explain the electrical theory of bonding and … 1 book 2/6. explain...must install a pole band on...

March 31, 2005

S T U D E N T M A N U A L

Explain the Electrical Theory of Bonding

and Grounding

Copyright 2004 by the Training and Development Centre, SaskPower. All Rights Reserved

2 S T U D E N T T R A I N I N G M A N U A L

Prerequisites: • Good knowledge and understanding of basic electricity• Explain Reasons for Temporary Bonding and Grounding• Review Series and Parallel Circuits• Explain the Hidden Dangers of the Ground Connections

Objectives: At the end of this module, the participant will be able to use electrical theory to explain non-equipotential grounding, equipotential bonding and grounding, and how an equipotential zone protects workers from dangerous voltage and current levels.

Rationale: To de-energize apparatus requires bonding and grounding and all applications are not the same. If you understand the theory, you can think electrically instead of mechanically when planning a safe de-energized work location.

Learning Objectives• Explain non-equipotential grounding using electrical theory.• Explain equipotential bonding and grounding using electrical

theory.

Learning Methods• Self-learning or Instructor Led• Self-learning or Instructor Led

EVALUATION METHODS

• Final Test• Final Test

STUDENT RESOURCES

• None

E X P L A I N T H E E L E C T R I C A L T H E O R Y O F B O N D I N G A N D G R O U N D I N G 3


Learning Steps1. Read the Learning Guide.2. Follow the steps outlined in the Learning Guide.3. Clarify any questions or concerns you may have.4. Complete the Practice and Feedback.5. Complete the Evaluation.

Introduction

Standard bonding and grounding has been carried out as an acceptedprocedure for many years to protect against unwanted current flow.There are two methods presently being used:

• Non-equipotential grounding• Equipotential bonding and grounding



Lesson 1: Non-equipotential GroundingLearning Objective:Explain non-equipotential grounding using electrical theory.Learning Method:Self-learning or Instructor LedEvaluation Method:Final Test

Non-Equipotential Grounding

Non-equipotential grounding involves grounding at the work location,or on both sides of the work location, with a long ground lead and atemporary ground electrode or rod.

Figure 1. Non-Equipotential Grounding

Using non-equipotential grounding methods, the current through andthe voltage across the electrical worker remains dangerously high; thesame as if there was no ground lead. These magnitudes areunacceptable, as the electrical worker is still prone to serious injury ordeath. The long lead serves only as a tripping ground for the protectivedevice to operate.



Circuit Calculations

Consider the circuit below as a schematic depiction of the situationabove.

Solve for Iman and Eman.

Figure 2. Powerline Technician - Example of Non-Equipotential Grounding

If your calculations are correct, you will find that the PowerlineTechnician has 877 mA (0.877 Amps) flowing through his body.



Figure 3. Powerline Technician Example Non-Equipotential Grounding with Circuit Values

Directions

Now...Compare the amps calculated to the chart titled“Physiological Reactions: Hand to Hand Current Paths” on thenext page. The reaction at 877mAis________________________________________________________________________.



Figure 4. Effects of Electrical Current on the Body



Lesson 2: Equipotential Bonding and GroundingLearning Objective:Explain equipotential bonding and grounding using electrical

theory.Learning Method:Self-learning or Instructor LedEvaluation Method:Final Test

Equipotential Bonding and Grounding

The concept of “equipotential bonding and grounding” remains thesame regardless of whether you are protecting against electromagneticinduction or powerlines that are energized in error. The only differenceis that some type of induction is present throughout most workprocedures; whereas, accidental re-energization is a rare occurance.

Circuit Calculations

Consider the last example that was pictured and schematicallyrepresented on the previous page. We will now remove the PowerlineTechnician’s standard grounds and replace them, using the approved“equipotential bonding and grounding” method.



Figure 5. Equipotential Bonding and Grounding

The Powerline Technician now has a low resistance conductoraround (parallel to) himself, which is bonded to a band below hisfeet. The band must be secured tightly to the pole in order to fullyachieve the equipotential zone. The Powerline Technician must alsobond all metallic objects to the band below his feet.

CAUTION!This would include any metallic objects brought intothe equipotential zone, such as a crane, which isbringing apparatus into the zone.



Figure 6. Bonding Uninsulated Boom into the Equipotential Zone.

This ensures that the work zone is at equipotential. There should neverbe any significant voltage across any two points within theequipotential zone and therefore no touch potential. A ground lead isbonded to the band and connected to an electrode, which is normallypositioned approximately 10 meters from the work area, 1 meter deep.

