Understanding Static Electricity Grounding and Bonding for Safety and Compliance

Understanding Static Electricity Grounding and Bonding: Essential Safety Practices for Industrial and Power Plant Environments

By Safety Electric Editorial Team

Static electricity is a common yet often underestimated hazard in many industrial settings, including power plants, chemical processing facilities, and manufacturing operations. Accumulated static charges can lead to dangerous sparks, fires, or explosions, especially when flammable or combustible materials are present. Effective grounding and bonding practices are critical control measures to mitigate these risks by safely dissipating static charges and preventing hazardous potential differences.

In this article, we explore the fundamentals of static electricity grounding and bonding, their practical relevance in industrial and power plant environments, common mistakes to avoid, and implementation advice that ensures compliance and safety. Whether you are a safety officer, engineer, or maintenance professional, this comprehensive guide will help you understand and apply these essential electrical safety principles.

What Is Static Electricity and Why Is It a Concern?

Static electricity results from the imbalance of electric charges on the surface of materials. It commonly occurs through friction, separation of materials, or movement of liquids and powders within pipes and containers. The accumulated charge can discharge suddenly as a spark, which, in hazardous environments, can ignite flammable vapors, dust clouds, or gases.

Industries such as petrochemical refining, pharmaceuticals, grain handling, and power generation are particularly vulnerable to static hazards. For example, in power plants, static buildup on fuel handling equipment or insulating materials can pose ignition risks. Therefore, controlling static electricity is a critical part of electrical safety and fire prevention programs.

Grounding and Bonding: Definitions and Differences

Before diving into application details, it’s important to clarify the terms grounding and bonding, which are often used interchangeably but have distinct meanings:

• Grounding refers to the connection of electrical equipment or conductive objects to the earth (ground) to provide a low-resistance path for electrical currents, including static discharge, to safely dissipate.
• Bonding means electrically connecting two or more conductive objects together to equalize their electrical potential and prevent voltage differences that could cause sparks or shocks.

Both grounding and bonding work together to prevent dangerous static discharges by ensuring that all conductive parts remain at the same electrical potential and that excess charge can flow harmlessly to earth.

Practical Relevance of Grounding and Bonding in Industrial and Power Plant Settings

Static electricity grounding and bonding are indispensable in environments where flammable or explosive atmospheres exist or where sensitive electronic equipment is used. Here are practical examples of their importance:

• Fuel and Chemical Transfer: During loading/unloading of flammable liquids, static buildup can occur due to liquid flow through pipes and hoses. Grounding the containers and bonding the equipment prevents spark generation.
• Powder Handling and Dust Control: Conveyors, mixers, and storage vessels handling combustible dust require bonding to avoid potential differences that can ignite dust clouds.
• Electrical Equipment and Structures: In power plants, grounding systems ensure that static charges on metallic structures, cable trays, and machinery are safely discharged, reducing shock risks and equipment damage.
• Personnel Safety: Proper bonding of conductive floors, platforms, and tools minimizes the risk of static shock to workers, which can be both a safety and comfort issue.

Key Principles for Effective Static Electricity Grounding and Bonding

1. Ensure Continuous Conductive Paths: All conductive components that may accumulate static charges must be bonded together with low-resistance connections to maintain equal potential.
2. Use Appropriate Grounding Electrodes: Ground rods, plates, or mats must be installed to provide a reliable earth connection with minimal resistance to dissipate static charges quickly.
3. Regular Inspection and Testing: Grounding and bonding connections can degrade over time due to corrosion, mechanical damage, or looseness. Scheduled maintenance and resistance testing are essential.
4. Consider Material and Environmental Factors: Use corrosion-resistant materials and design grounding systems to accommodate site-specific soil resistivity, moisture, and temperature conditions.
5. Integrate with Overall Electrical Safety Systems: Grounding and bonding for static control should complement the facility’s electrical grounding systems to ensure comprehensive protection.

