I'm currently working on a job installing conduit for a cell tower on the top of a 12 story building in central New Jersey. For whatever the reason, some other contractor ordered most of the material on the job for us and I had a few questions about what we had to work with.

My main question is this, is it permissible to use threaded aluminim couplings to attach a piece of 2" aluminum conduit to a factory made 2" galvanized sweep?

Also, is this wiring method ok as far as considering this pipe run as the EGC when 2-types of metals are being used in the run?

This is the only referance i find, others may have more information, what did the project engineer have to say about it.
"The impedance of a circuit in an aluminum raceway or aluminum-sheathed cable will differ from the impedance of the same circuit in a steel raceway or steel-sheathed cable; therefore, separate raceways and cables must have the same physical characteristics. See 300.20 regarding induced currents in metal enclosures or raceways."

334.14 Dissimilar Metals
Where practicable, dissimilar metals in contact anywhere in the system shall be avoided to eliminate the possibilityof galvanic action. Aluminum fittings and enclosures shall be permitted to be used with steel RMC, and steel fittings and enclosures shall be permitted to be used with aluminum RMC where not subject to severe corrosive influences.

(BTW, some Noalox on the threads of the aluminum conduit will prevent the threads from galling or seizing and make installation much easier)

[This message has been edited by electure (edited 12-09-2005).]

Boy, this brings back memories of trying to pull new wires into buried aluminum conduit in south Fl.
The pipe was almost always nothing but white powder.
The problem got so bad that the south Florida building code didn't allow aluminum conduit within ten miles of the beach.

Thank you for the code referrence number. I was concerned that the 2" pipe was going to be used as the EGC but I later found out that a seperate 1" pipe had been run just for that reason. It's a neat job to be on considering I do mostly residential work and don't get to work with AL/ RMC all too much.

I started using AL RMC for my non-mast risers on resi gigs once I found out the PoCo & most AHJ's accepted it. It's quicker and cheaper than galvanized.

[This message has been edited by DougW (edited 12-11-2005).]