Protecting People, Property, and Production with Proper Electrical Grounding
By: Dave Hernandez, Contributor
Ground fault protection is the most important safety mechanism to decrease shock hazards and prevent loss of life for workers or unqualified individuals who may inadvertently come into contact with equipment, frames, and enclosures.
Grounding plays a critical role in any electrical power system. The grounding system is a network that connects all components of an electrical power system to a line that is buried in the earth. The line carries excess fault current or unwanted electrical charge away from equipment, structures, and personnel through a path of least resistance, so that the current safely dissipates below ground. Proper grounding systems provide a reference point of zero volts in earth, and reduce damage, outages, accidents, injuries, and casualties.
Grounding systems provide many benefits for any type of facility using electrical power systems. They allow for a common reference point in the power system, which makes it easy to detect ground fault locations, identify short circuits, and measure data or unexpected incidents in the power system. Grounding systems form a defense against transient over-voltages caused by certain types of equipment, and help protect equipment via ground fault interrupters, lightning protection, and surge protection. Grounding systems improve safety for workers and lower the odds of high energy electrostatic hazards that can pose extreme dangers to people.
There are several types of grounding systems, each with a different function. The following takes a brief overview of the systems that are frequently deployed.
The Various Types of Grounding Systems
System grounding is the most common. It is used in most three-phase power systems. Every piece of equipment in the power system is run into a grounding grid, with grounding rods that are buried in earth at least 10 feet deep under the facility. Equipment grounding connects all non-current carrying metal parts to earth. This includes frames, enclosures, transformers, motors, conduit, junction boxes, cables, poles, and towers. Bonding is commonly used to merge electrically continuous materials. It utilizes infrastructure such as structural steel, plumbing, and other equipment to connect, lead, and feed unwanted electrical current into the grounding grid. These systems utilize green cables or solid, non-stranded uninsulated cables. All of the equipment is interconnected and electrically continuous to produce stability and proper grounding.
Neutral grounding systems are deployed for high energy equipment that generates electromagnetic fields. Parts such as transformers, generators, and motors create transient disturbances and electrostatic hazards. Static often builds up in insulating materials and can become a fire hazard or cause the air to become flammable. Neutral grounding systems provide the means to control and mitigate those disturbances by dissipating high energy charges or electrical faults that could damage gear or cause injuries to workers.
Lightning protection uses a conductor network to prevent incidents in towers, buildings, and other tall structures. Lightning strikes cause thermal effects that can spark fire hazards and harm or kill people. Conductor networks re-direct lightning strikes to ground, diverting harmful current away from buildings, equipment, and individuals.
Surge protection provides transient overvoltage protection caused by drives and motors.
Using drives to change motor speeds creates harmonic electrical instability and overvoltage conditions. If those overvoltages go undetected, they can cause equipment blowouts or arc flash events that cause injuries to people. Grounding re-stabilizes current levels when motors change speeds, helping to protect equipment and maintain production. Surge protection also mitigates the dangers of tall structures which produce transient overvoltages as part of regular electrical power system function.
Ground fault protection removes excess energy that accumulates in structural hardware and takes it to ground. Most large frames and enclosures are constructed of conductive material and can absorb voltages from energized parts. This creates a dangerous return path for fault current unless the current flow is diverted through a path of least resistance to ground. Damp, wet, or dusty environments require special attention to design and maintenance of ground fault protection. Water is highly conductive, and moisture or particle debris can accelerate the breakdown of equipment. Ground fault protection is the most important safety mechanism to decrease shock hazards and prevent loss of life for workers or unqualified individuals who may inadvertently come into contact with equipment, frames, and enclosures. This vital protection is the only way to remove a ground fault from the system. It prevents a person from becoming part of the circuit and suffering electrical shock.
More detailed information about any of the codes and standards related to electrical grounding can be found in National Electrical Code Article 250. It provides guidance on system grounding, equipment grounding and bonding, and conductive material bonding to create an effective ground fault current path to divert unwanted electrical hazards away from equipment that should not be energized. Tables 250.66, 250.102(C)(1), 250.122 provide helpful references for grounding, bonding, and sizing.
Consulting the NFPA 70E is the best way to ensure your system follows proper grounding procedures that will offer protections to your facility, equipment, and personnel. ESW
Dave Hernandez, PE, CEM, GBE, CESCP is a distinguished Professional Engineer licensed in 52 U.S. jurisdictions and serves as the Chief Executive Officer at Electrical Power & Safety Co (https://epsco.co), a world leader in electrical safety. He has held responsible charge of over 20,000 electrical projects, sits on various industry committees, and has authored several publications.