Common Mistakes in Static Electricity Grounding and Bonding

Despite its importance, improper grounding and bonding practices are frequently observed in industrial environments. Common errors include:

• Incomplete Bonding: Leaving conductive parts isolated or improperly connected creates voltage differences and potential spark points.
• Use of High-Resistance Materials or Connectors: Using paint, rust, or non-metallic materials at bonding points increases resistance and impedes charge dissipation.
• Neglecting Personnel Bonding: Overlooking the grounding of worker platforms or tools can lead to static shocks and unsafe conditions.
• Ignoring Regular Testing: Assuming grounding and bonding systems are permanent and fail-safe without periodic verification.
• Mixing Grounding Systems Improperly: Combining static grounding with electrical fault grounding without proper design can cause interference or unsafe conditions.

Implementation Advice for Industrial and Power Plant Environments

Implementing a robust static electricity grounding and bonding program involves several practical steps:

1. Conduct a Static Hazard Assessment: Identify processes, equipment, and materials prone to static buildup. Evaluate ignition risks and required control levels.
2. Design Grounding and Bonding Systems: Develop plans based on recognized standards and best practices, ensuring all conductive parts are interconnected and grounded.
3. Select Quality Components: Use high-conductivity straps, clamps, cables, and grounding electrodes suitable for the environment and load conditions.
4. Train Personnel: Educate workers and maintenance teams on the importance of grounding and bonding, safe handling practices, and how to recognize static hazards.
5. Establish Inspection and Maintenance Protocols: Schedule regular visual inspections and electrical resistance measurements to verify system integrity and functionality.
6. Coordinate with Electrical and Fire Safety Teams: Ensure static control measures integrate with overall facility safety management systems.

Conclusion

Static electricity grounding and bonding are fundamental safety measures that prevent ignition hazards and protect personnel and equipment in industrial and power plant environments. Understanding the science behind static charge accumulation and discharge, combined with diligent implementation of grounding and bonding practices, significantly reduces fire and explosion risks.

By avoiding common pitfalls and following a structured approach to design, installation, and maintenance, facilities can maintain safe operations and comply with electrical safety best practices. As power demands and industrial processes evolve, particularly with the increasing electrification and use of sensitive electronic systems, grounding and bonding will remain a cornerstone of effective electrical safety management.

Key Takeaways

• Static electricity can cause dangerous sparks leading to fires or explosions in industrial settings.
• Grounding provides a path to earth to safely dissipate static charges; bonding equalizes electrical potential between conductive parts.
• Proper grounding and bonding are critical in fuel handling, dust management, electrical equipment, and personnel safety.
• Common mistakes include incomplete bonding, high-resistance connections, and lack of regular testing.
• Implementation requires hazard assessment, quality components, training, and maintenance protocols.
• Integrating static control with overall electrical and fire safety systems enhances facility-wide protection.

References and Further Reading

• Access to real-time electricity data should be a basic consumer right | Utility Dive
• Net electricity generation jumped 4.5% in March as the West baked under record heat | Utility Dive
• Too Much Too Fast? Analyst Warns AI Data Center Scramble Threatens Power Projects, Electricity Customers | TD World

Grounding Fault Protection in Electrical Systems for Enhanced Safety and Reliability

Understanding Grounding Fault Protection in Electrical Systems

By Safety Electric Editorial Team

Grounding fault protection is a critical component in maintaining the safety and reliability of electrical systems, especially in demanding industrial environments like manufacturing plants and power generation facilities. Ground faults, which occur when unintended electrical paths to ground develop, can lead to equipment damage, fire hazards, and even fatal electrical shocks. This article explores the principles of grounding fault protection, common challenges in implementation, and practical controls to enhance safety and system integrity.

What Is Grounding Fault Protection?

Grounding fault protection refers to the detection and interruption of unintended electrical currents flowing directly to ground. These faults can arise from insulation failures, damaged cables, or moisture ingress, creating hazardous conditions. Effective grounding fault protection systems identify these faults quickly and isolate the affected circuit to prevent escalation.

