I was wiring an A/C unit replacement today at a townhouse. The old unit was wired with 6/2 AL and was on a D.P. 60amp circuit breaker. Company policy in this particular situation is to NOT USE the old wiring and install a new circuit. I simply "boxed-off" the old 6/2 AL and disconnected it at the panel. Is there a code in the NEC that disallows doing this?

Sounds like good practice.

Where the code addresses abandoned cable, it generally either wants it either treades as hot- wire nuts, junction box, etc, or it wants it removed.

The "detail" is that the NEC does not address abandoned power wiring. Abandoned phone lines, yes- but not the stuff that can zap you.

Thank you Reno. Now I know for sure that my boss was just testing my knowledge of the code. I knew I had done nothing wrong but I was still like "humina-humina" when he was telling me this.