Can aluminum rigid coduit be used below ground for a 40 amp./240vac branch circuit to service air condition compressor outside a residential dwelling in NYC

How far underground could you possible have to go to a condenser?? How are the line sets run? Can't you mount a disconnect on the house and use sealtite following the line set?

To answer your question, yes, but care must be taken if concrete is involved. Any time AL conduit is put in a corrosive environment it must be protected from it.

Personally I would use PVC, I have seen problems with Aluminum conduit underground, However we are in a Salt environment.

Personally I would use PVC, I have seen problems with Aluminum conduit underground, However we are in a Salt environment.
Oh, I totally agree. NYC and LI are also quite salty environments.