Suitable for all technical levels, this second of three parts continues the explanation of how electrical grounding works, the functions it performs in insuring safety and proper device or equipment operation, and why it is important.
Part two of a three part series covering grounding and its role in protecting personnel, equipment, and integrity of electrical signals. This part covers the use of ground and it role in protection from ground faults. Included is a description of how a ground fault circuit interrupter (GFCI) protects personnel from severe shock. Suitable for all technical levels.
Tank Grounding for safe operating conditions to ensure proper dissipation of transient electrical currents, static electricity, and lightning dispersion.
During producing, processing, storing and transporting flammable substances (e.g. fuel, alcohol, liquid gas, explosive dusts), potentially explosive atmospheres where no ignition sources may be present to prevent explosion frequently occur in chemical and petrochemical industrial plants. The relevant safety regulations describe the risk for such plants posed by atmospheric discharges (lightning strikes). In this context, it must be observed that there is a risk of re and explosion resulting from direct or indirect lightning discharge since in some cases these plants are widely distributed.
To ensure the required plant availability and safety, a conceptual procedure is required to protect parts of electrical and electronic installations of process plants from lightning cur- rents and surges.
What is Grounding?
• Importance of Grounding
• Types of Grounding
• Applications of Grounding in power system
• Instruments employed in Grounding
• Grounding procedure & calculations
• Hazards due to lack of Grounding
• Good Grounding practice
• IEEE rules regarding Grounding
• Conclusion
Part two of a three part series covering grounding and its role in protecting personnel, equipment, and integrity of electrical signals. This part covers the use of ground and it role in protection from ground faults. Included is a description of how a ground fault circuit interrupter (GFCI) protects personnel from severe shock. Suitable for all technical levels.
Tank Grounding for safe operating conditions to ensure proper dissipation of transient electrical currents, static electricity, and lightning dispersion.
During producing, processing, storing and transporting flammable substances (e.g. fuel, alcohol, liquid gas, explosive dusts), potentially explosive atmospheres where no ignition sources may be present to prevent explosion frequently occur in chemical and petrochemical industrial plants. The relevant safety regulations describe the risk for such plants posed by atmospheric discharges (lightning strikes). In this context, it must be observed that there is a risk of re and explosion resulting from direct or indirect lightning discharge since in some cases these plants are widely distributed.
To ensure the required plant availability and safety, a conceptual procedure is required to protect parts of electrical and electronic installations of process plants from lightning cur- rents and surges.
What is Grounding?
• Importance of Grounding
• Types of Grounding
• Applications of Grounding in power system
• Instruments employed in Grounding
• Grounding procedure & calculations
• Hazards due to lack of Grounding
• Good Grounding practice
• IEEE rules regarding Grounding
• Conclusion
The complete 3-part series on best-practices for grounding electrical equipment produced by Acromag.
When wiring or connecting circuits, electrical equipment, and electrical instruments, there is a connection that you probably don’t give much thought to, and one that consequently reigns as one of the greatest sources of instrument error and malfunction. The connection is your connection to Ground.
Electrical systems must be grounded in order to work properly. The earth often serves as an ideal ground because of its large mass and ability to absorb charge, but ground can be any electrical connection that is able to freely conduct electricity, and grounding a circuit does not always refer to making a physical connection to earth ground.
SYSTEM NEUTRAL EARTHING
-DEFINITION OF SYSTEM EARTHING
-Comparative Performance For Various Conditions Using Different Earthing Methods
-EQUIPMENT SIZING
- APPENDIX FOR TYPICAL EARTHING TRANSFORMER SIZING
- APPENDIX GIVING GUIDELINE FOR SIZING OF COMMON BUS CONNECTED MEDIUM RESISTANCE EARTHING
PPT on earthing, grounding and isolation made by the students of SVIT,Vasad under the valuable guidance of the faculties teaching us Electronics and Electrical workshop(EEW) under the course of GTU.
POWER SYSTEM PROTECTION
Protection Devices and the Lightning,. protection,
Lightning protection, Introduction
Air Break Switches
Disconnect switches
Grounding switches
Current limiting reactors
Grounding transformers
Co-ordination of protective devices
Grounding of electrical installations
Electric shock
Lightning protection
Lightning Arrestor
Wintop Capital in a healthcare fund in Singapore with an objective is to achieve long-term capital appreciation through investments in healthcare sector.
The complete 3-part series on best-practices for grounding electrical equipment produced by Acromag.
When wiring or connecting circuits, electrical equipment, and electrical instruments, there is a connection that you probably don’t give much thought to, and one that consequently reigns as one of the greatest sources of instrument error and malfunction. The connection is your connection to Ground.
Electrical systems must be grounded in order to work properly. The earth often serves as an ideal ground because of its large mass and ability to absorb charge, but ground can be any electrical connection that is able to freely conduct electricity, and grounding a circuit does not always refer to making a physical connection to earth ground.
