Grounding Video – Chance® (Temporary Protective Grounding)

Summary

This script emphasizes the critical importance of safety and proper temporary grounding practices for line maintenance workers, whether on live or de-energized lines. It discusses the risks of fault currents due to various causes, the role of temporary grounding in protecting workers, and the significance of creating an equipotential zone to minimize voltage drop across the worker's body. It also highlights the need for adequate grounding equipment, its correct installation, and the potential hazards faced by both overhead and ground-based line workers, advocating for adherence to industry standards and individual responsibility in ensuring safety.

Takeaways

• 🔐 Safety is paramount in line maintenance, whether on live or de-energized lines, with the goal being the safe return of all workers at the end of the day.
• ⚠️ De-energized lines are not inherently safer; accidents can still occur due to inadequate temporary grounding practices.
• 👷‍♂️ The responsibility for safety lies with the individual lineman, who must choose to follow rules and take personal responsibility for their safety.
• 🌩️ Fault currents can occur for various reasons, including human error, lightning, backfeed, accidental contact with energized circuits, and induced voltage.
• 🛡️ Temporary grounding is essential for protecting the lives of linemen, providing an equipotential zone and a low impedance path to ground to clear faults quickly.
• 🔧 Hubbell Power Systems tests temporary grounding equipment to industry standards to ensure it can handle specified fault current levels and prevent failures in the field.
• ⚡ The amount of current that can harm a lineman is minimal compared to the total fault current, emphasizing the importance of minimizing current flow through the body.
• 🔄 Current flow through a lineman's body is reduced by minimizing potential differences across the body, achieved by reducing resistance in the grounding equipment.
• 🛠️ Proper maintenance and installation of temporary grounding equipment are crucial to prevent accidents and ensure the equipment functions correctly during a fault.
• ⚙️ Selecting adequate ground sets involves understanding the maximum available fault current, its duration, and the asymmetrical factor (x over r ratio).
• 📏 The length and size of the grounding cable are important; shorter and larger cables reduce resistance and the potential current passing through the lineman.

Q & A

Why is safety emphasized for both live and de-energized line maintenance?

Safety is emphasized for both live and de-energized line maintenance because accidents can happen in both scenarios, and lives have been lost due to inadequate safety practices, such as improper temporary grounding.

What is the primary goal regarding safety for line workers?

The primary goal is for all line workers to return home alive and well at the end of their workday, which underscores the importance of following industry standards, company policies, and work rules.

What is the purpose of temporary grounding during de-energized maintenance?

The purpose of temporary grounding during de-energized maintenance is to protect the lives of line workers by providing protection against fault currents that can occur unexpectedly.

What are some reasons why fault currents can occur?

Fault currents can occur due to human error, lightning, backfeed from sources like solar panels or generators, accidental contact between de-energized and energized circuits, and induced voltage from nearby energized lines.

Why is it important to create an equipotential zone with temporary grounding?

Creating an equipotential zone with temporary grounding is important to minimize the voltage drop across the worker, reducing the current that could flow through them in the event of a fault.

What are the two essential components of proper temporary grounding?

The two essential components are creating an equipotential zone to minimize voltage drop across the worker and providing a low impedance path to ground to engage system protection devices quickly and clear the fault.

What role does Hubbell Power Systems play in ensuring temporary grounding equipment safety?

Hubbell Power Systems is a manufacturer of temporary grounding equipment that performs tests against industry standards to ensure their grounding equipment complies with specified ratings and can handle the forces associated with fault currents.

Why is it crucial to select the appropriate type of clamp for temporary grounding?

Selecting the appropriate type of clamp is crucial because different clamps are designed for specific applications and surfaces. Using the wrong clamp type can result in a poor connection, increasing the risk of equipment failure and worker injury during a fault current.

How can the current flowing through a lineman be minimized during a fault?

The current flowing through a lineman can be minimized by reducing the resistance of the temporary grounding equipment in parallel with the lineman, which in turn minimizes the potential difference across the lineman's body.

What are some key considerations for proper temporary grounding to minimize the current passing through the lineman?

Key considerations include using adequately rated grounding equipment, maintaining and taking care of the equipment, installing it properly in an equipotential configuration, and ensuring the equipment is clean and tightened to the manufacturer's recommended torque value.

What is the significance of maintaining a safe distance or using protective equipment for line workers on the ground?

Maintaining a safe distance or using protective equipment is significant for ground workers to avoid step potential and touch potential hazards, which can result in serious injury or death due to the flow of fault current through their bodies.

What is the role of an Equi-Mat in protecting ground workers during line maintenance?