Why Ground Faults Are Dangerous

• Shock risk: A ground fault can energize conductive surfaces, posing a serious electrocution hazard to personnel.
• Fire hazard: Fault currents can generate excessive heat, igniting combustible materials.
• Equipment damage: Prolonged faults can degrade insulation and damage sensitive equipment.
• Operational disruption: Undetected faults can cause unexpected outages and costly downtime.

How Grounding Fault Protection Works

Ground fault protection systems typically monitor current flow in the electrical system’s conductors. When current leaks to ground, it creates an imbalance between the supply and return currents. Protective devices detect this imbalance and trip the circuit breaker or activate an alarm. Common devices include Ground Fault Circuit Interrupters (GFCIs) for low-voltage applications and Ground Fault Relays or Residual Current Devices (RCDs) for industrial power systems.

Key Components of Ground Fault Protection

1. Grounding system: Provides a reference point and a low-resistance path to safely divert fault currents.
2. Fault detection device: Senses current imbalances or voltage changes indicating a ground fault.
3. Protective relay or interrupter: Acts on detection signals to open the circuit and isolate the fault.
4. System grounding conductor: Connects equipment frames and neutral points to earth ground to stabilize voltage and facilitate fault clearing.

Industrial and Power Plant Relevance

In industrial plants and power generation facilities, grounding fault protection is vital for both safety and system reliability. These environments often operate at higher voltages and currents, increasing the potential severity of faults. For example, power plants integrating renewable energy sources like wind turbines face unique protection challenges. As inverter-based resources (IBRs) behave differently during faults—often limiting fault current magnitude—traditional protection schemes may require adaptation to maintain effective grounding fault detection and response (source [1]).

Furthermore, industrial settings typically employ complex electrical distribution networks with sensitive control systems. Ensuring grounding fault protection is properly coordinated with other protective devices is essential to prevent nuisance trips and maintain continuous operation.

Practical Controls for Effective Grounding Fault Protection

• Regular system grounding audits: Verify that grounding conductors, electrodes, and bonding connections meet electrical codes and are free of corrosion or damage.
• Use of appropriate protective devices: Select GFCIs, RCDs, or ground fault relays rated for the specific voltage and application.
• Setting sensitivity thresholds properly: Avoid too low thresholds that cause nuisance trips or too high thresholds that delay fault clearing.
• Implement communication-assisted protection schemes: Especially in modern grids with inverter-based generation, integrating phase and ground distance elements improves fault detection reliability (source [1]).
• Routine testing and maintenance: Perform ground fault relay testing and insulation resistance checks to ensure protection devices respond promptly.
• Training and awareness: Educate maintenance and operations personnel on grounding fault hazards and protection device functions.

Common Mistakes in Grounding Fault Protection

1. Neglecting grounding system integrity: Poorly maintained or inadequate grounding paths compromise protection effectiveness.
2. Inappropriate device selection: Using devices not suited for the system voltage or fault current characteristics can result in missed faults or false trips.
3. Ignoring inverter-based generation impact: Failing to adapt protection settings for renewable integration leads to protection blind spots.
4. Overlooking coordination between protective devices: Improper coordination can cause cascading trips or failure to isolate faults promptly.
5. Insufficient personnel training: Lack of understanding about grounding faults and protection devices increases risk of unsafe work practices.

Implementation Advice for Industrial Facilities

Implementing grounding fault protection effectively requires a systematic approach:

1. Conduct a comprehensive electrical system study: Identify all potential fault paths and evaluate existing protection schemes.
2. Engage qualified electrical engineers: Utilize their expertise to select and configure protection devices based on system characteristics and operational requirements.
3. Leverage transient and fault modeling: Simulate fault scenarios, especially when integrating new technologies like wind or solar power, to optimize settings (source [1]).
4. Establish maintenance and testing protocols: Schedule regular inspections, relay testing, and grounding system verification to maintain protection readiness.
5. Implement training programs: Ensure all staff understand electrical hazards, grounding fault risks, and safe work practices as emphasized by electrical safety organizations (source [2]).
6. Document protection settings and procedures: Maintain clear records to support troubleshooting, audits, and continuous improvement.