SYSTEM NEUTRAL EARTHING
-DEFINITION OF SYSTEM EARTHING
-Comparative Performance For Various Conditions Using Different Earthing Methods
-EQUIPMENT SIZING
- APPENDIX FOR TYPICAL EARTHING TRANSFORMER SIZING
- APPENDIX GIVING GUIDELINE FOR SIZING OF COMMON BUS CONNECTED MEDIUM RESISTANCE EARTHING
PPT on earthing, grounding and isolation made by the students of SVIT,Vasad under the valuable guidance of the faculties teaching us Electronics and Electrical workshop(EEW) under the course of GTU.
POWER SYSTEM PROTECTION
Protection Devices and the Lightning,. protection,
Lightning protection, Introduction
Air Break Switches
Disconnect switches
Grounding switches
Current limiting reactors
Grounding transformers
Co-ordination of protective devices
Grounding of electrical installations
Electric shock
Lightning protection
Lightning Arrestor
Wintop Capital in a healthcare fund in Singapore with an objective is to achieve long-term capital appreciation through investments in healthcare sector.
Vehicle Light Weighting - A Greener, Composite Solution (for Class A Body Pan...OC_Composites
Presentation at CAMX 2015 by Dhruv Raina, Corporate Sustainability Leader, and Michael Hiltunen of CSP, about a study on a decklid part that includes strategies for material light weighting and its impact on the environment.
Part one of a three part series covering grounding and its role in protecting personnel, equipment, and integrity of electrical signals. The first installment reviews circuit grounding and its importance, along with the use of earth ground in the US AC power system. Suitable for readers of all technical levels.
This article has been written mainly with North American users in mind, and is intended to provide readers with practical information on the operation and selection of GFCIs.
We would welcome responses to the article, favorable or otherwise, so that we can learn from our readers.
The international version of this article is entitled Demystifying RCDs and can be seen at www.rcd.ie.
See sister articles: Leakage Current Detection for AC & DC Application.
Starting With Some Acronyms
UL: Underwriters Laboratory
CSA: Canadian Standards Association
IEC: International Electrotechnical Commission
GFCI: Ground Fault Circuit Interrupter
RCD: Residual Current Device (IEC term for GFCI)
How Earthing works. What is earthing all in one for students and others? Types of Earthing. description that is needed. You can get to know how important Earthing is.
The ‘earthing’ means the connection of non-current carrying part of the equipment to the earth. When the fault occurs in the system, then the potential of the non-current part of the equipment raises, and when any human or stray animal touch the body of the equipment, then they may get shocked.
The earthing discharges the leakage current to the earth and hence avoid the personnel from the electric shock
Fiction is a form of narrative, one of the four rhetorical modes of discourse. Fiction-writing also has modes for fiction-writing: action, exposition, description, dialogue, summary, and transition (Morrell 2006, p. 127). Author Peter Selgin refers to methods, including action, dialogue, thoughts, summary, scene, and description (Selgin 2007, p. 38). Currently, there is no consensus within the writing community regarding the number and composition of fiction-writing modes and their uses.
Description is the fiction-writing mode for transmitting a mental image of the particulars of a story. Together with dialogue, narration, exposition, and summarization, description is one of the most widely recognized of the fiction-writing modes. As stated in Writing from A to Z, edited by Kirk Polking, description is more than the amassing of details; it is bringing something to life by carefully choosing and arranging words and phrases to produce the desired effect (Polking 1990, p. 106). The most appropriate and effective techniques for presenting description are a matter of ongoing discussion among writers and writing coaches.Fiction is a form of narrative, one of the four rhetorical modes of discourse. Fiction-writing also has modes for fiction-writing: action, exposition, description, dialogue, summary, and transition (Morrell 2006, p. 127). Author Peter Selgin refers to methods, including action, dialogue, thoughts, summary, scene, and description (Selgin 2007, p. 38). Currently, there is no consensus within the writing community regarding the number and composition of fiction-writing modes and their uses.
Description is the fiction-writing mode for transmitting a mental image of the particulars of a story. Together with dialogue, narration, exposition, and summarization, description is one of the most widely recognized of the fiction-writing modes. As stated in Writing from A to Z, edited by Kirk Polking, description is more than the amassing of details; it is bringing something to life by carefully choosing and arranging words and phrases to produce the desired effect (Polking 1990, p. 106). The most appropriate and effective techniques for presenting description are a matter of ongoing discussion among writers and writing coaches.Fiction is a form of narrative, one of the four rhetorical modes of discourse. Fiction-writing also has modes for fiction-writing: action, exposition, description, dialogue, summary, and transition (Morrell 2006, p. 127). Author Peter Selgin refers to methods, including action, dialogue, thoughts, summary, scene, and description (Selgin 2007, p. 38). Currently, there is no consensus within the writing community regarding the number and composition of fiction-writing modes and their uses.
