What Is Equipotential Grounding? When it comes to equipotential grounding zones, or EPZ grounding, the definition is relatively simple. An equipotential zone is an area in which the electrical potential between any two points on a worker’s body is effectively identical.
Full Answer
What is an Equipotential Zone?
“Equipotential zone. Temporary protective grounds shall be placed at such locations and arranged in such a manner that the employer can demonstrate will prevent each employee from being exposed to hazardous differences in electric potential.”
What would happen if the gradient of a switchgear flattens out?
Again, though, be aware that if gradient levels flatten out, lethal voltages will be found at further distances.
What is the OSHA standard for switching 15 kV and 4160V?
It is highly recommended at all times if feasible. One clear requirement in this same OSHA standard is the creation of an equipotential work zone.
What is the resistance of an electrical worker?
OSHA assumes in 1910.269 that an electrical worker will represent a 500 ohm resistance. The 1 mA and 6 mA values above represent the current flow through an electrical worker who is unprotected from “involuntary muscle reaction due to shock”. These levels are all based upon proper design and installation of equipotential grounding prior to beginning work.
What happens if a 12.47 kV switch fails?
Historical data on switchgear maintenance, repairs, failures, etc. simply does not exist. Your company now owns the property. If this outdoor switch suffers a failure, a voltage gradient could form around the metal clad enclosure and surrounding area. The failure could be an internal insulator failure, a ground grid failure from lack of maintenance over time, or other potential failure mechanisms.
How far does voltage drop from a wooden pole?
Theoretically, if your site has uniform soil properties, about half of the source voltage drops within the first three feet of the defective wooden pole. This pattern continues every three feet beyond that first point, with the voltage dropping by one-half the previous value.
Why do we teach the shuffle method?
The shuffle method involves shuffling the feet without lifting them so that there is never more than 1/2 shoe length in front of the other shoe to ensure lethal voltages are not impressed across the worker’s feet.
How Is an Equipotential Zone Created?
The earliest methods of grounding work sites were little more than improvisations. In many cases, a small chain was attached to conductors that extended to the earth. However, in 1994, OSHA began enforcing rules about protecting workers from sudden re-energization caused by faults. This meant crews had to become more cognizant about how they were facilitating a safe working environment. For linemen working on poles, this means connecting clamps to the lines with safety wires leading to a grounding bar. At ground level, however, there is more real estate to cover.
Why is it important to have an equipotential zone?
These are all-in-one galvanized steel grates that can be placed to create zones where the electrical potential is equalized. Because they are extremely durable and can be locked for stability, they offer a more complete solution. When faults occur and there is an accidental exposure to electrical current, these grates direct it away from people and equipment.
What is the most effective grounding system?
When it comes to keeping them safe, an equipotential grounding system is typically the most effective method. Understanding what these are and how they work is critical for any contractor who has to operate around high-voltage infrastructure or equipment.
Why are equipotential grounding zones important?
Why Equipotential Grounding Zones Are Essential For Job Site Safety. It goes without saying that hanging electrical lines is dangerous work. Given the lethal amount of voltage in play, mitigating the risk for workers is the highest priority. In fact, 8.5% of all construction-related fatalities in 2018 were electrocution-related.
What is an EPZ zone?
An equipotential zone is an area in which the electrical potential between any two points on a worker’s body is effectively identical.
What is a Yak Mat grounding grate?
This includes substations, renewable energy sites and areas where lines are being installed. They have been performance-tested for a range of short-circuit capacity tests and current withstanding scenarios. Available in 4-foot-by-3-foot and 8-foot-by-14-foot sizes, they can be configured to cover ground areas of practically any size, no matter what type of terrain they feature.
What does grounding mean in electrical engineering?
Grounding means giving the current a way to return to the ground safely in the event of a fault. Because the voltage of the ground is effectively zero, there will always be a difference in potential and the current will flow into the earth as long as it has a pathway to take it there.
What Does Equipotential Bonding (EPB) Mean?
Equipotential bonding (EPB) is the process of electrically connecting metalwork and conductive parts, both exposed and extraneous, such that the voltage is the same throughout these various parts . EPB is used to reduce the risk of equipment damage and personal injury.
Why do we bond earthed materials?