An Equi-Mat helps protect ground workers by creating an equipotential surface that eliminates potential differences between the worker's feet, thus preventing current flow through their body in the event of a fault.

Outlines

00:00

🔐 Safety First in Line Maintenance

The script emphasizes the paramount importance of safety during line maintenance, whether on live or de-energized lines. It dispels the misconception that de-energized maintenance is always safer, highlighting the risks of inadequate temporary grounding that can lead to fatalities. The narrative stresses the role of individual linemen in adhering to safety rules and taking personal responsibility. It underscores the critical role of temporary grounding in protecting linemen from fault currents, which can occur due to human error, lightning, backfeed, accidental contact with energized lines, or induced voltage. The script introduces the concept of equipotential grounding and the necessity of low impedance paths for system protection devices, illustrating the potential consequences of faulty grounding with examples from Hubbell Power Systems' tests.

05:01

⚠️ Minimizing Fault Current Impact on Linemen

This paragraph delves into the dangers posed by fault currents and the measures to minimize their impact on linemen. It discusses the effects of electrical current on the human body, noting that even a small fraction of fault current can be life-threatening. The summary explains the importance of minimizing potential differences across the lineman's body by reducing resistance in the grounding equipment. It also addresses the importance of proper maintenance and installation of temporary grounding equipment, the selection of appropriate ground sets based on fault current calculations, and the significance of the x over r ratio in determining fault current asymmetry. The paragraph concludes with a warning about the risks of mechanical forces and heat from fault currents, emphasizing the need for equipment capable of handling these forces.

10:03

🛠️ Selecting and Using Adequate Temporary Grounding Equipment

The script provides detailed guidance on selecting appropriate temporary grounding equipment, stressing the importance of matching the equipment's rating to the maximum available fault current and its asymmetry. It contrasts the inadequacy of tap clamps with the necessity of using specially designed ground clamps to handle high fault currents. The paragraph also discusses the role of ferrules and heat shrink in creating low-resistance connections and protecting against mechanical forces. It advises on the selection of cable size and material, highlighting the superior current-carrying capacity of copper over aluminum, and the need to consider cable length to minimize resistance and prevent whipping effects during fault currents.

15:05

🌐 Creating an Equipotential Zone for Lineman Safety

This section of the script focuses on the concept of equipotential grounding to ensure the safety of linemen working on or near energized lines. It explains how creating an equipotential zone minimizes voltage drops across the lineman's body, reducing the risk of electric shock. The summary describes the proper installation of grounding equipment, including the use of a cluster bar and personal ground sets, to achieve this zone. It also addresses the risks associated with certain grounding configurations and the importance of maintaining clean and tight connections to ensure effective grounding. The paragraph further discusses the advantages and considerations of bracket grounding compared to single point grounding.

20:06

❄️ Earth Movement and Grounding Hazards

The script presents a visual example of the earth's movement during fault currents, emphasizing the potential hazards for anyone in the vicinity. It points out common mistakes in grounding practices, such as using loose soil for ground rods and leaving cable coiled, which can lead to dangerous situations. The paragraph also critiques outdated grounding configurations and explains the principles behind creating an equipotential zone with modern grounding techniques. It stresses the importance of minimizing cable length, ensuring clean and tight connections, and using proper grounding equipment to protect linemen from the risks of fault currents.

25:06

👥 Protecting Ground Personnel from Step and Touch Potential

This final paragraph addresses the risks faced by linemen on the ground, such as step potential and touch potential, which can result from fault currents entering the earth. The summary outlines the measures necessary to protect ground personnel, including maintaining safe distances, using equipment like the CHANCE Equi-Mat to eliminate potential differences, and employing insulating equipment suitable for the voltage levels involved. The paragraph concludes by reiterating the critical nature of proper temporary grounding for both overhead and ground workers, highlighting the life-saving impact of small changes in grounding practices.

Keywords

💡Line Maintenance

Line maintenance refers to the upkeep and repair work performed on electrical power lines. In the context of the video, it emphasizes the importance of safety whether the lines are live or de-energized. The script mentions that even though de-energized maintenance might seem safer, it still requires proper temporary grounding to prevent accidents.

💡De-energized Lines

De-energized lines are power lines that have been disconnected from their power source and are not carrying electricity. The script points out that working on de-energized lines can be safer but only if temporary grounding equipment is correctly used, highlighting the risks involved if proper safety measures are not taken.

💡Temporary Grounding

Temporary grounding is a safety practice used during line maintenance to protect workers from sudden energization or induced voltage. The video script explains that it is crucial for protecting the lives of linemen and involves creating an equipotential zone and providing a low impedance path to ground.