Description is the fiction-writing mode for transmitting a mental image of the particulars of a story. Together with dialogue, narration, exposition, and summarization, description is one of the most widely recognized of the fiction-w
Risk in electrical work is more than any other job even using household purposes, its needs some precaution. Any slippage has no excuse. Fatal incident of a person will create a void place in his organization and family too. We can assume that working in electrical system is similar to that of work in war field. Those who are involved in electrical job they should be alert for each and every second. Mistake or failure will not be any of any excuse. Electricity is blunt and rude.In present paper we would like to enlighten some important areas which need special attention and also create awareness among the people who are working or using electrical power systems. This article is an attempt to cover most of the sub-titles of the paper.
GE's Bently Nevada 3500 Monitoring System provides continuous, online monitoring suitable for machinery protection and asset condition monitoring applications. It represents their most capable and flexible system in a traditional rack-based design and offers numerous features and advantages not provided in other systems.
Brooks Instrument Series GF40 Installation and Operation ManualFlow-Tech, Inc.
Based upon Brooks award-winning GF100 Series, the GF40 Series is a performance/value MFC platform designed for OEM applications, delivering the following class leading features:
• MultiFloTM process gas and flow range programmability, enabling customers to re-configure the MFC for new gases and full scale flow rates for unparalleled process flexibility.
• A high-performance, corrosion-resistant flow measurement sensor delivers improved reproducibility and stability.
• A variety of elastomer options enable customers to select the optimum and most cost effective mix of products for their application.
• Full range of industrial communication protocols (DeviceNet, Profibus DP-V1, and EtherCAT).
• An independent service/diagnostic port enables on-tool reconfiguration/ optimization, data logging, and troubleshooting without having to remove the MFC from the gas line.
Solving Critical Process Applications for the Water and Wastewater IndustryFlow-Tech, Inc.
Fluid Components International recognized the need for flow and level instrumentation which met specific customer requirements and demands for the Water and Wastewater Industry. By utilizing Thermal Dispersion and Coriolis technology exclusively in all FCI flow, level, interface, temperature switches and mass flow meters, our products solve typical Water and Wastewater Industry application challenges with standard product features.
Precise and easy non-invasive ultrasonic thermal energy measurement. District heating and cooling, Combined heat and power (CHP), Heating plants, Chiller plants, Sub-metering, Energy optimization, Leak Detection, Energy performance of buildings, Energy Audits, Energy Management System
Yokogawa, globally recognized leader in a number of process control fields, has authored an e-book which provides useful insight into how operators of combustion based equipment and systems can improve efficiency and enhance safety by employing modern technology.
New Class of MFCs with Embedded Flow DiagnosticsFlow-Tech, Inc.
Recent trends in multi-sensor measurements within a mass flow controller are reviewed, with a focus on controller self-diagnostics.
While the quality, reliability, accuracy, response and range of MFCs continues to improve year after year, the process is still at risk because meaningful real-time in situ data is limited or nonexistent.
Drager PointGard 2000 Series Gas Detection SystemFlow-Tech, Inc.
The Drager PointGard® 2000 series is a self-contained gas detection system for the continuous area monitoring of toxic or flammable gases in ambient air. PointGard® 2000’s rugged, water-resistant enclosure comes complete with a horn and strobes, a built-in power supply, and reliable DragerSensor®.
GE Advanced Modular Calibrator for Process Measurement InstrumentsFlow-Tech, Inc.
The DPI 620 Genii is an easy to use, rugged, and highly accurate multifunction instrument for calibrating & maintaining process instrumentation. Its modular design and functionality means it can be expanded over time and tailored to applications as needs change. With options that include HART / Fieldbus / Profibus communications, it’s a powerful, simple to use and high accuracy calibrator.
Thermal dispersion switch for flow, level, interface, or temperatureFlow-Tech, Inc.
FCI liquid level/interface switches feature thermal dispersion technology in which the temperature difference between the two RTDs is greatest in the absence of liquid and decreases when the level element is submerged, cooling the heated RTD.
FCI flow switches feature thermal dispersion technology in which the temperature difference is greatest in a no-flow condition and decreases as flow increases, cooling the heated RTD. Changes in flow velocity directly affect the extent to which heat dissipates and, in turn, the magnitude of the temperature difference between the RTDs.
Turbine flow meters for gas service from HofferFlow-Tech, Inc.
Hoffer Flow Controls manufactures high precision turbine flowmeters for the cryogenic industry and is the world leader in turbine flowmeter technology for the measurement of clean liquids and gases throughout the processing industries.
The FLUXUS G601 CA Energy is the ideal tool for carrying out complete energy efficiency tasks in the industry as well as within facility management (e.g. according to DIN ISO 50001 standards) by allowing the measurement of compressed air flow rates as well as the monitoring of thermal energy quantities and the flow rate determination of any kind of liquid or gaseous media with just one device.
