California Code of Regulations › Title 8 - Industrial Relations › Division 1 - Department of Industrial Relations › Chapter 4 - Division of Industrial Safety › Subchapter 5 - Electrical Safety Orders › Group 2 - High-Voltage Electrical Safety Orders › Article 36 - Work Procedures and Operating Procedures › Appendix A - Working on Exposed Energized Parts

Current through Register 2024 Notice Reg. No. 28, July 12, 2024
I. Introduction
Electric utilities design electric power generation,
						  transmission, and distribution installations to meet National Electrical Safety
						  Code (NESC), ANSI C2, requirements. Electric utilities also design transmission
						  and distribution lines to limit line outages as required by system reliability
						  criteria [FN1] and to withstand the maximum overvoltages impressed on the
						  system. Conditions such as switching surges, faults, and lightning can cause
						  overvoltages. Electric utilities generally select insulator design and lengths
						  and the clearances to structural parts so as to prevent outages from
						  contaminated line insulation and during storms. Line insulator lengths and
						  structural clearances have, over the years, come closer to the minimum approach
						  distances used by workers. As minimum approach distances and structural
						  clearances converge, it is increasingly important that system designers and
						  system operating and maintenance personnel understand the concepts underlying
						  minimum approach distances.
The information in this appendix will assist employers
						  in complying with the minimum approach-distance requirements contained in
						  Section 2940.2. Employers shall use the
						  technical criteria and methodology presented in this appendix in establishing
						  minimum approach distances in accordance with Section
						  2940.2(c) and
						  Table 2940.2-1 and Table 2940.2-6. This appendix provides essential background
						  information and technical criteria for the calculation of the required minimum
						  approach distances for live-line work on electric power generation,
						  transmission, and distribution installations.
Unless an employer is using the maximum transient
						  overvoltages specified in Table 2940.2-5 for voltages over 72.5 kilovolts, the
						  employer shall use persons knowledgeable in the techniques discussed in this
						  appendix, and competent in the field of electric transmission and distribution
						  system design, to determine the maximum transient overvoltage.
II. General
A.
Definitions
. The following
						  definitions from Section
						  2700 relate to work on or near
						  electric power generation, transmission, and distribution lines and equipment
						  and the electrical hazards they present.
Exposed. Not isolated or guarded.
Guarded. Covered, shielded, fenced, enclosed, or
						  otherwise protected by means of suitable covers, casings, barriers, rails,
						  screens, mats, or platforms to remove the likelihood of approach to a point of
						  danger or contact by persons or objects.
NOTE to the definition of "guarded": Wires that are
						  insulated, but not otherwise protected, are not guarded.
Insulated. Separated from other conducting surfaces by
						  a dielectric (including air space) offering a high resistance to the passage of
						  current.
NOTE to the definition of "insulated": When any object
						  is said to be insulated, it is understood to be insulated for the conditions to
						  which it normally is subjected. Otherwise, it is, for the purpose of this
						  section, uninsulated.
Isolated (as applied to location). Not readily
						  accessible to persons unless special means for access are used.
Statistical Sparkover Voltage. A transient overvoltage
						  level that produces a 97.72-percent probability of sparkover (that is, two
						  standard deviations above the voltage at which there is a 50-percent
						  probability of sparkover).
Statistical Withstand Voltage. A transient overvoltage
						  level that produces a 0.14-percent probability of sparkover (that is, three
						  standard deviations below the voltage at which there is a 50-percent
						  probability of sparkover).
B.
Installations energized at 50 to 300
						  volts
. The hazards posed by installations energized at 50 to 300 volts
						  are the same as those found in many other workplaces. That is not to say that
						  there is no hazard, but the complexity of electrical protection required does
						  not compare to that required for high voltage systems. The employee shall avoid
						  contact with the exposed parts, and the protective equipment used (such as
						  rubber insulating gloves) shall provide insulation for the voltages
						  involved.
C.
Exposed energized parts over 600 volts
						  AC
. Section
						  2940.2 (a)
						  requires the employer to establish minimum approach distances no less than the
						  distances computed by Table 2940.2-1 for ac systems so that employees can work
						  safely without risk of sparkover. [FN2]
Unless the employee is using electrical protective
						  equipment, air is the insulating medium between the employee and energized
						  parts. The distance between the employee and an energized part shall be
						  sufficient for the air to withstand the maximum transient overvoltage that can
						  reach the worksite under the working conditions and practices the employee is
						  using. This distance is the minimum air insulation distance, and it is equal to
						  the electrical component of the minimum approach distance.
Normal system design may provide or include a means
						  (such as lightning arrestors) to control maximum anticipated transient
						  overvoltages, or the employer may use temporary devices (portable protective
						  gaps) or measures (such as preventing automatic circuit breaker reclosing) to
						  achieve the same result. Subsection (a)(1) of Section
						  2940.2 requires the employer to
						  determine the maximum anticipated per-unit transient overvoltage,
						  phase-to-ground, through an engineering analysis or assume a maximum
						  anticipated per-unit transient overvoltage, phase-to-ground, in accordance with
						  Table 2940.2-5, which specifies the following maximums for ac systems:
72.6 to 420.0 kilovolts-3.5 per unit
420.1 to 550.0 kilovolts-3.0 per unit
550.1 to 800.0 kilovolts-2.5 per unit
See Section IV.A.2, later in this appendix, for
						  additional discussion of maximum transient overvoltages.