💡Equipotential Grounding

Equipotential grounding is the process of bonding all conductive objects in an area to minimize potential differences. The script explains that this practice is essential in creating a safe working environment for linemen by ensuring that there is no voltage drop across their body, thereby preventing electric current from flowing through them.

💡Fault Current

Fault current refers to the flow of electricity through an unintended path, often caused by a fault in the electrical system. The video script discusses various reasons for fault currents, such as human error, lightning, backfeed, and induced voltage, and the importance of being protected against them with proper temporary grounding.

💡Induced Voltage

Induced voltage is the electrical voltage that is created in a circuit due to a changing electromagnetic field from nearby energized lines. The script mentions induced voltage as a potential hazard for linemen working near energized circuits, which can lead to accidents if not properly managed with temporary grounding.

💡Asymmetry Factor (x over r ratio)

The asymmetry factor, also known as the x over r ratio, describes the wave shape of a fault current, with values indicating how much the initial peak exceeds the steady-state value. The script explains that understanding this factor is important for selecting the appropriate temporary grounding equipment capable of handling the resulting forces during a fault.

💡ASTM F855

ASTM F855 is a standard that provides specifications for temporary protective grounding of power transmission and distribution systems. The script refers to this standard as a guide for determining the required grade of grounding equipment based on the fault current levels and asymmetry factors.

💡IEC 61230

IEC 61230 is an international standard for the selection and use of temporary protective grounding equipment. The script mentions this standard in the context of testing and classifying grounding sets for different fault current levels and durations.

💡Step and Touch Potential

Step and touch potential are electrical hazards that occur when a person is standing or touching conductive surfaces during a fault current. The script discusses the risks these potentials pose to linemen on the ground and how they can be mitigated with proper protective equipment like Equi-Mats.

💡Equi-Mat

An Equi-Mat is a protective mat designed to create an equipotential zone for a lineman's feet, reducing the risk of step potential. The script highlights the importance of using Equi-Mats correctly to ensure that the lineman's feet are at the same electrical potential and are not exposed to hazardous currents.

Highlights

Safety is paramount in line maintenance, whether on live or de-energized lines.

De-energized maintenance can be safer with proper temporary grounding equipment in place.

Accidents and fatalities have occurred due to inadequate temporary grounding practices on de-energized lines.

The importance of individual responsibility in following safety rules for personal safety.

Temporary grounding for de-energized maintenance is crucial for protecting linemen's lives.

Fault currents can occur without warning, emphasizing the need for adequate equipotential grounding.

Human error, such as mistakenly closing a switch, is a common cause of fault currents.

Lightning, even from distant storms, poses a risk to linemen working on de-energized lines.

Backfeed from solar panels or generators can induce fault currents on de-energized lines.

Accidental contact between de-energized and energized circuits can lead to fault currents.

Induced voltage from nearby energized lines is a significant risk when working on de-energized lines.

The purpose of proper temporary grounding is to protect workers by creating an equipotential zone and providing a low impedance path to ground.

Fault current duration and system protection device response times are critical to prevent worker injury or death.

Hubbell Power Systems tests temporary grounding equipment against industry standards to ensure compliance and safety.

Adequate temporary grounding equipment and proper installation are vital to prevent linemen from lethal fault currents.

The amount of current flowing through a lineman during a fault is a significant concern for safety.

Studies show that very small amounts of electrical current can cause severe harm or incapacitate a person.

Minimizing the potential difference across a lineman's body is key to reducing fault current through them.

The importance of proper maintenance and testing of temporary grounding equipment to prevent failures in the field.

Selecting appropriate ground sets based on maximum available fault current and x over r ratio is crucial.

IEC 61230 and ASTM F855 are the primary industry standards for temporary protective grounding equipment.

The dangers of using tap clamps instead of proper ground clamps for temporary grounding.

Ferrules and heat shrink are essential for low resistance connections and protecting against mechanical forces.

The selection of grounding cable should consider material, size, and length to ensure adequate fault current capacity.

The risks of mechanical forces, heat, and whipping effects on grounding equipment during fault currents.

Creating an equipotential zone around the lineman is critical for minimizing current flow through the body.

The importance of using the correct type of clamp for the specific application to ensure a secure connection.

Avoiding common improper grounding configurations that can lead to increased risk for linemen.

The need for safe distances or protective equipment for ground workers to prevent step and touch potential hazards.

In summary, proper temporary grounding is essential for the safety of linemen and can prevent serious injury or death.

Transcripts

When talking about line maintenance

on live lines or de-energized lines, the same rule applies.

Safety is always first.

