Sizing Earthing for Process Equipment

It depends. In USA the National Electric Code prvides tables to size ground (earth) conductors based either on service conductor size or overcurrent device setting ahead of equipment. It also depends on if AC or DC equipment, applied voltage, and static or lightning protection considerations.

As important as the ground or earth strap, the size and configuration of the actual earthing location is also a consideration. What is the capacity of the earth point, and what is the ohmic value? Are you connected to a single earth (ground) rod, ore are there multiple rods and connection points?

First identify the AC or DC voltage.

How many and what type of equipment. What is equipment layout?

What is the hazard you are trying to protect? worker safety from shock, or spark ignition hazard?

Provide this data, and there are many posters on this site who can help.

1MΩ is effectively a short circuit for static electricity.

Equipotential bonding for electrical safety, however, will be defined by a local code, most likely a factory-, company-, or client-wide specification. Mechanical strength is as important as conductor resistance.

Depending on operation and location of installation, quite often I find mechanical strength is more important.

("pumps won't work, because the vandals took the handles")