It is common for clients to disregard Grounding as an unimportant part of an Electrical design and adhere to the attitude “it’s just Grounding”. We are discussing Grounding as part of National Code Month because we feel it is categorically the most important part of a building design, an entire industrial process, or even the smallest of electrical systems. Grounding eliminates the dangerous voltage that exposed parts contain which could cause an electric shock if a grounded person touches them. It limits the build-up of static electricity when handling flammable products or electrostatic-sensitive devices protecting equipment.
A correctly designed electrical grounding system can protect the facilities’ electrical system from potentially dangerous conditions such as a lightning strike, voltage surges, or static build up where a system can be overloaded and cause a building fire, extensive damage to equipment, or even the worst case, a fatality.
Article 250, titled “Grounding and Bonding” of the National Electrical Code (NEC) is broken down into Ten Parts which are referenced throughout the entire NEC Articles:
- Part I. General
- Part II. Grounding Systems
- Part III. Grounding Electrode System and Grounding Electrode Conductor
- Part IV. Enclosure, Raceway and Service Cable Connections
- Part V. Bonding
- Part VI. Equipment Grounding and Equipment Grounding Conductors
- Part VII. Methods of Equipment Grounding
- Part VIII. Direct-Current Systems
- Part IX. Instruments, Meters and Relays
- Part X. Grounding of Systems and Circuits of over 1000 Volts
The NEC breaks down grounding systems into two categories; Below Grade Grounding and Above Grade Grounding. For Below Grade Grounding, electrodes such as ground rods or grounding mats may be used for items such as: buildings, stacks, or outside equipment pads. Above Grade Grounding covers items like: equipment ground conductors, bonding, system bonding, and grounding electrode conductors.
A few tables that are critical to use while designing a Grounding system are Table 250.66 Grounding Electrode Conductor for Alternating-Current Systems, Table 250.102(C)(1) Grounding Conductor, Main Bonding Jumper, System Bonding Jumper, and Supply-Side Bonding Jumper and Table 250.122 Minimum Size Equipment Grounding Conductors for Grounding Raceway and Equipment. Also Part III, Grounding Electrode System contains valuable information.
Here is an example of a Grounding project that Pearl Engineering was awarded: Our client discovered that their existing ground network was showing signs of deterioration especially in the areas of the aluminum earth ground conductors. Because these conductors no longer provided a continuous path to their buildings and equipment, we were hired to design an electrical grounding system which improved the existing ground grid in terms of safety and reliability by safely carrying current into the earth without exceeding any equipment limits. After extensive investigation, we determined that a new set of 500MCM ground conductors below grade were needed that would ensure sound ground connections between buildings and equipment. New ground conductors were installed in 36” below grade trenches and copper clad ground rods were installed along the new ground conductor route where connections were made to the new ground conductors. After the new cables were installed the ground grid underwent Point to Point Resistance and Fall of Potential testing. The resistance from these tests were used to create a model of the ground grid to determine the grid Step and Touch Potentials. The result of the Ground Grid Resistance Test compared closely to the calculated computer model value and were deemed similar enough to provide confidence in the accuracy of electrical Grounding System.
Every grounding project is unique, but the end result should always be a grounding system that provides a safe path for current to release through the electrical circuit to ensure safety to people, building structures and equipment. Pearl Engineering’s electrical team would be happy to support you on your next project and as we have learned in this article, even the smallest electrical projects require grounding.