Many people assume that de-energized maintenance

is much safer, and in some ways it

can be if the proper temporary grounding

equipment is in place.

However, accidents do happen and lives

have been lost while working on de-energized lines

due to inadequate temporary grounding practices.

The goal is for all to return to their homes

at the end of the workday alive and well.

There are industry standards, company policies,

and work rules, but it comes down

to the individual lineman choosing to follow the rules

and taking responsibility for his own safety.

Talking about temporary grounding

for de-energized maintenance is really

talking about protecting the lives of lineman.

A lineman may work 10, or 20 years,

or even longer and never experience a fault current.

But without warning and when least expected, one can occur.

Without adequate equipotential grounding correctly installed,

the lineman can lose his life in a fraction of a second.

Temporary grounding is protection for his life.

There are a number of reasons why fault currents occur.

First, it's human error such as the closing in of a switch that

should have remained open.

Today's safety rules and procedures

are intended to eliminate human error.

However, humans make mistakes and will continue to do so.

Second, lightning is also a concern.

The storm does not have to be overhead for lightning

to strike.

In fact, it can be as much as 10 to 20 miles away.

A few years back, a utility company

was out working in their training yard.

They saw a storm off in the distance

and came down off of the poles.

Right after they had climbed into their trucks

lightning struck one of the poles they had been working on.

Third, backfeed is another concern.

There could be solar panels, a generator, or some other energy

source downstream on the circuit.

Fourth, there have been cases where a de-energized circuit

accidentally comes in contact with an energized one.

An example of this is when a car crashes into a nearby pole

and the energized circuit falls across the de-energized one.

Fifth, is induced voltage.

In the photo you will see a fluorescent lamp illuminated.

This lamp is illuminated solely by the induced voltage

from the transmission lines.

Any time when working close to another circuit that remains

energized, there is a risk of induced voltage.

Induced voltage has been the cause of many accidents.

Around the year 2000 a lineman in the USA

was killed working on a de-energized line.

There were approximately 300 volts of induced voltage

on the line from an energized 345

KB line across the right of way resulting in his death.

Whatever the reason, fault currents

have occurred and will occur.

need to be protected against them,

and this is done with proper temporary grounding.

The purpose of proper temporary grounding

is to protect the worker.

There are two essential components.

First is to create an equipotential zone

to minimize the voltage drop across the worker.

Second is to provide a low impedance

path to ground to engage the system protection devices as

quickly as possible to clear the fault.

If the fault is not cleared, the worker

could be exposed to current for a prolonged period of time

increasing the risk of injury or death.

And the fault current duration may

exceed the capacity of the temporary grounding

equipment resulting in failure.

As a manufacturer of temporary grounding equipment,

Hubbell Power Systems has performed many tests

against industry standards to ensure

chance grounding equipment complies with the specified

ratings.

Ground sets or sometimes pushed beyond their limits

to see what they are capable of handling.

This video will show what happens when ground sets fail.

Keep in mind these testing failures

were experienced in a laboratory setting to help avoid them

in the field.

If the ground sets fail, the lineman could lose his life.

For this reason, it is vital to use

adequate temporary grounding equipment

and to ensure that the equipment is properly

installed creating an equipotential zone

and providing a low impedance path to ground.

Assuming the ground equipment is adequate and does not fail,

the next concern is the amount of the current

that will flow through the lineman in contact

with the circuit during a fault current.

The fault current will divide between all paths to ground.

Some current will pass through the lineman

if he is in contact with the circuit at a second point

at a different potential.

There have been many studies conducted

on the effects of electrical current on the human body.

The results for many of these studies are quite similar.

In these studies, the results indicate

that with only 6 to 16 milliamps of current

there is a painful shock, and the person

is approaching the point of not being able to let go.

With only 17 to 99 milliamps the person

reaches the point of extreme pain, not being able to let go,

and his ability to breathe is impacted making death possible.

To look at this another way, if we had a 10,000 amp fault

current, which would fall into the lowest ASTM grade,

it is only 0.00017% of the fault current that

can put his life in jeopardy.

That is an extremely small percentage of the overall fault

current.

Because it takes so very little it is very important

to do everything possible to minimize the current that

flows through the lineman.

The key to minimizing the current that

flows through the lineman's body is

to minimize the difference in potential across his body.

This is done by minimizing the resistance

of the temporarily grounding equipment in parallel

with the lineman.

Remember, the current divides inversely proportional

to the total resistance.

Therefore, reducing the resistance

of the ground set in parallel with the lineman

will minimize the difference in potential

thus reducing the current through the lineman.

So how is this done?

