Where large systems are concerned, the main distribution frame (MDF) is placed away from the PABX equipment. Power surge protectors are placed in the DB. This can create a potential platform.

The MDF backframe is used as the platform which has a feedthrough power protector placed as close as possible to the data protectors. The earthing point is created close to the surge protectors and the electrical, building and other earths are connected to this one point. Should the PABX be placed far away, if will not be affected by transients, as long as the inputs and outputs are fed through the distribution frame.