One of the first lessons new electricians learn is that electricity will always look for the path of least resistance to get to ground.
The Occupational Safety and Health Administration (OSHA) has several regulations related to grounding, including 1926.404(f)(6). It says, “The path to ground from circuits, equipment, and enclosures shall be permanent and continuous.” Despite the jargon, the regulation serves a critical purpose in keeping us safe if a fault occurs.
In most cases, the path of least resistance for electricity will run through an electric appliance, whether it’s a motor, lightbulb, machine, or anything else requiring power to run. When this happens, the system is working, and all is right in the world.
When a fault in the system develops, the closed loop is broken, and the electrical current will look for the easiest way to get to ground. If the system isn’t permanent and continuous, it could spell disaster for people, nearby objects, and other materials.
Grounding and bonding provide a safety net for electricity, giving it a return path to follow back to ground if a fault occurs and ensuring people and equipment remain safe. For all their similarities, electrical bonding and grounding have several key differences; however, combining the two is a great defense against potential danger.
When thinking about grounding, always know what the end goal is supposed to be.
Grounding involves establishing a physical wiring path that gives electricity a way to get to earth if there is a fault in the system. It also includes connecting electrical equipment and appliances to the electrical source. Appliances and machines become safer because there is less risk of a shock hazard or electrical fire, and downtime is reduced.
When a fault or overcurrent occurs, grounding provides a safe path away from people and appliances, guiding electricity through a neutral wire to a drain-off point that completes the circuit. Examples of possible overcurrent situations may include:
Besides serving as a safety valve for errant electrical spikes, grounding helps reduce electromagnetic interference (EMI) from impacting sensitive low-voltage signals within electrical systems.
For something to be grounded, you typically need a system of grounding rods and clamps that allow electricity to flow safely to the ground.
Ground wires are easy to find in electrical systems because they are either bare copper wire or a copper conductor with green insulation and possibly a yellow stripe. Don’t worry – they all accomplish the same goal of safely moving electrical current in the case of a short circuit or ground fault.
When an electrical system works, ground systems don’t carry a current; all electricity in the closed system is handled by the hot and neutral wires. However, in the case of a surge, fault, or other overcurrent situation, electricity wants to travel the path of least resistance. When this happens, the ground system kicks in to send the current through the ground wire to a bus bar, then out to the source through the neutral line to complete the original circuit.
As the overcurrent races back to ground, it will travel through the low-impedance ground wire. The breaker will recognize the higher current level and trip, terminating the circuit and preventing electricity from flowing.
If grounding were Batman, then bonding would be Robin.
Bonding works in tandem with grounding by connecting metallic objects that may be exposed to electrical faults to the grounding neutral. During a fault, the current will trip the breakers for overcurrent devices as fast as possible. Bonding also supplies a route for static electricity and induced voltages to safely drain, reducing the possibility of a shock hazard.
When setting up bonding connections, conductors need to be sized to safely carry the largest load that might occur during a fault. Work with your local codes department to figure out how those conductors should be sized.
When you bond metals in an electrical system, you also increase the grounding system’s effectiveness. Commonly, you’ll find bonds between:
Bonding doesn’t offer protection and isn’t as effective without a grounding system. To ensure bonding works, it needs a grounding conductor to create a low-impedance path back to the electrical source to trip the breaker and cut power.
Bonding is meant to connect metal materials that aren’t supposed to carry current, so they all have the same electrical potential. What does this mean? It means that one material, piece of equipment, or metal pipe won’t have electricity building up in it. Because the metal parts have the same electrical potential, electricity can’t flow between them.
The National Electrical Code (NEC) does touch on electrical equipment bonding in Article 250 (A)(1.4), saying: “Normally non–current–carrying conductive materials enclosing electrical conductors or equipment, or forming part of such equipment, shall be connected together and to the electrical supply source in a manner that establishes an effective ground-fault current path.”
Later, in Article 250 (B)(2.2), the NEC further explains its grounding rules for electrical equipment. According to the regulations, non-current-carrying metal materials must be connected to the grounding equipment to allow the maximum fault current to make it to ground.
Bonding appliances and materials to a ground system are critical to safety.
By connecting bonded materials to a ground system, you minimize the effects of faults in the system and safely allow electricity to drain away from impacted appliances, machines, and other assets. It also prevents dangerous shocks from injuring or, worse yet, killing someone who accidentally encounters an affected machine.
Though bonding and grounding have unique differences, they help prevent accidents like fires and shocks. Knowing when and how to bond and ground will ensure every electrical system is safe.