18 May 12 20:50
I don't know much about the physical construction of conveyors, but consider the following:
USE OF EQUIPOTENTIAL BONDING:
I assume the conveyor is steel. What is the problem with using equipotential bonds to earth your structure? e.g. use copper braids or strand Cu with lugs where there is no good bolted connection between sections. The perhaps just bring back two (N-1) bonds from the closest conveyor section to the main earth bar at the switchroom.
EARTHING VIA GENERAL MASS OF THE GROUND:
If the supports are steel with no insulating sections and you are using concrete foundations with steel reinforcement, then the structure is already earthed. Simulate a the foundation in a popular earthing software package GDEGs, Ground MAT, etc. to get your earth resistance at each structure. these are all in parallel. Adding the earth electrodes may be a waste of time.
If it is not already constructed, maybe welding a galvanised tag to the foundation reinforcement which penetrates the concrete and has a hole for a further connection to the steelwork/conveyor would guarantee a more solid connection if the steelwork is painted instead of galvanised.
If you are worried about the impedance of the steelwork, you can work out the resistance of the conveyor if you know the cross sectional area and length. Then just put this resistance in your short circuit and see if the current will be large enough to trip out your breaker if there is a line to ground fault at the furthest end of the cable.