Bi-metal lugs or transition plates - when to use

[electricnewbie123]

Is it a common practice to install bi-metal lugs or transition plates n all cases where there are connections between copper and aluminium elements? Or is there an assessment be made in relation to the environmental conditions the equipment is subject to?

The reason I ask is that I noticed some indoor installations (within the room that is free from pollution, in general) where copper cables are connected to aluminium busbars in transformers, without use of any bimetal lugs or transition plates. I just wanted to gather people's opinion on whether it is going to be a headache in future. My common sense suggests that since the room is generally well ventilated, condensation and corrosion will be extremely unlikely.

Your opinions?

 

[waross]

A common procedure.
Aluminum rapidly forms an almost invisible and insulating film of aluminum oxide.
Clean the aluminum very well with a wire brush or a buffing wheel.
Immediately apply an anti-corrosion compound such as Penetrox or No-Alox.
If you are doing a number of connections, apply the anti-corrosion compound to each joint surface as soon as it has been cleaned.
DO NOT clean all the joints before starting to apply the anti-corrosion compound.
Time is of the essence.
If a joint is partly cleaned and you take a coffee break, start over when you return.
Once the joint surface has been covered with the anti-corrosion compound, It may be left for several hours before the joint is made up.
NOTE: Due to the rapid formation of the insulating film on the surface of aluminum this procedure should be followed for all aluminum joints;
eg;
Aluminum to Aluminum.
Aluminum to Aluminum alloy.
Aluminum to Copper.
Aluminum to a bi-metal transition piece.
Aluminum cable to crimp type lugs.
Aluminum cable to setscrew type lugs and terminals.
You are indoors. Aluminum to Copper connections subject to rain water are a corrosion issue for another day.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[electricnewbie123]

Thank you waross.... The jointing compound has been applied in my case - the key doubt I have is whether it is common practice to have transition plate or bimetal lug in ALL copper to aluminium power cable connections or only in cases when there is a concern of corrosion due to moisture...

 

[waross]

I can't recall seeing transition plates used. Even outdoors, some utilities use copper drops from pole mounted transformers to the secondary aluminum distribution cables.
Rain (which these days is acid rain the world over) will react with the copper to form salts that are corrosive to aluminum.
This issue is addressed by making the connections so that the copper conductor is below the aluminum conductor.
But be patience. Hopefully someone who has used transition plates will post in.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[electricnewbie123]

Thank you waross...

Will wait...