Earthed materials are materials that are connected to the Earth’s conductive surface, often for the safety purpose of directing faulty current into the ground (tripping a fuse in the process) or dissipating potentially hazardous static discharges. Bonding multiple earthed items limits the magnitude of their voltages and prevents the existence of a dangerous potential difference (different voltages) between them. This eliminates the risk of a worker being shocked by a harmful electric charge flowing from one earthed item and through the worker, toward another earthed item of different voltage.
What is an equipotential work zone?
The IEEE’s standards for an equipotential work zone, as defined in IEEE Standard 524a, define such a work zone as one in which all equipment is interconnected by jumpers or grounding instruments, such that there will be an acceptable potential difference between all parts of the zone under a worst-case scenario of energization.
Why is it dangerous to work with two different objects at the same time?
This is because when a circuit is created between two points of varying potential energy/voltage, the energy will flow from the higher potential point to the lower potential point as fast as possible. This energy flow results in a current that will travel through the worker, which can be fatal if it is large enough. Equipotential bonding of earthed equipment ensures that the worker in an equipotential zone is protected because there is a nearly identical level of electrical potential between all points of the body.
What is OSHA 1048?
OSHA recognizes the methods prescribed by recognized standards organizations, such as the Institute of Electrical and Electronics Engineers’ IEEE Guide for Protective Grounding of Power Lines (IEEE Standard 1048), as complying with the requirements of OSHA’s standard.
How to draw equipotential lines?
The equipotential lines can be drawn by making them perpendicular to the electric field lines, if those are known. Note that the potential is greatest (most positive) near the positive charge and least (most negative) near the negative charge.
What is the most important case of parallel conducting plates?
One of the most important cases is that of the familiar parallel conducting plates shown in Figure 4. Between the plates, the equipotentials are evenly spaced and parallel. The same field could be maintained by placing conducting plates at the equipotential lines at the potentials shown.
How to represent electric potentials?
We can represent electric potentials (voltages) pictorially, just as we drew pictures to illustrate electric fields. Of course, the two are related. Consider Figure 1, which shows an isolated positive point charge and its electric field lines. Electric field lines radiate out from a positive charge and terminate on negative charges. While we use blue arrows to represent the magnitude and direction of the electric field, we use green lines to represent places where the electric potential is constant. These are called equipotential lines in two dimensions, or equipotential surfaces in three dimensions. The term equipotential is also used as a noun, referring to an equipotential line or surface. The potential for a point charge is the same anywhere on an imaginary sphere of radius surrounding the charge. This is true since the potential for a point charge is given by and, thus, has the same value at any point that is a given distance from the charge. An equipotential sphere is a circle in the two-dimensional view of Figure 1. Since the electric field lines point radially away from the charge, they are perpendicular to the equipotential lines.
What is equipotential surface?
An equipotential surface is a three-dimensional version of equipotential lines.
What is zero work?
Work is zero if force is perpendicular to motion. Force is in the same direction as , so that motion along an equipotential must be perpendicular to . More precisely, work is related to the electric field by
How do electric fields affect the heart?
An important application of electric fields and equipotential lines involves the heart. The heart relies on electrical signals to maintain its rhythm. The movement of electrical signals causes the chambers of the heart to contract and relax. When a person has a heart attack, the movement of these electrical signals may be disturbed. An artificial pacemaker and a defibrillator can be used to initiate the rhythm of electrical signals. The equipotential lines around the heart, the thoracic region, and the axis of the heart are useful ways of monitoring the structure and functions of the heart. An electrocardiogram (ECG) measures the small electric signals being generated during the activity of the heart. More about the relationship between electric fields and the heart is discussed in Chapter 19.7 Energy Stored in Capacitors.
Can a conductor replace a surface?
Because a conductor is an equipotential, it can replace any equipotential surface. For example, in Figure 1 a charged spherical conductor can replace the point charge, and the electric field and potential surfaces outside of it will be unchanged, confirming the contention that a spherical charge distribution is equivalent to a point charge at its center.
Equipotential Bonding Explained
Equipotential bonding is the best way to create “equal voltage.” A shock, however small, is the presence of voltage differences. As the voltage differences get larger, so does the danger. The amount of voltage that can be present on a pool deck or in a pool or spa could even cause serious harm. There can even be enough to cause death.