On a single structure, the Power Technician must install the polebonding device (band)1-1/2 grip-all hotstick lengths (8 foot hotstick)below the closest conductor to be grounded, which is approximately 12feet.

On two-pole structures without cross braces the Powerline Technicianmust install a pole band on each pole 1-1/2 grip-all hotstick lengths (8foot hotstick) below the closest conductor to be grounded, which isapproximately 12 feet. The two pole bands must be bonded together.

On two-pole structures (H-frame with cross braces, Gulf Port with swaybraces), the Powerline Technician must install a pole band on each poleimmediately below the cross/ sway braces on each pole. On some tall



two pole structures the cross/ sway braces may be low enough to allowfor the pole bands to be placed above the cross/ sway braces and stillallow the required 12 feet from the closest conductor to the pole band.The two pole bands must be bonded together.

This is to ensure the band(s) will be positioned below the PowerlineTechnician"s feet and that he does not have to step below the bandduring his work. Stepping below the band puts the Powerline Technicianat the risk of step and touch potential. Again, this is due to the fact thatpart of his body is out of the equipotential zone. Sometimes it may benecessary to descend the pole. Then the Powerline Technician will beat risk of either step or touch potential for the time it takes him tocompletely cross out of the equipotential zone.

We will now represent this pictorial as an electrical circuit and recordthe magnitudes of voltage and current that affects the PowerlineTechnician.

By using the rules for series and parallel circuits and Ohm’s Law, theintent is to calculate the current that will flow through the PowerlineTechnician in the event of an accidental energization.

---Note---If the Powerline Technician must cross above or below the poleband, it must be done as quickly as possible to limit the time ofexposure to the risk of step and touch potential.



Figure 7. Powerline Technician - Example Equipotential Bonding and Grounding

Figure 8. Resistance from the Conductor to Band (RA) and Band to Earth (RB)

We can now redraw the circuit as a simple series circuit to calculate thetotal resistance and the total current flowing through the entire circuit.Once we find the current flowing through the circuit we will be able tocalculate the magnitudes of current and voltage flowing through the



man.

Figure 9. Series Circuit of the Grounding Circuit

Figure 10. Total Resistance in the Series Circuit



Figure 11. Current in the Series Circuit

The Powerline Technician and the short ground lead are in parallel andwill receive the same voltage.

Figure 12. Voltage Drop Cross the Man and the Short Lead

The current flowing through the Powerline Technician’s body would be:



Figure 13. Current Flowing Through the Powerline Technician

Directions

Check the “Physiological Reactions” chart and determine theeffect of this current on the Powerline Technician. The effect is___________________________________________________________________________.



Figure 14. Different Current Flow Through the Circuit

With equipotential bonding and grounding, the Powerline Technician isin a position of relative safety because the fault current takes the path ofleast resistance.

With the band below the person’s feet bonding the pole to the conductorwith a low resistance lead, the person is in parallel with the lowresistance lead. According to the rules for parallel circuits, the personwould then receive the same voltage drop as the jumper. The lowvoltage drop would result in an almost insignificant current through thePowerline Technician.

When using equipotential grounding methods, the grounds also serve astripping ground for the protective device to operate.



Summary

To summarize this module, you have learned:

• Non-equipotential grounding is dangerous to the worker on the pole and only provides a tripping ground for the protective device to operate.

• Equipotential bonding and grounding creates an equipotential zone to protect workers on the pole from dangerous voltage and current levels.

• Equipotential bonding and grounding provides a tripping ground for the protective device to operate.

Practice Feedback

Review the lesson, ask any questions and complete the self test.

Evaluation

When you are ready, complete the final test. You are expected toachieve 100%.

Directions

Now...

1. Complete the self test.• Clarify any questions or concerns you may have.• Complete the final test.



Review Questions

T / F 1. Using the non-equipotential grounding method, the current through and the voltage across the electrical worker is reduced, therefore, making the electrical worker safe from serious injury or death.

T / F 2. The mounting location of the pole band is below the Powerline Technician’s feet.

T / F 3. To achieve the equipotential zone, the band must be secured tightly to the pole.

T / F 4. The band, coupled with short jumpers to the lines, creates an equipotential zone for the Powerline Technician who works below the band on a three phase tangent.

T / F 5. There is a possibility for step potential or touch potential if a Powerline Technician climbs out of the equipotential zone.

T / F 6. If a guy wire is brought into the equipotential zone, it must be bonded into the zone.



Review Question Solutions

1. F

2. T

3. T

4. F

5. T

6. T

explain the electrical theory of bonding and … 1 book 2/6. explain...must install a pole band on...

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