There are some key considerations

for proper temporary grounding in the minimization

of the current that will pass through the lineman.

Earlier videos showed what happens

when the temporary grounding equipment is

inadequate for the level of fault current.

It is also very important to take care of,

and maintain this equipment, and to install it properly

in an equipotential configuration.

Each of these will be reviewed in detail.

There are three concerns resulting from a fault current.

Sometimes attention is only given

to the electrical current, but the resulting mechanical forces

and heat are also of great concern.

This slow motion video shows a ground set

experiencing a fault current.

The test in the video had a duration of 15 cycles

or a quarter of a second.

In real time, the cable is whipping

around so fast that there would not be time

to get out of the way.

Anyone close to the cable could be seriously injured.

There were also fireballs at both ends resulting

from the extreme heat.

The ground sets must be adequate to handle all of these forces.

By the way, this ground set passed the test.

So how are adequate ground sets selected?

The maximum available fault current and its duration

in the asymmetrical factor, or x over r ratio, must be known.

This is the fault current that the worker

must be protected against.

Although it is not uncommon for temporary ground

sets to be requested for a specific voltage

such as for 33 KV, 220 KV, or some other voltage.

It is important to remember that ground sets are rated for fault

current not for voltage.

The maximum available fault current and x over r value

will depend on many factors, including

the design of the system, proximity

to substations and generation, and other factors.

If the utility does not know the maximum available fault

current, an x over r value, it needs

to find out so adequate equipment can be selected.

They should be determined by a qualified engineer.

This should also be reviewed periodically, especially

after any system changes that could impact the maximum fault

current level.

The lowest rated component of the ground set

must be adequate to handle the maximum possible fault current.

A ground set with ASTM grade 5 clamps and ASTM grade

2 cable only provides ASTM grade 2 protection.

The amount of asymmetry in a fault current

will vary depending on the x over r value.

The asymmetry calls the initial peak

to be higher with subsequent peaks diminishing

until it reaches the asymmetrical level

or until the fault clears.

With a very low x over r value, the fault current

will be nearly symmetrical.

With the high x over r value, the peak

can be up to 2 and 1/2 times the symmetrical current or even

more.

A fault current with high asymmetry

will have substantially more severe mechanical forces

than a symmetrical fault current.

For that reason, it is very important

to understand the potential amount of asymmetry

at the worksite and ensure the temporary grounding

equipment is capable of handling the resulting forces.

The two primary industry standards

for temporary protective grounding equipment

are ASTM F855 and IEC 61230.

As these standards are periodically

reviewed and updated, please refer to the current version

for each standard.

ASTM has specific grades, 1 to 7 and 1H to 7H.

The rated and test fault current levels for these grades

are provided in two tables.

ASTM F855 table one provides withstand and ultimate fault

current levels for grades 1 to 7.

This table should be used when the asymmetry factor is

less than 20% or an x over r ratio of less

than approximately 1.8.

This is a nearly symmetrical fault current.

With a maximum available fault current level and the duration,

we can determine from the table the grade

of clamp and minimum cable size needed.

For example, with a fault current level

of 25,000 amps for less than 15 cycles,

based on withstand ratings a minimum

of grade 3 clamps with 2/0 copper cable would be needed.

ASTM F855 table 2 provides the rated

current and minimum peak current test levels

by cycle for grades 1H to 7H.

Table 2 only provides an ultimate rating

and should be used when the fault current level asymmetry

factor is greater than 20% at the worksite

or when the x over r ratio is higher than approximately 1.8.

Higher levels of asymmetry are common when working in or close

to substations but can exist in other parts of the system also.

Asymmetrical factors should always

be considered when reviewing fault current levels

for a worksite.

The testing for ASTM H grades is based on an x over r of 30.

This creates a first cycle peak of 2.69 times the

rated current.

Per IEC 61230, there are no grades.

The manufacturer may select the rated fault current level

at which they would like to classify the grounding set

and perform the testing.

For IEC testing, the symmetrical test current

is 115% of the rated current.

The current peak on the first cycle

is 2.6 times the test current for ground

sets to be used on systems over 1,000 volts

and the duration is up to 115% of the rate of duration.

For example, for a classification of 15,000 amps,

it would be almost 45,000 amps at the peak of the first cycle.

It is important to use appropriately rated ground

clamps for temporary grounding.

Tap clamps, like the one on the left, do not have the mass

and design to handle the high levels of current,

heat, and mechanical forces associated with the fault

current.

A tap clamp is designed to carry continuous current

of a few hundred or so amps, not thousands or tens of thousands

of amps that come with a fault current.

