any help from a genius one

Dear Guest,

More information is required. First you must specify the number of pair of cable and it is laid from which location to which location? that means weather from exchange MDF to DB or DB to telephone instrument? ( where to where?)Normally the telephone cables are laid from MDF to Junction boxes and from junction boxes , junction boxes to junction boxes or junction box to individual telephones. Main cable connections are made between two exchanges also. The possibility of AC voltage can be from an individual telephones and normally the individual protective fuse at MDF take care of such higher voltages damaging the exchange equipment by cutting of the particular pair. The source of the incoming voltage if any exists can be located from the respective pair. The other possibility is that you may be mistaking a ring current to be as AC source. Normally a voltage that is present in one pair do not affect the other pair. So make further check up and explain your problem specifically.

Here's a way. Short it out (beware BIG SPARKS - make sure all other CR4 readers are at a safe distance), and see who complains that their circuit protective device won't reset because of the short circuit.