Why Circuit Breaker has neutral and no ground?
Its not about voltage it's about current. Old style circuit breakers toggle off when the current going through them is enough to trip a relay and work like a fuse.

"Earth leakage circuit breakers" also watch the neutral line. Theory being what ever go's UP  must come Down. That is the current  going out of the live wire does not match the current returning on the neutral wire, there must be a leak so ground somewhere... However it's a bit of a misnomer, the current could actually 'LEAK' back to the panel through some other neutral path too if the wiring is not correct.



The newest standard also detects electrical arcing in the system.