Improve Process Control Security Using Annunciators as WatchersFlow-Tech, Inc.
Software-based systems are vulnerable to cyber attacks. Most of the industrial control networks (CAN, PROFI, Control Area, Ethernet and RS485) connect to the internet or other computer networks which are not fully protected from hackers and viruses. Present day industrial DCS/PLC control systems come with redun- dancy systems to eliminate shutdowns in case of DCS/PLC hardware failures. However, this does not protect your DCS/PLC system from any type of cyber attack. Without proper protection, the safety and/or operation of your plant or business are put at great risk.
Engineers with small line size processes rely on the versatile Wafer-Cone Flow Meter for superior accuracy and repeatability. The space-saving unit is easy to install. It’s ideal for tight-space installations and retrofits.
The flangeless Wafer-Cone® is compact, less costly and easy to install. The cone conditions the flow so the Wafer-Cone requires minimal upstream or downstream pipe runs and can be installed virtually anywhere in a piping system. Ideal for small line sizes and with no moving parts, no replacement parts or scheduled maintenance, this meter offers a low cost of ownership and long life.
Reduce Unplanned Outages and Improve Profitability with Asset Condition Monit...Flow-Tech, Inc.
Continuously monitoring critical asset parameters such as vibration, temperature, speed, and numerous other condition indicators is a proven method for anticipating and preventing mechanical failures—proven in tens of thousands of industrial facilities around the world by delivering tangible benefits
List of Detectable Gasses and Vapors by CAS-Number 2015Flow-Tech, Inc.
The CAS-number is a worldwide used code to identify a chemical substance non-ambiguously. This number is issued by the Chemical Abstracts Service and is the easiest way to characterize a chemical substance. Knowing the CAS-No. means to be able to get comprehensive information and links from internet and search engines.
McCrometer V Cone Flowmeter Installation, Operations, MaintenaceFlow-Tech, Inc.
The McCrometer V-Cone® Flowmeter is a patented technology that accurately measures ow over a wide range of Reynolds numbers, under all kinds of conditions and for a variety of fluids. It operates on the same physical principle as other differential pressure-type flowmeters, using the theorem of conservation of energy in fluid flow through a pipe. The V-Cone’s remarkable performance characteristics, however, are the result of its unique design. It features a centrally-located cone inside the tube. The cone interacts with the fluid flow, reshaping the fluid’s velocity profile and creating a region of lower pressure immediately downstream of itself. The pressure difference, exhibited between the static line pressure and the low pressure created downstream of the cone, can be measured via two pressure sensing taps. One tap is placed slightly upstream of the cone, the other is located in the downstream face of the cone itself. The pressure difference can then be incorporated into a derivation of the Bernoulli equation to determine the fluid flow rate. The cone’s central position in the line optimizes the velocity profile of the flow at the point of measurement, assuring highly accurate, reliable flow measurement regardless of the condition of the flow upstream of the meter.
Multivariable Transmitter for Mass Flow MeasurementFlow-Tech, Inc.
The EJX-A series is Yokogawa's premium performance line of DPharp transmitters. Field tested for over 10 years with the performance and stability demanded by industrial process control applications. The EJX910A multivariable transmitter is a remarkable innovation in multi-sensing technology. It makes optimal use of the unique characteristics of Yokogawa's DPharp sensor to provide best in class process measurement performance.
The Brooks family of extremely high-performing direct liquid injection (DLI) vaporizer solutions is designed for customers who require reliable liquid vaporization. Featuring unique atomization and heat exchanger technologies, Brooks direct liquid injection vaporizers deliver pure vapor for every application.
1. What is arc flash
2. OSHA, NFPA 70E
3. Codes and standards
4. Protective clothing and equipment
5. Prevention
An arc flash (or arc blast) is a type of electrical explosion that results from a low impedance connection to ground or another voltage phase in an electrical system
Even without electrocution, death or dismemberment may occur through an intense arc blast, up to 35,000 F deg, and force up to 2100 psi from the intense heat rapidly expanding the air, copper & particles creating a shockwave blast. Droplets of molten metal and shrapnel can penetrate the body.
Sachpazis:Terzaghi Bearing Capacity Estimation in simple terms with Calculati...Dr.Costas Sachpazis
Terzaghi's soil bearing capacity theory, developed by Karl Terzaghi, is a fundamental principle in geotechnical engineering used to determine the bearing capacity of shallow foundations. This theory provides a method to calculate the ultimate bearing capacity of soil, which is the maximum load per unit area that the soil can support without undergoing shear failure. The Calculation HTML Code included.
