By Samuel Rokowski, Contributor
You can’t talk about electrical safety in the workplace without involving some of the discussion around bonding and grounding. In 2016, OSHA determined what is called “The Fatal Four”, one of which being electrocution on job sites. In that year, electrocution hazards led to 82 deaths, which is 8.3% of the 991 fatalities caused in the construction industry. The biggest problem in the industry is a misunderstanding and use of the requirements for grounding in bonding in the National Electrical Code.
What is the effective ground fault current path, and why is it so important? Because this path is a low impedance electrically conductive path that is designed to carry current during ground fault conditions and is designed to operate the overcurrent protection device or ground fault detectors (See NEC Article 100). To put it simply, without this low-impedance path during ground-fault conditions, normally non-current carrying metal and conductive materials are energized and can lead to shock or electrocution.
In this article I would like to focus attention on the requirements of bonding and grounding equipment and maintaining the effective ground fault current path to protect equipment and the safety of personnel in accordance with the 2020 National Electrical Code. My attention will focus on grounded systems only.
The Effective Ground Fault Current Path
It would be simple to understand this path if the path was singular, but it is not. The effective ground fault current path is a system of conductors and electrically conductive equipment that are connected to each other that creates this low impedance path. This path consists of any combination of conductors, equipment grounding, metallic raceways, metallic cable sheaths, electrical equipment, and other normally non-conductive metal material including building steel, metal piping systems, concrete encased rebar, shields of communications circuits, and the Earth. Understanding and maintaining this system is the difference between eliminating electrocution hazards or introducing them on electrical equipment.
General Requirements for Bonding and Grounding
So, what is the difference? Bonding is to mechanically connect metal equipment, raceways, and conductors to establish electrical continuity. Grounding is connecting conductors, metal equipment, and raceways to a conductive body that extends to the Earth. Both are key components of the effective ground-fault current path.
Section 250.4 of the 2020 Edition of the National Electrical Code states the general requirements for bonding and grounding. Grounded systems are required to have grounding in accordance with section 250.4(A)(1). All electrical systems that are grounded shall be connected to Earth in such a manner that the system will limit voltage imposed by ground faults, unintentional contact, lighting, and higher voltage systems. Grounding and bonding both act together to limit voltage that may be imposed. All normally non-current-carrying conductive components that enclose electrical conductors and equipment shall be connected to Earth. At the same time normally non-current conductive materials shall be mechanically connected together and to the supply source in order to establish an effective ground-fault current path.
Another often misunderstood issue with improper grounding and bonding is objectionable current. Objectionable current happens when a parallel path is created by an improper neutral to case bond and allows current to flow on normally non-current-carrying metal without the proper return to the power supply that would trip the overcurrent protection or ground fault protective device. This current on normally non-conductive materials can lead to electrical shock or electrocution.
Section 250.6 of the National Electrical Code addresses objectionable current and advises on how to avoid and eliminate any that exists. It states that the grounding of electrical equipment, circuit conductors, surge arrestors and protective devices, and normally non-current carrying metal shall be arranged in a manner that prevents objectionable current. In section 250.6(B) the code provides alterations that can be used to stop objectionable current, they include:
- To discontinue or disconnect one or more of the grounding connections to remove the objectionable current, but not all the connections.
- Change the grounding connection locations.
- To interrupt the conductor or continuity that is creating the objectionable current.
- Utilize another suitable approved means
It is important to note that temporary currents that are considered ground-fault, or abnormal conditions cannot be classified as objectionable currents. There are no alterations to ground fault or abnormal conditions, the circuit needs to be de-energized immediately.
Permitted Methods of Connection when Grounding and Bonding Equipment
The code specifies permitted methods for connecting the equipment grounding conductors, grounding electrodes, and bonding jumpers in section 250.8(A). Equipment grounding conductors, bonding jumpers, and grounding electrodes shall be connected by one of the following means:
- Listed pressure connectors
- Terminal bars
- Pressure connectors listed as grounding and bonding equipment
- By exothermic welding
- Machine screw-type fasteners that engage not less than two threads or are secured with a nut
- Machine screw-type fasteners that engage not less than two threads or are secured with a nut
- Connections that are part of a listed assembly
- Other listed and approved means
Keep in mind in accordance with section 250.8(B), grounding and bonding connections shall not rely on soldering connections. These connections are fragile and may break with vibration and movement.
Anytime that there are exposed ground clamps or other fittings, those fittings shall be protected by enclosing them in metal enclosures, wood, or anything equivalent.
Section 250.12 identifies the surfaces that grounding and bonding connections will be attached to shall have a clean surface and be free of nonconductive coatings such as paint, lacquer, and enamel. Don’t confuse this with the conductive paint that electrical manufacturers use to coat electrical equipment that is conductive, it’s regarding foreign materials.
Equipment Grounding and Equipment Grounding Conductors
The code identifies in section 250.109 that metal enclosures are permitted to connect equipment grounding conductors, bonding jumpers, or both to become a part of the effective ground-fault-current path. Any metal cover or fitting attached to the metal enclosures are considered connected to the equipment grounding conductors, bonding jumpers, or both. This is important to understand that if a fault happens on the cover, the low-impedance path will still clear the fault.
Equipment fastened in place or connected by permanent wiring methods that may become energized shall be connected by an equipment grounding conductor where within 8ft vertically or 5ft horizontally of ground or grounded metal objects subject to contact by people, when located in damp or wet locations and not isolated, in hazardous locations, where the wiring method provides the equipment grounding conductor, and for equipment that operates at over 150 volts to ground in accordance with section 250.110.
Equipment connected by cord and plug shall be connected to the equipment grounding conductor in hazardous locations, where operated at 150 volts to ground, in residential occupancies and other than residential occupancies that are connected to refrigerators, freezers, air conditioners, laundry appliances, non-portable kitchen appliances, portable luminaries, motor-operated tools, among other loads in accordance with section 250.114. Note, there are some exceptions to the identified cord and plug connected loads.
Equipment Grounding Conductor Types and Identification
Equipment grounding conductors don’t always have to be the conductor type. The code recognizes many different types including some more common ones, like the conductor type, solid metal conduits, listed flexible metal conduits that meet specific conditions, Armor type AC cable, metal-sheathed cable, MC cable that meets specific conditions, cable-trays, cable bus, and other listed electrically continuous metal raceways and gutters in accordance with section 250.118. These electrical conductors, raceways, cables, trays, and other listed means act as the equipment grounding conductor and are a part of the effective ground-fault current path.
In section 250.119, the code outlines that acceptable identification for equipment grounding conductors. Equipment grounding conductors shall be insulated, covered, or bare. The covered or insulated type equipment grounding conductors shall have a continuous green outer finish, or green with one or more yellow stripes. Conductors meeting the criteria specified shall not be used as ungrounded or grounded circuit conductors. Conductors that are 4 AWG or larger are permitted to be permanently identified as an equipment grounding conductor at each end at the time of insulation, see section 250.119(A).
The majority of electrical professionals that I meet fail to completely understand the requirements of bonding and grounding in the National Electrical Code. Article 250 is long, often confusing, and takes someone experienced to completely understand it. Do your part in the industry and the workplace to keep yourself, and those around you safe from shock and electrocution by understanding the requirements and maintaining the effective ground-fault current path. It’s definitely not an easy task to do, it will take time, patience, and hard work; but that is no comparison to the risks you take when you don’t understand the requirements. ESW
Samuel Rokowski is a licensed electrical plans examiner, electrical inspector, a licensed electrical contractor in multiple states, and a Principal on NFPA 70 & 72.