Earthing of Plant Structures

Plenty. It all depends on which country it is in, Murphy.

The procedure is to connect the structures to the earth, with a ground wire.

Yes.

What dust is being collected?

You could end up with the problem of static discharge causing explosion and fire.

If the "dust" is anything other than inert then there are probably specific requirements for the design of the entire electrical system including the grounding. This is an area where considerable expertise is required for plant and personnel safety, hire experienced engineers for the job.

You haven't said which country!

Depending on the density of the dust in the air, even 'inert' particles can be a problem.

Sawmills, flour mills, grain silos, these all have had a tendency to explode because the dust (sawdust, ultra-fine flower, grain husk fragments) would reach a critical level of density in the air to allow for a 'fuel-air explosion,' each particle burns for just a fraction of a second, but it ignites its neighbors, which ignite their neighbors, and so on in an expanding front that is no different from black powder going off. Once that expanding front (and the heat expanded air within) reaches the limits of its enclosure, it's going to push out, and then you get your proper 'boom.'

The only non-combustible dust sources I can think of tend to be the ones you don't want to be around inhaling in the first place (silica dust, asbestos, etc).

Here is one of the regulation:-

| The purpose for grounding structures electrically is to provide maximum safety for persons in the vicinity of structures by limiting step and touch potentials. Also, electrical grounding limits the ground potential rise due to lightning strikes on structures by providing a low resistance path to remote earth. | No references to lightning protection are found in the AASHTO Specifications | except for Movable Highway Bridges. However, lightning protection design should | consider structure location, potential high-incident lightning areas and the | structure's risk to lightning damage to either the structure or structure electrical | systems or potential occupants. | Electrical grounding may be considered for all structures with pedestrian facilities | where chainlink fencing, steel girders, railing and lighting is detailed and new steel | structures which are more than 50 feet above water. | When required, an electrical grounding note is to be provided with construction | plans, taken from Figure 48.2. BRIDGE MANUAL ELECTRICAL GROUNDING OF STRUCTURES SECTION 48.2_________________________________________________________________________________________________________________________________ Date: May, 2004 Page 3 48.2 METHODElectrical grounding shall be accomplished by external grounding techniques for both existing and new structures at abutments. Additional electrical grounding | details should be provided on tied arches or trusses at their piers. | A bare copper stranded, single conductor, with an American wire gage size of 4/0 | shall be installed under the deck. This shall be attached to the end of a steel girder by exothermically welding and as well as to the abutment as deemed necessary by | UL listed cable fasteners spaced per manufacturer's recommendations. If the wire | is placed in concrete, it shall be protected with nonferrous conduit. Grounding shall be accomplished by attaching the copper wires to abutment piles by exothermically welding for new structures or to copperclad grounding electrodes | by exothermically welding for existing structures. The grounding electrodes shall be in compliance with the latest Underwriters Laboratory Specification 467 and American National Standards Institute Specification C-338. Reference may be | made to Figure 48.2 for electrical grounding details and specifications. | When protecting lightning system conductors in conduit, only nonferrous conduits | should be used. The magnetic properties of steel behave as a magnetic choke and | raise the impedance of the conductor to unacceptably high values. All electrical ground circuitry shall be field tested for electrical continuity. A ground resistance tester shall be used to verify ground resistance in accordance with the National Electrical Code. The proper exothermic mold and associated equipment shall be used for each connection. All materials used such as molds, weld material, accessories, and tools shall be supplied by one manufacturer to ensure compatibility. BRIDGE MANUAL ELECTRICAL GROUNDING OF STRUCTURES SECTION 48.2_________________________________________________________________________________________________________________________________ Date: May, 2004 Page 4 CL Abutment (Existing Structures) Attach 4/0 copper wire To copperclad electrode (5/8" Φ x 8' long) and steel girder with exothermic weld. Use two hole galvanized straps spaced a maximum of 10 feet apart to anchor exposed wire. All wiring outside abutment shall be below the ground line. CL of Continuous steel girders. CL of Pier Attach 4/0 copper wire to the end of a girder by exothermic weld. Attach 4/0 copper wire to a steel abutment pile by exothermic weld. Run copper wire through the abutment in nonferrous conduit and coil extra wire for later attachment to a steel girder. CL Abutment (New Structures)Plan of Steel Girder FIGURE 48.2

It is very improtant to know where you are operation on globe and what is the type of dust which is coollected in the plant???... to say something in answer. In anty case earthing steel structures will be needed but the process may differ with the info supplied.