Grounding existing 2 wire no ground

[oldertech]

Let's not forget that local codes can differ from the NEC. The most stringent requirement takes precedence.

[alexewing]

Ny breaker went off many times

[HVAC_Marc]

Im glad you asked too. If this is not acceptable a water pipe is?

A water pipe is NOT acceptable. Any electrical flow through the pipe, especially copper pipe, will cause electrolysis failures. Pinholes and leaks. When the ceiling or wall falls in or there's massive amounts of mold, it'll be on you.

Bonding is fine. That's designed to make all parts at equal electrical potential. Grounding gives a path back to the panel protection device. Grounding to a pipe it the biggest cause of pipe failures besides bad water.

Edit - I see this is an old post...