Connection Between Aluminium Cable and Copper Bus Bar

Bimetallic lugs are avaialble, here is one link...google will give you many more, specific to where you live.

http://www.marslug.com/mcl.htm

GA to you.

A comprehensive answer from an expert in that field.

Out of curiosity, i ask : someone told me that he used bimetallic strips between Cu and Al only for outdoor applications. Not for indoor. Here he would ensure vigorous wire-brushing of the Al to take off the oxide coat and immediately (in seconds) cover the surface with oxidation-preventing grease/jelly/compound and quickly make the joint. (Same care in outdoor too, between Al and the Al side of the strip)

Makes sense to you ?

You must also remove the oxide layer immediatly before applying the anti corrosion compound. A wire brush is perfect.

Hi Soebfatehi (& everyone else),

I am trying to electrically join two 6061 Aluminium busbars together (can't permanently join them). They are 15mm x 3mm and are carrying about 50 amps at up to 120 volts DC.

Is it enough to use some corrosion inhibiting paste as you speak of, and then fasten them together tightly with a M8 steel bolt and nut through a hole in each busbar?

If so then could you please be more specific as to what type of paste I should ideally be using?

This is part of a Li-ion battery pack in a solar car.

Regards,

Clint

Of course I will prepare the bolted surfaces by sanding / wire brushing immediately before.

use the paste recommended by me above - or use petroleum jelly or any conducting grease - idea is to exclude atmospheric action wherever possible

sorry - had missed your question - saw it just now and hence responded now

I'm not sure about this particular size, but there are lugs that bear a dual Cu/Al designation. They may require the use of an anti-oxidant compound, and there may be specified screw torques for the connection. Please read carefully the manufacturer's instructions and the local code requirements.

I remember having read in a cable lug manufacturer's catalogue about Copper Terminal Lug for crimping on to an Aluminium Conductor. I think the make is Dowell's. Pl. do a search.

Yes.

Copper lugs for aluminum conductors are available. They are very expensive. These are recommended in certain places where space constraints apply. The surface areas of the palms available for transfer of current to the copper busbar are smaller than in aluminum lugs. This sometimes results in higher temperatures at joints - though not always necessarily so.

All the precautionary measures listed by me for minimizing corrosion at bimetal interfaces apply when those lugs are used.

I have used standard copper lugs on aluminium conduits in lots of heavy current equipment so long as the correct gritted sealing compound is used in the lug housing.I would not consider them to be that expensive.

They perform very well and i have not had one failure.

Copper lug clamped to a copper bus bar is preferable to aluminium lugs, usually buss bars and lugs are tinned to provide a corrosion free connection, but it is still good insurance to smear the conducting faces with a very small amount of compound. Take care not to get it on the threads as this will alter the torquing values.

lock nuts are preferable to locking washers and will retain the tension better than star or spring washers which can release tension due to heating and cooling of the joint.

I was under the impression (perhaps wrongly so) that the biggest problem and earliest failure mechanism with an Al to Cu interface was the difference in thermal expansion, not corrosion. I am not an expert by any means in this area (my disclaimer).

yes differences in the coefficients of linear thermal expansion are another complication.

however the temperature rise and the surface areas are small (in the case of lugs sitting on busbars) to matter substantially. CUPAL washers when used take care of that effectively because very thin fused layers of Cu and Al have sufficient mechanical properties to handle that difference in expansion.

corrosion issues are always there whenever dissimilar metals are in contact because of differing galvanic potentials of substances. if special corrosion inhibiting compunds are not easily available then at least application of petroleum jelly also helps. the most important funda is to exclude or minimize contact with atmospheric gases that give rise to corrosion.

Cut one hole and use the copper screw and nuts.

Bigfamous - "Cut one hole and use the copper screw and nuts"
1. how and where and why to cut the hole?
2. copper fasteners for 400 mmsq cable termination? what diameter of fastener to use to get the desired contact pressure? what size of washers to use? and what surface of area to therefore maintain for proper contact?
3. co-efficient of linear expansion of copper being higher than steel can make joint loose more easily . . .
please explain the rationale / basis of your suggestion to enlighten us here . . .

It's amazing that there are places in the world where this sort of thing is carried out without suitable training and materials, and that a resort to a global anonymous Engineering forum is seen as an appropriate solution.