Bus Bars of dissimilar metals

[berzerk]

I work for a switchboard manufacturer and have an AHJ questioning whether we can connect aluminum bus bar to copper bus bar. I'll need to provide to the AHJ documentation from a source such as U.L. 891 or the NEC. The only thing i found was in the NEC 110-14, but does not clarify the issue. I've seen this done many times before by different manufacturers so i know it has to be legal. This is a hard question to ask to get help on. So...can anybody help?

 

[Smart $]

Not sure how far this will get you.​

Excerpt from the Aluminum Electrical Conductor Handbook, Chapter 13 Bus Conductor Design and Applications, pages 13-45 to 13-46...

Aluminum·To-Copper Connection

Aluminum and copper are both ideally suited for use as
electrical conductors, not only because of their conductivity,
but also because both metals have an excellent inherent
resistance to atmospheric weathering. Because these two
metals are almost exclusively used as electrical conductors,
connections between the two metals have to be made frequently.
Such joints, when properly made with welldesigned
fittings of good quality. have given satisfactory
outdoor service for many years. It must be remembered,
however, that because of the electrochemical relation of
the two metals, aluminum is anodic to copper. As a consequence,
the joint in the presence of an electrolyte will be
susceptible to galvanic corrosion. The accumulation of
films or corrosion products on the contact surfaces may
adversely affect the electrical resistance of the joint.

The factors that influence the degree or the severity of
the galvanic action are numerous and complex. They are
covered in Chapter 2. For protection of instaUations in environments
that are known or expected to have severe
galvanic action, the joint should be thoroughly sealed with
a suitable grease-type compound to prevent the entrance of
moisture into the contact surfaces. Such compounds are
also used to minimize the formation of oxide films on the
contact surfaces. If possible, the copper side of the joint
should be placed on the bottom for outdoor applications
to prevent copper salts washing over the aluminum.

For ordinary applications (normal conductor
temperatures of 70°C), both outdoor and indoors, protective
grease-type compounds are effective and suitable for
controlling corrosion and maintaining low resistance in
direct aluminum-to-copper electric connections.

Links to the Handbook are near the bottom of this web page:
http://www.aluminum.org/resources/electrical-faqs-and-handbooks/electrical