That is the real truth.

For those who wonder about aluminum in the electrical field, read this:

http://www.aluminum.org/resources/electrical-faqs-and-handbooks/electrical

I am retired, and served during my career as a Electrical Journeyman Lineman, then Electrical Industrial Electrician and a Master Electrician for over 40 years, I can speak from experience.


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## Micky

I think everyone here realizes he is a douche-bag who thinks he knows it all. It is plainly obvious he doesn't...


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## stickyfinger

AMS-

What exactly needs to be tied to one ground lug? 
For *SAFTY ONLY *disregarding modern ground loop suppression methods. 

1. Power transformer grounds?
2. Power valve grounds?

3. Filter cap grounds??

4. Earth??? 
I see this not mentioned and usually with its own ground point. 
This need to be on the same ground so every thing can divert back to earth in case of failure, correct?

What else??

I'm into modern safety practice, asked this once before and never got a reply.


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## printer

If you can make it to the bottom of the page without your eyes crossing I applaud you. 

http://www.diyaudio.com/forums/diya...udio-component-grounding-interconnection.html


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## Gunner64

If everything goes back to the cans, and the cans are tied to the same ground point as the main ground, not using the chassis for this path, wtf is the difference if the chassis is aluminum or steel? I'm not a trained tech but seriously, what does it matter if the chassis is not depended on for this ground?


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## stickyfinger

SO..

I ask AMS 2 legit questions about this topic as I'm genuinely interested in modern safety and doesn't respond to either. I'm really starting to believe the OP doesn't understand or grossly misunderstood what the hell he read.


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## ricksconnected

.


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