D.
Types of exposures
. Employees
						  working on or near energized electric power generation, transmission, and
						  distribution systems face two kinds of exposures: Phase to-ground and
						  phase-to-phase. The exposure is phase-to-ground: (1) With respect to an
						  energized part, when the employee is at ground potential or (2) with respect to
						  ground, when an employee is at the potential of the energized part during
						  live-line barehand work, which requires a permanent variance. The exposure is
						  phase-to phase, with respect to an energized part, when an employee is at the
						  potential of another energized part (at a different potential) during live-line
						  barehand work.
III. Determination of Minimum Approach Distances
						  for AC Voltages Greater Than 300 Volts
A. Voltages of 301 to 5,000 volts. Test data generally
						  forms the basis of minimum air insulation distances. The lowest voltage for
						  which sufficient test data exists is 5,000 volts, and these data indicate that
						  the minimum air insulation distance at that voltage is 20 millimeters (1 inch).
						  Because the minimum air insulation distance increases with increasing voltage,
						  and, conversely, decreases with decreasing voltage, an assumed minimum air
						  insulation distance of 20 millimeters will protect against sparkover at
						  voltages of 301 to 5,000 volts. Thus, 20 millimeters is the electrical
						  component of the minimum approach distance for these voltages.
B. Voltages of 5.1 to 72.5 kilovolts. For voltages from
						  5.1 to 72.5 kilovolts, the Department of Labor, Occupational Safety and Health
						  Administration bases the methodology for calculating the electrical component
						  of the minimum approach distance on Institute of Electrical and Electronic
						  Engineers (IEEE) Standard 4-1995, Standard Techniques for High-Voltage Testing.
						  Table 1 lists the critical sparkover distances from that standard as listed in
						  IEEE Std 516-2009, IEEE Guide for Maintenance Methods on Energized Power
						  Lines.
TABLE 1-SPARKOVER DISTANCE
									 FOR ROD-TO-ROD GAP
60 Hz Rod-to-Rod
									 sparkover (kV peak)
Gap spacing from
									 IEEE Std 4-1995 (cm)
25
2
36
3
46
4
53
5
60
6
70
8
79
10
86
12
95
14
104
16
112
18
120
20
143
25
167
30
192
35
218
40
243
45
270
50
322
60
Source: IEEE Std 516-2009.
To use this table to determine the electrical component
						  of the minimum approach distance, the employer shall determine the peak
						  phase-to-ground transient overvoltage and select a gap from the table that
						  corresponds to that voltage as a withstand voltage rather than a critical
						  sparkover voltage. To calculate the electrical component of the minimum
						  approach distance for voltages between 5 and 72.5 kilovolts, use the following
						  procedure:
1. Divide the phase-to-phase voltage by the square root
						  of 3 to convert it to a phase-to-ground voltage.
2. Multiply the phase-to-ground voltage by the square
						  root of 2 to convert the rms value of the voltage to the peak phase-to-ground
						  voltage.
3. Multiply the peak phase-to-ground voltage by the
						  maximum per-unit transient overvoltage, which, for this voltage range, is 3.0,
						  as discussed later in this appendix. This is the maximum phase-to-ground
						  transient overvoltage, which corresponds to the withstand voltage for the
						  relevant exposure. [FN3]
4. Divide the maximum phase-to-ground transient
						  overvoltage by 0.85 to determine the corresponding critical sparkover voltage.
						  (The critical sparkover voltage is 3 standard deviations (or 15 percent)
						  greater than the withstand voltage.)
5. Determine the electrical component of the minimum
						  approach distance from Table 1 through interpolation.
Table 2 illustrates how to derive the electrical
						  component of the minimum approach distance for voltages from 5.1 to 72.5
						  kilovolts, before the application of any altitude correction factor, as
						  explained later.
TABLE 2-CALCULATING THE
									 ELECTRICAL COMPONENT OF MAD 751 V TO 72.5 kV
Step
Maximum system
									 phase-to-phase voltage (kV)
15
36
46
72.5
1. Divide by
								  Y3
8.7
20.8
26.6
41.9
2. Multiply by
								  Y2
12.2
29.4
37.6
59.2
3. Multiply by
								  3.0.
36.7
88.2
112.7
177.6
4. Divide by
								  0.85.
43.2
103.7
132.6
208.9
5. Interpolate from Table 1.
3+(7.2/
								  10)*1
14+(8.7/ 9)*2
20+(12. 6/23)*5
35+(16.
