Testing and Inspection of Bonding/Grounding systems

The proper installation of bonding and grounding devices is important in the protection of personnel and equipment. At the time of installation a resistance test is needed to confirm electrical continuity to ground. In addition, an effective inspection and maintenance program is needed to ensure continuity adequacy of the system.
           In evaluating maintenance requirements, the bonding and grounding system can be divided into three categories:

• The point-type clamps equipped with flexible leads used for temporary bonding of portable containers to the building grounding system.
• The fixed grounding cables and bus bars used to connect the flexible leads and fixed equipment to ground.
• The earthing electrode itself

              The flexible leads are subject to mechanical damage and wear, as well as corrosion and general deterioration. For this reason they should be inspected frequently. This inspection should evaluate cleanliness and sharpness of the clamp points, stiffness of the clamp springs, evidence of broken strands in the cables, and solidity of cable attachments. A more thorough inspection should be made regularly, using an intrinsically-safe ohmmeter to test ohmic resistance and continuity.
           One lead of the ohmmeter is connected to a clean spot on the container, the other lead is connected to the paint grounding bus, metallic piping, or other fixed equipment. The measured resistance should be less than 25 ohms, and will usually be about one ohm.
               The fixed leads and the bus bars are not usually as subject to injury or wear as the temporary connectors. These should be checked with an ohmmeter on an annual basis. One lead of the ohmmeter should be connected to the fixed lead or bus bar, the other lead should be connected to the plant earthing electrode or to the structural steel of the building. The measured resistance should be less than one ohm.
           Conductive hoses should be checked regularly, and after repair or replacement, for electrical continuity and resistance. The conductive segments may break and may not be repaired properly, thus rendering the hoses nonconductive or with an abnormally high resistance. Nonconductive hoses having an internal spiral conductor should be installed so that the spiral conductor makes contact with adjacent metallic fittings.

Earthing Electrodes

            The final component of the bonding/grounding system is the “earthing electrode” which passes static charges into the soil. This may be a device installed solely for grounding purposes, such as a driven rod (copper clad) or buried plate, or it may be an underground metal water pipe. If the building has a steel structure frame that is grounded for lighting protection or is otherwise effectively grounded, this grounding is adequate for static grounding; no separate static earthing electrode is needed.
             Underground piping equipped with cathodic protection is not a suit­able ground. Underground piping made of cement-asbestos or plastic would not be satisfactory as a ground. It is also possible for metal piping to have sections of plastic or cement-asbestos which would make it unsatisfactory. Water meters should have jumper cables permanently installed around them to provide a continuous electrical path. When underground piping is utilized as a ground, any disconnections for alterations or repair may make the grounding system ineffective.
             Sprinkler piping and electrical conduit should be avoided because of the increased resistance to ground caused by joints and connectors. A break in continuity can also result when piping and conduit are removed for repair or alterations.

Grounding Verification Control System

Properly labeled “The Invisible Enemy”, static electricity cannot be seen but poses extreme risks if not properly attended to. Yet we rely on a visual means to confirm that a ground clamp and lead are in place for proper grounding or bonding, with periodic confirmation via resistance meters. Newer “electronic verification systems” now take the guesswork out of proper grounding techniques. These verification systems offer a continuous means of visual/electronic confirmation of ground to a high-integrity ground point (ground bus). Through “interlock” functions they can control pumps, valves, motors, etc. or interface with a PLC or DCS control system to ensure that nothing happens until a good ground is achieved. They may also initiate sound alarms if required. Further information on the various systems can be found in this booklet.

Drawings of Typical Arrangements for Grounding

The drawings shown in this book are approved concepts. If  there is any question regarding local fire codes, check with your Fire Marshall.