Galvanic Corrosion Electrical Work

[Mikegh]

Where does galvanic corrosion arise in electrical work ?
Is it mostly copper-aluminium or are there other metal combinations to watch out for ?

 

[pc1966]

Most metals with aluminium cause corrosion if any damp present, since Al is so high on the reactivity list (at least, of metals you typically encounter in electrical work). How bad it is depends on the difference in electrode potential:

Galvanic series - Wikipedia

en.wikipedia.org

Zinc plating / galvanising is designed so the coating sacrifices itself to protect the base metal, such as steel, for corroding itself. Zinc is OK with aluminium, but most other metals such as stainless steel, brass and copper really go for it. Same applies if you have, say, a brass fixing on galvanised metal - it will accelerate the loss of the plating.
Here is a chart showing what is a good mix (white) and what to avoid (red):

In practice you can't always avoid bad combinations so the next-best option is to exclude water+oxygen from the joint so it is not corroded.
You can use lubricating grease on mechanical fasteners, in fact you generally always should, especially on stainless that is prone to galling. But for electrical work you don't want any extreme-pressure lubricants that stops metal-metal contact for obvious reasons! Here you can get special compounds for aluminium use such as Noalox / Penetrox which have (I think) metallic zinc particles in them, but Vaseline is a good option for general use, so long as not high temperature. Traditionally that was used on car battery terminals to avoid corrosion issues.

 

[nicebutdim]

Zinc plating / galvanising is designed so the coating sacrifices itself to protect the base metal, such as steel, for corroding itself. Zinc is OK with aluminium, but most other metals such as stainless steel, brass and copper really go for it. Same applies if you have, say, a brass fixing on galvanised metal - it will accelerate the loss of the plating.

Odd that we regularly use brass bushes with galv conduit fittings.

 

[pc1966]

Odd that we regularly use brass bushes with galv conduit fittings.

Fine what it is dry!

I guess for outdoor use, etc, the plated steel ones would be better. But #1 rule is keep it lubricated if you ever want to change it in the future.

 

[westward10]

Odd that we regularly use brass bushes with galv conduit fittings.

The threaded part is generally not galvanised.

 

[nicebutdim]

But #1 rule is keep it lubricated if you ever want to change it in the future.

Good advice in general.

 

[nicebutdim]

The threaded part is generally not galvanised.

Would cheap couplers be threaded after galvanising? Never paid much attention to what goes on inside, but will have to take a look now.

 

[westward10]

Never seen a coupler galvanised internally.

 

[Mikegh]

Thanks pc1966 for the very comprehensive reply

 

[Mikegh]

I'm getting more confused now
What type metal are regular electrical lugs made from?
And what type lugs should connect copper cable to galvanized steel ?

 

[pc1966]

Most crimp lugs are copper with a tin plating. If used on galvanised steel anywhere corrosion is likely (wet/damp, especially in salty or industrial locations) then put a thin smear of Vaseline between them before assembly and you won't see any issues.

 

[Mikegh]

What's the idea behind putting Vaseline between them ?
Would it not be around them ?

 

[pc1966]

What's the idea behind putting Vaseline between them ?
Would it not be around them ?

You could put it all around an assembled joint, but if you apply first and then assemble you get it filling all of the tiny cracks and surface imperfections to keep the moisture out. The worst corrosion tends to be closest to the metal-metal joint where they differ, so by making sure that is covered at a microscopic level you get better protection.

Covering with any sort of grease, or even a spray with WD40, etc, afterwards will help keep moisture off. It is the flow of ions within any moisture that is responsible for the effect, hence why it is far worse if the moisture has salt (near sea) or chlorine (near swimming pool), etc, dissolved in it.

 

[pc1966]

To be fair, chlorine will eat away at most things without any other help!

 

[freddo]

To be fair, chlorine will eat away at most things without any other help!

Swimming pool plant rooms are a nightmare!

 

[pc1966]

Swimming pool plant rooms are a nightmare!

It is probably the most corrosive thing you are likely to encounter outside of an industrial process site. There are far, far, worse reagents out there, but they are rare. In fact, some chemists have even blogged about stuff they would chose not to work with:

Science | AAAS

www.science.org