Key Takeaways

• Grounding fault protection is essential to prevent electrical shock, fire, and equipment damage in industrial and power systems.
• Ground faults create current imbalances that protective devices detect to isolate faults rapidly.
• Modern power systems integrating inverter-based renewable energy require adapted protection strategies.
• Proper grounding system maintenance, device selection, and coordination are critical for effective protection.
• Regular testing, staff training, and system studies enhance safety and operational reliability.

References and Further Reading

• Adapt Line Protection For Wind Integration | TD World
• Electrical Safety - Electrical Safety Foundation International
• Your Home Electrical System - Electrical Safety Foundation International
• How Do You Know? Electrical Safety Awareness Videos - Electrical Safety Foundation International

TEMPORARY PERSONAL PROTECTIVE GROUNDING BASICS

What is temporary personal protective grounding?

Sometimes, additional measures are desirable to provide an extra margin of safety assurance. Temporary personal protective grounds are used when working on de-energized electrical conductors to minimize the possibility of accidental re-energization from unexpected sources. Sometimes these are called safety grounds or equipotential grounding.

Induced voltages, capacitive recharging, and accidental contact with other circuits can occur. Depending on the electrical energy available, these occurrences could cause injury or death.

More often, however, they only cause reßexive actions. For example, although most induced voltages will not normally cause serious injury themselves, they could cause a person to jump backward suddenly, possibly tripping against something or falling to the floor.

Temporary protective grounding devices should be applied where such conditions might occur. Temporary personal protective grounds should be applied at possible points of re-energization. They can also be applied in such a way as to establish a zone of equipotential around a person.

When these grounds are used, they shall be connected tightly, since they establish a deliberate fault point in the circuit. If current does somehow get onto the circuit, the grounds shall stay connected securely until a protective device clears the circuit.

It is difficult to set firm criteria for when temporary personal protective grounds are needed. Blanket requirements are usually established. Many times, it is a decision made in the field by the person performing the work.

When there is uncertainty about exposure, it is wise to add this extra protection. Many industrial facilities and utilities require temporary personal protective grounding for all aerial power line work and for all work on power systems over 600 V because of the increased exposure these systems often have due to their length and location.

Temporary personal protective grounding can also be used as the additional safety measure required when hazardous electrical energy control must be performed using a tag only. Temporary personal protective grounding devices should meet the specifications in ASTM F855-96 and should be sized for the maximum available current of any possible event.

Temporary personal protective grounds should only be installed after all other conditions of an electrically safe work condition have been established. Because the unexpected can happen at any time, however, the installation and removal of temporary grounding devices should be performed, by procedure, as the conductors are energized.

When installed inside equipment enclosures, temporary grounds should be lengthy enough to extend outside of the equipment so that they can be easily seen. If they cannot extend out, they should be made highly visible. Brightly colored tapes are helpful identifiers. Once they are installed, bare-hand work could be permitted.

It should be quite obvious that all personal protective grounds must be removed prior to reenergization. Identification and accountability controls may be necessary on large construction or maintenance jobs. The installation and removal of these grounding devices can be controlled by permit in order to avoid re-energizing equipment into a faulted condition.

The integrity of personal protective grounds should be maintained through the use of periodic inspection and testing. It is a good idea to document this inspection and testing.

SOLID GROUNDING OF POWER SYSTEM BASIC INFORMATION AND TUTORIALS

What is a solidly grounded system?

Solid grounding refers to the connection of the neutral of a generator, power transformer, or grounding transformer directly to the station ground or to the earth. Because of the reactance of the grounded generator or transformer in series with the neutral circuit, a solid ground connection does not provide a zero-impedance neutral circuit. 

If the reactance of the system zero-sequence circuit is too great with respect to the system positive-sequence reactance, the objectives sought in grounding, principally freedom from transient overvoltages, may not be achieved. 