The tap clamp would be blown to pieces.

The ground clamp on the right is much larger

and has much more contact surface area

to make a lower resistance connection.

It also has two connection points

to secure the ferrule and cable.

To select clamps, first ensure the clamps

are properly tested and rated to handle

the maximum available fault current

with its corresponding asymmetry and duration.

Also select the appropriate type of clamp for the application.

For example, connecting to a flat surface

do not use C type clamps or duck bill clamps

because there will not be a good connection

and in the event of a fault current,

the clamp will very likely come off.

Instead, use a flat face or tower

clamp designed for connecting to a flat surface.

In some cases, there are options.

To connect to a round conductor there are C type, duck bill,

or all angle clamps.

In the first video, a ASTM grade 5 ball stud clamp

was tested to see if it could be rated at a higher grade.

The video is in slow motion.

In the video, the clamp was glowing red inside

from the heat and split in two as it could not

handle the heat, mechanical, and electrical forces

from this higher rating.

This is the same test but in real time.

The ferrules and heat shrink are also important.

If a bare cable is attached to a clamp,

it will have a number of issues.

First of all, when tightening the connection to the clamp,

the cable strands could be damaged.

It may only take a few broken strands to significantly impact

the current carrying capability of the cable resulting

in a failure.

Over time, the movement and handling

would also damage more cable strands.

Second, there would also be oxidation and contamination

all resulting in a higher resistance connection.

The damaged cable would not meet the cables original rating,

and it may ultimately fail.

The higher resistance or failure could result in serious injury

or death for the lineman.

Third, ferrules are used to make a solid low resistance

connection.

In the photo in the bottom right hand corner,

it is not visible where the ferrule ends

and the cable begins.

In the photo just to the left, the difference

can be seen because it is an aluminum ferrule.

Fourth, the ferrules also help to absorb

some of the mechanical force as shown in this slow motion

video.

As the mechanical force came down, the ferrule bent.

It takes a significant amount of force to bend that ferrule.

The ferrule bending absorbed some of the mechanical force,

so it did not all impact the clamp.

The heat shrink is also important.

It helps keep out moisture and contaminants

resulting in less corrosion and resistance.

It also provides stress relief for the cable.

The heat shrink adds rigidity where

the cable enters the ferrule while still allowing some bend.

This helps absorb some of the mechanical forces.

In addition for an unshrouded ferrule,

it minimizes the bending where the copper strands of the cable

are in contact with the edge of the ferrule.

The cable should also be rated for the maximum level

of available fault current with its corresponding asymmetry

and duration.

As discussed earlier, we need a low impedance connection

to ground to operate the system devices

and clear the fault current as quickly as possible.

If the fault current does not clear,

the heat will continue to increase,

and the cable could reach its fusing point

in a matter of cycles.

This first video will show what happens

when a cable is undersized or what

may happen if the fault current does not clear.

It is very evident from this video

that an undersized cable will fail quickly and leave

the lineman unprotected.

Standard grounding cable per ASTM F855

should be stranded soft drawn copper conductor.

The IEC 61230 standard allows for copper aluminum

or aluminum alloy.

However, per IEC 61230 the selection of aluminum cable

should be made carefully and include precautions for storage

and inspections before use.

These additional precautions are necessary because aluminum

damages more easily.

The current carrying capacity of aluminum versus copper

must also be considered when selecting cable size.

Based on information provided in IEC 61230

and as seen in this table for a 95 millimeter squared aluminum

cable, the current carrying capacity

would only be 16,700 amps versus 25,500 amps for copper.

That is less than 2/3 the current carrying

capacity of the copper cable.

In other words, to have the equivalent current carrying

capacity you would need a larger aluminum cable.

For these reasons, Hubbell Power Systems, as a manufacturer,

only recommends soft drawn copper cable.

The length of the cable must also be considered.

It is important to minimize the cable length because resistance

increases with length.

However, that does not mean the cable should be taut.

If it is taut, the mechanical forces could break it.

Some slack is needed.

The IEC 61230 guidelines recommend

the cable should be between 1.2 and 1.5 times the distance

between the installed clamps.

The cable length should also be taken into consideration

because of the whipping effect that

can result from excess cable during the fault current.

Whipping cable can hit and injure a person

or impact the structure resulting in damage to

and potential failure of the cable.

The whipping effect can also increase the mechanical forces

and result in a failure as seen in this slow motion video.

The cable came up and then back down just like a whip,

and the cable failed right at the cracking point.

This happened in less than a fourth of a second.

As a side note, this was a new type of cable

that Hubbell Power Systems had not tested previously.

