He has a point TBH.
Electricity can and does kill.
Zones and PA plus no rkp or bell linked or not will not be the cause.
If you have a test meter and you are confident enough kill all power.
Remove the leads from the transformer output to the panel.
Insulate them apart from each other and then turn on the mains.
If the fuse still trips it is a faulty transformer.
If not again power down and refit the transformer leads and remove
EVERYTHING FROM THE ZONES ECT, if it goes again faulty panel.
Remember only do this if you feel confident, otherwise get someone in.
PS hate the panel anyway, if it is faulty get something else.
AGAIN IF UNSURE GET SOMEONE, YOU KILL YOURSELF DONT COME RUNNING TO ME....................Not that you could anyway, but cannot reienforce the above enough.