This is rarely a problem in typical industrial and commercial power systems. The zero-sequence impedance of most generators used in these systems is much lower than the positive-sequence impedance of these generators. 

The zero-sequence impedance of a delta-wye transformer will not exceed the transformer's positive sequence impedance. There are, however, conditions under which relatively high zero-sequence impedance may occur.

One of these conditions is a power system fed by several generators and/or transformers in parallel. If the neutral of only one source is grounded, it is possible for the zero-sequence impedance of the grounded source to exceed the effective positive-sequence impedance of the several sources in parallel.

Another such condition may occur where power is distributed to remote facilities by an overhead line without a metallic ground return path. In this case, the return path for ground-fault current is through the earth, and, even though both the neutral of the source and the nonconducting parts at the load may be grounded with well-made electrodes, the ground return path includes the impedance of both of these ground electrodes. 

This impedance may be significant. Another significant source of zero sequence impedance is the large line-to-ground spacing of the overhead line.

To ensure the benefits of solid grounding, it is necessary to determine the degree of grounding provided in the system. A good guide in answering this question is the magnitude of ground-fault current as compared to the system threephase fault current. 

The higher the ground-fault current in relation to the three-phase fault current the greater the degree of grounding in the system. 

Effectively grounded systems will have a line-to-ground short circuit current of at least 60% of the three-phase short-circuit value. In terms of resistance and reactance, effective grounding of a system is accomplished only when R0</=X1 and X0 </= 3X1 and such relationships exist at any point in the system.

The X1 component used in the above relation is the Thevenin equivalent positive-sequence reactance of the complete system including the subtransient reactance of all rotating machines.

Application of surge arresters for grounded-neutral service requires that the system be effectively grounded.

REACTANCE GROUNDING OF POWER SYSTEM BASIC INFORMATION

What is reactance grounding? How reactance grounding is beneficial?

The term reactance grounding describes the case in which a reactor is connected between the system neutral and ground.

Since the ground-fault that may flow in a reactance-grounded system is a function of the neutral reactance, the magnitude of the ground-fault current is often used as a criterion for describing the degree of grounding.

In a reactance-grounded system, the available ground-fault current should be at least 25% and preferably 60% of the threephase fault current to prevent serious transient overvoltages (X0 </=X1).

This is considerably higher than the level of fault current desirable in a resistance-grounded system, and therefore reactance grounding is usually not considered an alternative to resistance grounding.

In most generators, solid grounding, that is, grounding without external impedance, may permit the maximum ground fault current from the generator to exceed the maximum three-phase fault current that the generator can deliver and for which its windings are braced.

Consequently, neutral-grounded generators should be grounded through a low-value reactor that will limit the ground-fault current to a value no greater than the generator three-phase fault current.

In the case of three-phase four-wire systems, the limitation of ground-fault current to 100% of the three-phase fault current is usually practical without interfering with normal four-wire operation.

In practice, reactance grounding is generally used only in this case and to ground substation transformers with similar characteristics.

LOW VOLTAGE SYSTEM EARTHING BASIC INFORMATION AND TUTORIALS

For many years the Regulations required that each l.v. system should be solidly connected to earth at only one point, that being the neutral of the source transformer. Special permission was necessary to earth at more than one point.

The Regulations also required that cables buried in the highway must have a metallic sheath. Systems earthed at only one point require the neutral conductor to be electrically separate and are now known as SNE (separate neutral and earth).

It was, and still is, the responsibility of each consumer to provide the earth connection for his own installation. This was commonly achieved by connection to a metallic pipe water main.

The growing use of PVC water mains makes this impossible for new installations and causes problems with existing ones when water mains are replaced. Gradually, supply companies developed a practice of providing consumers with an earth terminal connected to the sheath of their service cable.

This is, of course, a very satisfactory arrangement but it is not universally practical as many cables laid in the 1920s or earlier are still in use and many of these are not bonded across at joints. The arrangement is not practical on most overhead systems.