The engineer running these tests believes

the cable failed because it may have had broken strands.

The following slides will show that the cable length can

mean the difference between going home for the day

and possibly losing your life because of the increased

resistance resulting from longer cable.

In this example, a ground set with a three meter 1/0 copper

cable is being used to protect against a 10,000 amp fault

current.

Based on Kirchhoff's law, the current

that would pass through lineman is 13 milliamps.

If the cable length is increased to 7.6 meters with the same 1/0

copper cable and 10,000 amp fault current,

the current passing through the lineman

increases to 27.7 milliamps.

His life is now in danger.

For this reason, the cable link should

be minimized allowing for some slack as previously discussed.

The cable size also makes a difference.

With the 1/0 cable that was in the first example,

there were 13 milliamps passing through the lineman.

If the cable is replaced by a larger 4/0 cable, which

has less resistance, the current passing through the lineman

is reduced to 8.4 milliamps.

The larger cable provides better protection.

However, it also weighs more.

If close to the limit of a grading or rating,

consideration should be given to using a larger cable size.

The care, maintenance, and testing

of temporary grounding equipment are also very important.

IEC 61230 states that temporary grounding equipment

should be thoroughly inspected before each use.

If any damage is detected, it should be removed from service.

In addition, ground sets should be tested periodically

with a tester such as the CHANCE temporary ground set tester.

The ASTM and IEC standards do not

specify the frequency for testing temporary grounding

equipment.

As a manufacturer, Hubbell Power Systems

recommends testing at least once every 12 months.

However, the employer should determine

if more frequent testing should be performed

taking into consideration the frequency of use,

work conditions, care and maintenance, et cetera.

Frequently, ground sets fail testing due to dirty clamps.

Contamination and oxidation on the clamps

increase the resistance.

If these ground sets are failing when tested,

that means they are not offering the protection

they should in the field.

This could mean the difference between surviving

a fault current or not.

For this reason, ground sets should be kept clean.

The contact surfaces should be cleaned with a wire brush

before each use.

There are some key points to remember when installing

temporary grounding equipment.

As already discussed, the ground sets

need to be thoroughly inspected before each use.

The lineman needs to verify that the line is de-energized

and should clean the clamp and all

contacting surfaces such as the conductor, ball stud, or bus

to minimize the resistance that can result from oxidation

and contamination.

He should also ensure that the clamps

are tightened to the manufacturer's recommended

torque value.

In case of a fault current, the added resistance

from contamination or from loose clamps

could result in serious injury or death.

It only takes a few minutes to clean and tighten

the connections.

When installing the clamps, always

treat the system as energized until it is 100% grounded.

This means using an insulated stick such as a CHANCE Grip-All

Clampstick when installing clamps on the conductors.

Always connect to the ground connection

first and remove the ground connection last.

Also make sure the ground connection is clean, tightened,

and properly sized.

For example, if connecting to a ball stud,

makes sure the ball stud is adequately sized and tightened.

This slow motion video shows what

happens when the ball stud is undersized.

The undersized ball stud failed.

This next video shows what it looks like when the fault

current enters the earth.

This video is a little older, but the content

is still applicable today.

The earth appears white because it is covered with snow.

The earth is frozen, at least before the tests.

These tests are all at around 3,000 amps.

It is amazing how the earth moves,

and clearly there is a hazard for anyone nearby.

Here's an example of what not to do.

This driven ground rod is clearly in loose soil

and would likely come flying out of the ground in the event

of a fault current.

It is also important to note that there is some cable still

coiled on the reel.

Coiled cable acts as an inductor and could melt, vaporize,

or explode.

Always remove all cable from a reel when installing.

Now a look at configurations.

Here are four configurations that at times in the past,

and hopefully not at the present, were commonly used.

These four configurations are not adequate.

In the first, each phase is grounded to its own ground rod.

In the second, all three phases are grounded to the same ground

rod.

In to third, the three phases are connected up top

and have a single ground set from one phase connected

to a ground rod.

In the fourth, the three phases are connected up top

and have a single ground set to the neutral.

So what are the issues with these configurations?

First of all, in the first three configurations,

the cables are very long.

Looking at the calculations for this example,

with a 12.2 meter cable, there are 42.4 milliamps

passing through the lineman.

This is much too high and could result in death.

Second, the voltage drop across the lineman's body

has not been minimized.

The lineman is at a different potential than the grounds,

and his hands and feet are at different potentials.

An equipotential zone is created by bonding

all conductive objects together at the work site

to minimize the differences in potential.

Remember, to minimize the differences in potential,

we need to minimize the resistance of the ground sets

connecting the conductive objects.