Hybrid optimization of pumped hydro system and solar- Engr. Abdul-Azeez.pdffxintegritypublishin
Advancements in technology unveil a myriad of electrical and electronic breakthroughs geared towards efficiently harnessing limited resources to meet human energy demands. The optimization of hybrid solar PV panels and pumped hydro energy supply systems plays a pivotal role in utilizing natural resources effectively. This initiative not only benefits humanity but also fosters environmental sustainability. The study investigated the design optimization of these hybrid systems, focusing on understanding solar radiation patterns, identifying geographical influences on solar radiation, formulating a mathematical model for system optimization, and determining the optimal configuration of PV panels and pumped hydro storage. Through a comparative analysis approach and eight weeks of data collection, the study addressed key research questions related to solar radiation patterns and optimal system design. The findings highlighted regions with heightened solar radiation levels, showcasing substantial potential for power generation and emphasizing the system's efficiency. Optimizing system design significantly boosted power generation, promoted renewable energy utilization, and enhanced energy storage capacity. The study underscored the benefits of optimizing hybrid solar PV panels and pumped hydro energy supply systems for sustainable energy usage. Optimizing the design of solar PV panels and pumped hydro energy supply systems as examined across diverse climatic conditions in a developing country, not only enhances power generation but also improves the integration of renewable energy sources and boosts energy storage capacities, particularly beneficial for less economically prosperous regions. Additionally, the study provides valuable insights for advancing energy research in economically viable areas. Recommendations included conducting site-specific assessments, utilizing advanced modeling tools, implementing regular maintenance protocols, and enhancing communication among system components.
Hierarchical Digital Twin of a Naval Power SystemKerry Sado
A hierarchical digital twin of a Naval DC power system has been developed and experimentally verified. Similar to other state-of-the-art digital twins, this technology creates a digital replica of the physical system executed in real-time or faster, which can modify hardware controls. However, its advantage stems from distributing computational efforts by utilizing a hierarchical structure composed of lower-level digital twin blocks and a higher-level system digital twin. Each digital twin block is associated with a physical subsystem of the hardware and communicates with a singular system digital twin, which creates a system-level response. By extracting information from each level of the hierarchy, power system controls of the hardware were reconfigured autonomously. This hierarchical digital twin development offers several advantages over other digital twins, particularly in the field of naval power systems. The hierarchical structure allows for greater computational efficiency and scalability while the ability to autonomously reconfigure hardware controls offers increased flexibility and responsiveness. The hierarchical decomposition and models utilized were well aligned with the physical twin, as indicated by the maximum deviations between the developed digital twin hierarchy and the hardware.
Industrial Training at Shahjalal Fertilizer Company Limited (SFCL)MdTanvirMahtab2
This presentation is about the working procedure of Shahjalal Fertilizer Company Limited (SFCL). A Govt. owned Company of Bangladesh Chemical Industries Corporation under Ministry of Industries.
Explore the innovative world of trenchless pipe repair with our comprehensive guide, "The Benefits and Techniques of Trenchless Pipe Repair." This document delves into the modern methods of repairing underground pipes without the need for extensive excavation, highlighting the numerous advantages and the latest techniques used in the industry.
Learn about the cost savings, reduced environmental impact, and minimal disruption associated with trenchless technology. Discover detailed explanations of popular techniques such as pipe bursting, cured-in-place pipe (CIPP) lining, and directional drilling. Understand how these methods can be applied to various types of infrastructure, from residential plumbing to large-scale municipal systems.
Ideal for homeowners, contractors, engineers, and anyone interested in modern plumbing solutions, this guide provides valuable insights into why trenchless pipe repair is becoming the preferred choice for pipe rehabilitation. Stay informed about the latest advancements and best practices in the field.
2. Tel: 248-295-0880 Fax: 248-624-1541 sales@acromag.com www.acromag.com
2
This paper is part two of a three part series that takes a look at grounding and its role in protecting
personnel, protecting equipment, and ensuring the integrity of electrical signals. In this part, we will
examine our use of ground as a means of protection from ground faults, and how ground fault circuit
interrupter (GFCI) devices operate to protect us from severe shock.
In part one of this series (8500-993) we looked at the concept of grounding, the AC power system and its
use of ground, and gave three main reasons why we ground electrical equipment: for safety, to stabilize
electrical signals, and to limit transient voltages and current.
Part three of this series will review ground and its role as a voltage stabilizer and transient limiter. It will
offer some tips on what you can do to improve your connection to ground to realize benefits to safety
and signal integrity.
GROUNDS AS A MEANS OF PROTECTION
In Part 1 of this series, we said that one reason we connect to ground is for safety because it provides an
alternative path for fault current to flow. The voltage in a circuit will force current to travel all available
conductive paths back to the source. The majority of this current will follow the path of least resistance.
We normally provide an earth ground connection as an alternative low-resistance path for this current
flow to limit shock (as an alternative path to using your body to return current to AC neutral and earth
ground). For AC powered circuits, a ground fault is any event that causes an imbalance in current
flowing in the AC hot lead with current flowing in the AC neutral lead. The ground fault current refers to
the difference in current flowing between AC hot and AC neutral, and it could be the current flowing in
the earth ground lead or the current taking another path back to the AC source, like through a body to
earth ground (because AC neutral and earth ground are tied together at the source).
For AC powered devices, appliance manufacturers go to great lengths to make sure that you do not
become the path of least resistance for a fault condition, which allows current to flow from AC hot back
to AC neutral/earth ground via your body (Remember that AC neutral and earth ground are held in
common at the source of the AC voltage). They do this by properly insulating their product and/or by
providing a remote connection to earth ground at the product (via that third rounded conductor at your
power outlet). That is, a conductive enclosure or housing of the device will typically connect to earth
ground. Then if the AC hot or AC neutral wire to the device should fray or break, it could contact earth
ground and complete the circuit, allowing the breaker to trip when its rated limit is reached, possibly
preventing a fire, and hopefully without electrocuting yourself in the process. Of course, some
appliances are constructed using insulating materials and do not connect their chassis to earth ground
(they connect to AC using two-prong power cords). Under normal operation, the current to the device
flows from between AC Hot and AC Neutral, through your load, and returns to your breaker box and
utility meter power connection. The third wire, or earth ground wire, will become the return path for at
least part of that current, should a fault occur at the powered device. Without this third conductor or
alternate path held in reserve, your body could become the return path of least resistance to earth
ground, and this could drive serious injury. Thus, for most 3-conductor AC wired equipment, its
connection to earth ground is primarily to provide a safe path for current to flow in the event of a circuit
fault, and normally, no current flows in the ground wire. By limiting current flow in the ground wire to
only under certain conditions (ground faults), this helps to ensure that there will be no potential
difference across this conductor, and it can better act like an extension of earth ground itself (i.e. nearly
0V).
3. Tel: 248-295-0880 Fax: 248-624-1541 sales@acromag.com www.acromag.com
3
So what does a wired earth ground really protect you from? Does it protect you from electrocution?
And what if your appliance does not include a connection to earth ground and you become the path of
least resistance for some sort of ground fault? The answer to these questions is that a wired ground
does not protect you from fatal shock. Rather, a GFCI can protect you from fatal shock.
THE GFCI AND ITS USE OF GROUND AS A MEANS OF PROTECTION FROM
GROUND FAULTS
To further illustrate how earth ground works as a means of protection, let’s
examine the behavior of a device that you may already be familiar with--the
GFCI outlet. It looks similar to the picture at left, and usually includes a “Test”
and “Reset” button. However, a GFCI protected outlet may look identical to a
standard outlet if it happens to be connected downstream to the load side of a
GFCI outlet.
You probably have several of these in your home, perhaps in your kitchen,
laundry room, basement, bathroom, garage, or at an outdoor outlet. You
probably know that these outlets are used to help protect you from severe
shock, and are generally required in “wet” areas, but you may not have given
much thought to how this device actually works with ground to help protect
you from harmful levels of shock.
For example, as ground conducts current, a voltage difference will develop across it, forcing each
connection to it to occur at a slightly different potential. So in practice, if all connections to ground were
really made at 0V, we wouldn’t have ground faults or ground loops. And therein lies the problem with
ground—your ability to mimic its idealized behavior as a reference connection to 0V really depends on
how well you can minimize its effective impedance, chiefly its resistance and inductance. Generally at
50-60Hz power line frequencies, the resistive component of your connection to earth is more significant
than the reactive component (inductance). At higher frequencies, the reactive component gains
significance, as the inductance of your connection to ground raises its impedance to transient energy.
The bottom line is that you need to minimize the effect both components have on raising ground
impedance by keeping both the resistance and inductance of your connection to ground to a minimum.
In addition to GFCI outlets, there are Ground Fault Circuit
Interrupter (GFCI) Breakers similar to the examples shown at
left. These act similar to GFCI outlets, but will protect an
entire circuit from ground faults, while the GFCI outlet only
protects at its outlet and any downstream outlets for daisy-
chained “load” outlets. The advantage of a GFCI Breaker is
that you do not need local GFCI outlets. GFCI Breakers are
typically used on circuits where the likelihood of fatal shock is
much higher (like a public swimming pool), and like a GFCI
outlet, they can typically stop current flow within 25ms of
detecting a ground fault condition on their branch circuit.
4. Tel: 248-295-0880 Fax: 248-624-1541 sales@acromag.com www.acromag.com
4
As we noted in Part 1, the AC outlets in your home commonly provide 3-wires or conductors for
connection to your appliance—a line hot connection (typically via a black insulated wire that connects to
the shorter vertical slot of the outlet), a line neutral connection (typically via a white wire that connects
to the taller vertical slot of the outlet), and a ground connection (typically via a green insulated or bare
copper wire that connects to the round hole of the outlet at the top or bottom between the two vertical
slots). In any circuit, current will seek all conductive paths back to its source, but most of this current
will flow the path of least resistance. In your home, when you plug an appliance into an AC outlet, you
give current a low-resistance path to flow through and power your appliance, and then return back via
the outlet to its source. The source in this case is where your home or business connects to the power
line, usually at your power meter and service entrance. Remember, although AC neutral and AC ground
are separate conductors at your outlet, they do connect together at your service box and also connect
to earth ground near this box, usually via one or more grounding rods driven into the earth. Load
current normally flows out the line/load hot conductor, through your appliance, and returns to earth
ground via the neutral conductor, and doesn’t normally flow in the ground conductor.