In Germany and elsewhere in Europe an earthing system known as ‘nulling’ grew up. This employed the principle of earthing the neutral at as many points as possible.

It simplified the problem of earthing in high resistance areas and by combining the sheath with the neutral conductor permitted a cheaper cable construction. These benefits were attractive and during the 1960s the official attitude in the UK gradually changed to permit and then encourage a similar system known as PME (protective multiple earthing).

Blanket approvals for the use of this system, and the required conditions to be met, were finally given to all area boards in 1974. In BS 7671 – the 16th edition of the IEE Wiring Regulations this system is classified as TN-C-S.

Providing the consumer with an earth terminal which is connected to the neutral conductor ensures that there is a low impedance path for the return of fault currents, but without additional safeguards there are possibilities of dangerous situations arising under certain circumstances.

If the neutral conductor becomes disconnected from the source of supply then the earthed metalwork in the consumer’s premises would be connected via any load to the live conductor and thus present an electric shock hazard from any metalwork not bonded to it, but which has some connection with earth. 

In order to eliminate this rare potential hazard the Secretary of State, in his official Regulations, requires that all accessible metalwork should be bonded together as specified in the IEEE Wiring Regulations and so render the consumer’s premises a ‘Faraday cage’. This is the reason for the more stringent bonding regulations associated with PME.

Under the extremely rare circumstances of a broken service neutral and intact phase conductor, there may be a danger of electric shock on the perimeter of the ‘cage’ to someone using an earthed metal appliance in a garden, even though the appliance may be protected by an RCD (residual current device) in accordance with the IEE Wiring Regulations. For the same reason metal external meter cabinets are undesirable.

In order to eliminate as far as possible the chance of a completely separated neutral, a number of precautions are taken. First, all cables must be of an approved type with a concentric neutral, either solid or stranded, of sufficient current carrying capacity.

Secondly the neutral conductor of a spur end on the system is connected to an earth electrode if more than four consumers’ installations are connected to the spur, or if the length of the spur connection from the furthest connected consumer to the distributing main exceeds 40 metres.

Where reasonably practicable, cable neutrals are joined together to form duplicate earth connections. A faulty or broken neutral will give an indication of its presence by causing supply voltages to fluctuate, which, of course, should be reported to the local DNO as soon as possible. All these measures contribute to a system which is as safe as practicable and self-monitoring.

It is the declared intention of the EI in the UK to provide earth terminals wherever required and practicable within the foreseeable future. The local DNO should be contacted regarding their requirements for the use of PME earth terminals for TN-C-S systems.

THE DANGERS OF ASBESTOS - BASIC INFORMATION AND TUTORIALS

What are the dangers of inhaling asbestos in construction?

Inhaling asbestos dust has been shown to cause the following diseases:

• asbestosis
• lung cancer
• mesothelioma (cancer of the lining of the chest and/or abdomen).

Asbestosis is a disease of the lungs caused by scar tissue forming around ve ry small asbestos fibres deposited deep in the lungs. As the amount of scar tissue increases, the ability of the lungs to expand and contract decreases, causing shortness of breath and a heavier wo rkload on the heart.

Ultimately, asbestosis can be fatal.

Lung cancer appears quite frequently in people exposed to asbestos dust.While science and medicine have not yet been able to explain precisely why or how asbestos causes lung cancer to develop, it is clear that exposure to asbestos dust can increase the risk of contracting this disease.

Studies of asbestos wo rkers have shown that the risk is roughly five times greater than for people who are not exposed to asbestos.

Cigarette smoking, another cause of lung cancer, multiplies this risk . Research has shown that the risk of developing cancer is fifty times higher for asbestos workers who smoke than for workers who neither smoke nor work with asbestos.

Mesothelioma is a relatively rare cancer of the lining of the chest and/or abdomen.While this disease is seldom observed in the general population, it appears frequently in groups exposed to asbestos.