On a pole this is done by adding a cluster bar under and close

to the lineman's feet, and installing

a ground set from the cluster bar to the phase

he is working on, and bonding to any other conductive

object in the work area, such as a guide wire.

In the example, the cable in parallel with the lineman

is now reduced only three meters.

The current through the lineman per Kirchhoff's law

is reduced to 13 milliamps.

This is a big improvement over the 42.4 milliamps.

Equipotential zone around the lineman

puts his hands at nearly the same potential as his feet.

If his hands and feet are at the same potential,

there is no voltage drop across his body,

and the current does not flow through his body.

In reality, there will always be a slight difference

in the potential between his hands and feet

and some current will flow through the lineman.

However, by using equipotential grounding,

we minimize the current through his body

as much as possible by reducing the resistance

of the parallel path and thus minimizing

the difference in potential.

When climbing on wood poles, the clustered bar

should always be in conductive contact

with a metal nail or spike that penetrates the pole at least as

far as the climbing gaffs.

This is to bond to the potentially more conductive

interior of the pole.

For steel lattice towers, the equipotential zone

is created by grounding each phase to the metal structure

below the lineman.

All connections need to be clean and tight.

Bracket grounding is used in many places around the world.

That is grounding installed on both sides of the work site.

Using bracket grounding, also known

as double point grounding, has some advantages

over single point grounding.

However, consideration should be given

to the risk of creating a current loop.

If using bracket grounding to create an equipotential zone,

it is critical for the lineman to install a cluster bar below

and close to his feet on the pole he is working on

and also a personal ground set from the cluster bar

to the phase he is touching.

Without the clustered bar and personal grounds set,

there is no equipotential zone, and the lineman

may be exposed to hazardous differences

in electrical potential from induced voltage

or in case of a fault current.

The advantages of double point versus single point grounding

are--

first, the double point provides an additional low resistance

path the ground allowing more of the current

to flow through the grounds thus reducing the current that

would flow through the lineman.

Remember, the current will divide

between all paths to ground, so an additional path

will reduce the current through the lineman.

Second, most of the current flows

to the ground farther away from the work site

reducing the risk of step and touch potential

at the work structure.

The advantages of single point are: first, less time

and work to install the temporary grounding

equipment as there are fewer ground sets to install

and only one structure involved; second, the ground sets

are in closer proximity and more easily monitored.

It is also important to mention that equipotential grounding is

still required when working from an insulated bucket truck.

Any contact with the pole or cross arm

while working on the conductor creates a path

to ground through the worker.

Up until this point, the discussion

has been mostly about the protection of the lineman

working overhead.

There are risks for the lineman on the ground also,

and they need to be protected.

The first of these risks is step potential.

When the fault current enters the earth,

it will generally decrease in magnitude

with the distance from the entry point due to the soil

resistivity.

Anyone without protection standing with their feet

apart and close to the entry point

will have a difference in potential between their feet

resulting in current flow through their body.

The current will enter one foot and exit the other.

Accidents of this nature have happened

resulting in burns, amputations, and worse.

In one particular case, the lineman on the ground

was 8.5 meters away and had significant injuries.

Safe distances will be discussed in more detail shortly.

There is also the risk of touch potential.

If the unprotected lineman is touching the structure,

the truck or any other conductive

object that becomes energized or in the fault

the lineman is another path to ground.

The ground resistance will vary from place to place and even

within the work zone.

In this example, the earth resistance

is 32 ohmmeters with a fault current of 10,000 amps entering

the earth.

As shown, the current diminishes as the distance increases.

Taking a closer look in this example,

to keep the current through the lineman

at or below 16 milliamps, the distance

would be almost 15 meters.

This is a significant distance.

The are lineman on the ground who are exposed to these risks.

They either need to maintain a safe distance, which

in many cases is not practical or have protection.

A CHANCE Equi-Mat is one option.

With both feet on the properly installed Equi-Mat,

the difference in potential is virtually eliminated,

and the lineman is protected.

It is critical, though, for the lineman

not to have one foot on the mat and the other foot

on the ground as his feet would be at different potentials.

The Equi-Mats come in different sizes

and can be connected together to make a larger protected work

area.

Insulating equipment adequate for the maximum voltage

is another option.

In summary, proper temporary grounding

creates an equipotential zone providing the best known

protection for the lineman.

Small changes such as shorter cable links,

cleaning the clamps, cleaning the conductors, et cetera,

affect resistance and the current through the lineman.

These small changes can make the difference

between a lineman suffering serious injury or death

or going home for the day.

Proper temporary grounding is critical.

The safety of the lineman must come first.