GFCI refers to a type of power outlet called a Ground Fault Current Interrupter. The GFCI outlet will
usually provide a second pair of screws for a load cable connection to allow it to connect to additional
non-GFCI outlets in daisy-chain fashion, connecting them through itself to power (making it act like a
GFCI breaker for downstream loads). This type of outlet can trip and quickly stop the flow of current
through it and downstream from it to prevent serious injury if a Ground Fault occurs anywhere in the
circuit. A Ground Fault would occur if the electricity (current) is allowed to take some other path back
to the source, than neutral (including through a person’s body), as the source is where neutral and
ground connect to the earth. A GFCI outlet works to protect you by measuring the amount of current
flowing out the “Hot” wire circuit into the appliance, and monitoring the return current flowing out of
the appliance back through the “Neutral” circuit.
If the current returned in neutral does not match the current in the hot line, the GFCI will trip and
interrupt the current flow out of the hot wire. Of course, the “lost” current doesn’t really go “missing”,
but has temporarily found some other path back to the source, perhaps through your self to earth. This
errant path is the ground fault we refer to and the GFCI feeding this circuit will trip very quickly to
prevent serious shock or electrocution via current in this errant path.
The figure at left depicts one example of a ground
faulted circuit. It shows one phase of an AC line
(like that sourced from a service panel) powering a
hand drill through a GFCI outlet or breaker. The
black AC hot wire to the hand drill makes contact
with its metallic housing (causing a ground fault),
and a workman standing on the ground and holding
the drill completes a path to earth for a portion of
the circuit current. Because this circuit was made
through a GFCI outlet or breaker, the small leakage
current triggers a relay in the black hot lead to the
drill to open and stop the flow of current, protecting the workman from severe shock.
It’s important to recognize that a GFCI does not protect against circuit overloads (too much load current),
short circuits between hot and neutral, or minor electrical shocks. The man in the example above would
still feel a small shock when he makes contact with the hand drill. And, even with a GFCI protected
circuit, you can still be shocked if you touch bare wires while standing on an insulating surface, such as a
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wood floor, and you happen to complete the neutral current path. The GFCI only protects against
current flow that does not completely follow its normal safe path along neutral to earth ground at your
service panel, but uses some other errant path to reach the earth instead. The other path could be
through a person’s body to earth ground, or even through the ground wire to earth (perhaps via a hot or
neutral short to the grounded chassis of the load device, like in the example above).
Because the GFCI outlet trips to interrupt current when it detects a ground fault (a mismatch in hot and
neutral current), it also contains a reset button used to reset its trigger mechanism. This reset has a
lockout feature that keeps it in reset for any of the following:
There is no power being supplied to the GFCI.
The GFCI has been miswired by reversing the line-in (source) and line-out (load) lead
connections.
The GFCI fails an internal test, indicating that it may not be able to provide protection from a
ground fault.
The appliance that you plug into your AC outlet typically connects its other metal parts to the ground
connection (any other conductive parts other than its AC hot and neutral circuits). It does this so that if
its own AC Hot circuit was to break or fray and accidentally come in contact with another of its metal or
conductive surfaces (like its shell or chassis), that surface would instead become a path to ground. This
path to ground essentially shorts AC hot to AC ground and causes the circuit breaker or fuse to quickly
overheat and open the circuit, interrupting the current flow. The normal level of current to cause a
typical breaker to trip is 15A or 20A, but the amount of current that can put the human heart into
fibrillation is less than 100mA. So even if a person handling that faulty appliance happened to be
barefoot and standing on wet ground, a portion of that branch current would also flow through that
person to ground and this could still be fatal.
Generally, in a ground fault situation, the body path would provide a higher resistance path to earth
than the grounded chassis and would only take a portion of this current. And just like two different
resistive loads in a circuit, current is distributed along both resistive paths, but mostly along the path of
least resistance. In the example of a grounded chassis, one path is through the ground wire and another
through the body. But, even only a small portion of that 15A or 20A of branch current that flows just
before the breaker trips is enough to stop the human heart. In the example of the hand drill, without
GFCI protection, the workman may be killed. However, if the branch circuit happens to be passing
through a GFCI protected outlet, the workman might still feel a momentary shock, but at a much lower
current and of a shorter duration, as the GFCI will interrupt the hot current flow much more quickly than
a circuit breaker alone.