Is there a Code Requirement for Equipotential Bonding of Pools?
Yes, but the current 2017 version of the National Electric Code does NOT meet the minimum level of safety as determined by all labs and research agencies who have conducted testing or research, such as Electric Power Research Institute (EPRI), National Electrical Energy Testing Research and Applications Center (NEETRAC), ENERNEX, and IEEE.
What conductor is required for a double insulated water pump?
However, the Code does require the installation of an 8 AWG solid copper bonding conductor that is of sufficient length to make a bonding connection to a future replacement motor. This requirement is in the event that the replacement motor is not a double-insulated type motor. The bonding conductor is to be extended from the equipotential bonding grid to an accessible location near the motor. Where there is no connection between the bonding grid and the equipment grounding conductor for the premises, this bonding conductor is required to be connected to the equipment-grounding conductor of the pump motor circuit. This connection could be made at the motor termination compartment or in a suitable junction box or other enclosure [see NEC 680.26 (B) (6)].
What conductor is used for perimeter surface?
It should be clearly understood that if used, the 8 AWG or larger solid copper bonding conductor used for the “alternative means” for the perimeter surface equipotential bonding is not required to be extended, or attached to any remote panelboard, service equipment, or any grounding electrode. The sole purpose of this bonding conductor is to eliminate any voltage gradients or differences in voltage potential in and around the pool area. The purpose here is not to “ground” the pool structure. How much more grounded can you get than this huge concrete-and-metal structure buried in the earth containing thousands of pounds of water pushing it into contact with the earth even more?
What is required to bond pool water?
The pool water itself must also be bonded. An intentional bond of a minimum conductive surface area of 5800 mm 2 (9 in. 2) is required to be in direct contact with the pool water. This bonding can be accomplished with any of the conductive parts that are required to be bonded as described above. This could include such things as a metal pool ladder or railing where at least 9 square inches of the ladder is in contact with the water. A metal forming shell of a wet-niche luminaire can also satisfy this bonding requirement [see NEC 26 (C) and photo 1].
What is the purpose of bonding and grounding?
Grounding involves providing a low-impedance, ground-fault return path from the equipment required to be grounded back to the source of the electrical system, typically through the equipment grounding conductor routed with the branch-circuit conductors. This path facilitates the operation of the fuse or circuit breaker to allow it to remove the faulted condition. In short, bonding means “connected together,” while grounding means “connected to earth.” Grounding and bonding together provide the safety from shock hazards that is so important, particularly in an aquatic environment such as a swimming pool.
What is a bonding conductor?
The bonding connection between the various components of the equipotential bonding grid can be made with a series of solid copper conductor (s) or with rigid metal conduit of brass or other identified corrosion-resistant metal. If a conductor is used, it may be insulated, covered, or bare, but cannot be smaller than 8 AWG. This bonding conductor is not required to be extended or attached to remote panelboards, service equipment, or any grounding electrodes. This bonding conductor is, again, simply for bonding of metal components together, it is not intended for establishing a connection to earth or a ground-fault return path.
Why is bonding important in a pool?
Bonding requirements are an important and unique protective method employed to increase the safety of the users of bodies of water such as pools, spas, and hot tubs. Bonding connects the conductive elements of the pool structure, nearby metallic objects, and electrical equipment enclosures together. Bonding is required to eliminate voltage gradients (rises in voltage potential) in the pool area. When metallic parts are bonded together, they effectively eliminate differences of voltage potential that may exist between the individual conductive parts and thus reduce the shock hazard. If these metallic conductive parts are not bonded together, this leaves these conductive parts having the potential of being at different voltage potentials. In a case like this, the human body can serve as a “conductor” between two conductive parts at different voltage potentials if contact is made with these conductive parts. If a conductive path is provided between two conductive parts at different voltage potentials, this current is going to naturally equal itself out between these conductive parts. An electrical shock occurs when the human body is used as the “conductor” between these conductive parts. If these conductive parts are mechanically, electrically, and intentionally bonded (married) together, there is typically no shock hazard present as these conductive parts are always at the same voltage potential.
What is the NEC 680.26?
The Code describes the basic bonding requirements and provides a list of items required to be bonded together. These bonding requirements can be found at NEC 680.26 (B). Included are the following metal parts that must be bonded together: