Whenever power is switched of pabx , any one of the line is work or not?

Question

Whenever power is switched of pabx , any one of the line is work or not?

Answer 1

If its a "key" system, then typically yes, the first line or two will automatically relay to the first extension or two.

BUT, if its a true pbx then the answer is almost always no.  PBX's don't typically have "normal" analog lines into them, some do, but most don't, and as a result, things like this aren't built in.

Most pbx's also typically only have proprietary extensions on them anyway, so they won't work without the pbx being online.

A properly designed and installed pbx will always have a backup power source that should work for several hours.

Answer 2

English please!

if you are asking if by turing off the power to a PABX once of the lines still works the answer is YES the first line  (or 2 lines if a 2 line PABX) are relay controlled so on power off they are hardwired to the 1 or 2 incoming lines.

its called fail-safe so in a power cut the incoming lines still function powered by the xchange but you cannot alter which phones do this!