In fact, a GFCI protected outlet or breaker will trip if the measured difference in current between the
“hot” and “neutral” conductors is as little as 4-6mA. Momentary contact with 120V at 6mA will shock
you, but will not likely put your heart into fibrillation, as the GFCI typically trips within 1/30th
of a second
as soon as it detects a hot/neutral imbalance, a small enough duration to protect you from fatal levels of
shock.
Also note that for the purpose of discussion, we tend to think of and talk about AC current as flowing
from the hot lead, through the device, and then returning on the neutral lead. However, AC current
does not really flow in one direction or with respect to one polarity. Rather “AC” denotes Alternating
Current, and alternating current actually flows back and forth through the load (alternating its polarity),
50-60 times a second.
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A GFCI outlet typically uses a differential or toroidal
transformer to couple the line to the load, similar to the
illustration at left. The current of the hot wire is
magnetically coupled to the toroid and then passes to the
load. The neutral wire from the load also passes through
the toroid in the opposite direction and back to the service
entrance of the house, where the line originates. These two
wires are mutually coupled via the toroid or transformer
magnetic material, such that for normal operation, the
current that flows through the hot wire balances with the
current that flows back through the neutral wire. But if
these currents do not balance, this imbalance triggers a
sensor circuit that drives relay contacts to open the Line hot
circuit (black wire), interrupting its flow. Of course, the only
way the hot and neutral line currents would not balance is if
an external source is adding current to the circuit, or the line current is being leaked through some other
external path (perhaps if line current is leaking to earth ground). A hot/neutral imbalance as small as
5mA is enough to quickly interrupt the flow of line current to the load, potentially protecting you from
fatal levels of electric shock. In this way, the GFCI interrupts the flow of current much more quickly than
the service entrance fuse or circuit breaker, in as quickly as one-thirtieth of a second.
Do not be fooled into thinking that a fuse or breaker alone can protect you from electrical shock.
Rather, it’s the purpose of a GFCI to protect you from electrical shock, while the purpose of a fuse or
breaker is to protect its premises from electrical fire by limiting the maximum current and duration of
excess current to a lower level, but not a low enough level to protect you from shock. Consider that
there are many scenarios that could cause a hot wire to accidentally come in contact with the neutral or
ground wire, causing a large amount of excess current to flow from hot to neutral. For example, an
animal might chew through the wire insulation, a person might accidentally drive a nail or screw through
the wire, or the cord connecting to an appliance might get chewed up after being pinched in a doorway
or sucked up by a vacuum cleaner. The potential fault modes are endless and difficult to prevent. These
faults will all cause excess current to flow and heat up the fuse or breaker and cause it to burn or break
open, interrupting the flow of current, possibly preventing the wire from starting a fire. The problem
with relying on a circuit breaker or fuse for shock protection is that they are tripped at much higher
levels of current (15 or 20A typical), and after longer periods of time, both of which could be fatal if you
happen to be in the path of this fault current.
We started this discussion by trying to show how a GFCI outlet works with ground to protect yourself,
but the reality is that a GFCI outlet would still protect you from electrical shock due to a ground fault,
even without a hard-wired connection to earth ground. That is, if the GFCI happened to be wired using
2-wire AC cables (hot and neutral but no earth ground), it still provides ground fault protection. This is
because a GFCI outlet monitors for current imbalances between hot and neutral, not ground. The only
possible difference in a 2-wire GFCI powered application is the ground fault current along the errant
path could potentially reach a higher level without the third wire ground path present, but the outlet
would still detect the hot-neutral imbalance and break the hot wire connection in time to protect you
from severe shock.
We spent a lot of time talking about ground as a “safe” path for current, and this is because personal
safety should be your number one priority, but we stated at the beginning of this paper that we have
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two other important reasons for connecting to ground: to stabilize signals and to limit transient voltage
and current. In Part 3 of this series, we will discuss the other two reasons we connect to ground and
give some tips for improving your connection to ground to realize the benefits of increased safety and
signal integrity for your wired equipment.
ABOUT ACROMAG
Acromag has designed and manufactured measurement and control products for more than 50 years.
They are an AS9100 and ISO 9001-certified international corporation with a world headquarters near
Detroit, Michigan and a global network of sales representatives and distributors. Acromag offers a
complete line of industrial I/O products including a variety of process instruments, signal conditioners,
and distributed fieldbus I/O modules that are available with a 2-year warranty. Industries served include
chemical processing, manufacturing, defense, energy, and water services.
For more information about Acromag products, call the Inside Sales Department at (248) 295-0880, FAX
(248) 624-9234. E-mail sales@acromag.com or write Acromag at 30765 South Wixom Road, Wixom, MI
48393 USA. The web site is www.acromag.com.
Electrical Grounding Rules Part 1 is available for download:
www.acromag.com/page/white-paper-electrical-ground-rules