Other illnesses—There is also some evidence of an increased risk of cancer of the stomach, rectum, and larynx. However, the link between asbestos exposure and the development of these illnesses is not as clear as with lung cancer or mesothelioma.

The diseases described above do not respond well to current medical treatment and, as a result, are often fatal.

TRANSFORMER TERMS GLOSSARY BASIC INFORMATION AND TUTORIALS

The following technical terms apply to transformers.

BIL: An abbreviation for basic impulse level, a dielectric strength test. Transformer BIL is determined by applying a high-frequency square-wave voltage with a steep leading edge between the windings and between the windings and ground.

The BIL rating provides the maximum input kV rating that a transformer can withstand without causing insulation breakdown. The transformer must also be protected against natural or man-made electrical surges. The NEMA standard BIL rating is 10 kV.

Exciting current: In transformers, the current in amperes required for excitation. This current consists of two components: (1) real in the form of losses (no load watts) and (2) reactive power in kvar. Exciting current varies inversely with kVA rating from approximately 10 percent at 1 kVA to as low as 0.5 percent at 750 kVA.

Eddy-current losses: Contiguous energy losses caused when a varying magnetic flux sets up undesired eddy currents circulating in a ferromagnetic transformer core.

Hysteresis losses: Continuous energy losses in a ferromagnetic transformer core when it is taken through the complete magnetization cycle at the input frequency.

Insulating transformer: A term synonymous with isolating transformer, to describe the insulation or isolation between the primary and secondary windings. The only transformers that are not insulating or isolating are autotransformers.

Insulation system temperature: The maximum temperature in degrees Celsius at the hottest point in the winding.

Isolating transformer: See insulating transformer.

Shielded-winding transformer: A transformer with a conductive metal shield between the primary and secondary windings to attenuate transient noise.

Taps: Connections made to transformer windings other than at its terminals. They are provided on the input side of some high-voltage transformers to correct for high or low voltages so that the secondary terminals can deliver their full rated output voltages.

Temperature rise: The incremental temperature rise of the windings and insulation above the ambient
temperature.

Transformer impedance: The current-limiting characteristic of a transformer expressed as a percentage. It is used in determining the interrupting capacity of a circuit breaker or fuse that will protect the transformer primary.

Transformer voltage regulation: The difference between the no-load and full-load voltages expressed as a percentage. A transformer that delivers 200 V at no load and 190 V at full load has a regulation of 5 percent.

GROUNDING OF ELECTRICAL EQUIPMENT SYSTEM FOR SAFETY

Grounded electrical systems are required to be connected to earth in such a way as to limit any voltages imposed by lightning, line surges, or unintentional contact with higher voltage lines. Electrical systems are also grounded to stabilize the voltage to earth during normal operation.

If, for example, the neutral of a 120/240 V, wye-connected secondary of a transformer were not grounded, instead of being 120 V to ground, the voltage could reach several hundred volts to ground. A wye-connected electrical system becomes very unstable if it is not properly grounded.

OSHA 1910.304(f)(7)(iii) Grounding of equipment. All non-current-carrying metal parts of portable equipment and fixed equipment including their associated fences, housings, enclosures, and supporting structures shall be grounded.

However, equipment that is guarded by location and isolated from ground need not be grounded. Additionally, polemounted distribution apparatus at a height exceeding 8 feet above ground or grade level need not be grounded.

In 29 CFR 1910.303, “General Requirements,” OSHA states under “(b) Examination, installation, and use of equipment (1) Examination” that “Electrical equipment shall be free from recognized hazards that are likely to cause death or serious physical harm to employees.”

This section continues with “other factors which contribute to the practical safeguarding of employees using or likely to come in contact with the equipment.” One of these “other factors” is proper grounding.

If the non-current-carrying metal parts of electric equipment are not properly grounded and these parts become energized, then any employee “using or likely to come in contact with the equipment” is at risk of an electrical shock that may or may not be fatal. This is a risk that must not be taken.

Proper grounding can effectively eliminate this shock hazard by providing a permanent and continuous low impedance path