								  9/26)*5
Electrical component of MAD
								  (cm)
3.72
15.93
22.74
38.25
C. Voltages of 72.6 to 800 kilovolts. For voltages of
						  72.6 kilovolts to 800 kilovolts, this section bases the electrical component of
						  minimum approach distances, before the application of any altitude correction
						  factor, on the following formula:
Equation 1-For Voltages of 72.6 kV to 800 kV
D
= 0.3048(C + a)
						  VL%-GT
Where:
D
= Electrical component of the
						  minimum approach distance in air in meters;
C =
a correction factor associated
						  with the variation of gap sparkover with voltage;
a
= A factor relating to the
						  saturation of air at system voltages of 345 kilovolts or higher; [FN4]
VL-G = Maximum system
						  line-to-ground rms voltage in kilovolts-it should be the "actual" maximum, or
						  the normal highest voltage for the range (for example, 10 percent above the
						  nominal voltage); and
T
= Maximum transient overvoltage
						  factor in per unit.
In Equation 1,
C
is 0.01: (1) For
						  phase-to-ground exposures that the employer can demonstrate consist only of air
						  across the approach distance (gap) and (2) for phase-to phase exposures if the
						  employer can demonstrate that no insulated tool spans the gap and that no large
						  conductive object is in the gap. Otherwise,
C
is 0.011.
In Equation 1, the term
a
varies
						  depending on whether the employee's exposure is phase-to-ground or
						  phase-to-phase and on whether objects are in the gap. The employer shall use
						  the equations in Table 3 to calculate
a
. Sparkover test data
						  with insulation spanning the gap form the basis for the equations for
						  phase-to-ground exposures, and sparkover test data with only air in the gap
						  form the basis for the equations for phase-to phase exposures. The
						  phase-to-ground equations result in slightly higher values of a, and,
						  consequently, produce larger minimum approach distances, than the
						  phase-to-phase equations for the same value of
						  VPeak.
TABLE 3-EQUATIONS FOR
									 CALCULATING THE SURGE FACTOR,
a
Phase-to-ground
									 exposures
VPeak =
								  TL-GVL-GY2
635 kV or less
								  0
635.1 to 915
915.1 to 1,050
___________________________
kV
								  (VPeak-635)
kV
								  (VPeak-645
/140,000
/135,000
A
VPeak =
								  TL-GVL-GY2
More than
								  1,050 kV
A
(VPeak-675)/125,000
Phase-to-phase
								  exposures1
VPeak =
								  (1.35TL-G +
								  0.45)VL-GY2
630 kV or less 0
630.1 to
								  848 kV (VPeak-630)
848.1 to 1,131 kV
								  (VPeak-633.6) /152,207
a
/155,000
-633.6)/
								  152,207
VPeak =
								  (1.35TL-G +
								  0.45)VL-GY2
1,131.1 to 1,485 kV
								  (VPeak-628) /153,846
More than 1,485
								  kV (VPeak-350.5)/203,666
a
/153,846
1 Use the equations for
						  phase-to-ground exposures (with VPeak for phase-to-phase
						  exposures) unless the employer can demonstrate that no insulated tool spans the
						  gap and that no large conductive object is in the gap.
In Equation 1, T is the maximum transient overvoltage
						  factor in per unit. As noted earlier, Section
						  2940.2 (a)(1)(A)
						  requires the employer to determine the maximum anticipated per-unit transient
						  overvoltage, phase-to-ground, through an engineering analysis or assume a
						  maximum anticipated per-unit transient overvoltage, phase-to-ground, in
						  accordance with Table 2940.2-5. For phase-to-ground exposures, the employer
						  uses this value, called TL-G, as T in Equation 1. IEEE Std 516-2009 provides
						  the following formula to calculate the phase-to-phase maximum transient
						  overvoltage, TL-L, from TL-G:
TL-L =
						  1.35TL-G + 0.45
For phase-to-phase exposures, the employer uses this
						  value as T in Equation 1.
D.
Provisions for inadvertent
						  movement
. The minimum approach distance shall include an "adder" to
						  compensate for the inadvertent movement of the worker relative to an energized
						  part or the movement of the part relative to the worker. This "adder" shall
						  account for this possible inadvertent movement and provide the worker with a
						  comfortable and safe zone in which to work. Employers shall add the distance
						  for inadvertent movement (called the "ergonomic component of the minimum
						  approach distance") to the electrical component to determine the total safe
						  minimum approach distances used in live-line work.
The US Department of Labor, Occupational Safety and
						  Health Administration based the ergonomic component of the minimum approach
						  distance on response time-distance analysis. This technique uses an estimate of
						  the total response time to a hazardous incident and converts that time to the
						  distance traveled. For example, the driver of a car takes a given amount of
						  time to respond to a "stimulus" and stop the vehicle. The elapsed time involved
						  results in the car's traveling some distance before coming to a complete stop.
						  This distance depends on the speed of the car at the time the stimulus appears
						  and the reaction time of the driver.
In the case of live-line work, the employee shall first
						  perceive that he or she is approaching the danger zone. Then, the worker
						  responds to the danger and shall decelerate and stop all motion toward the
						  energized part. During the time it takes to stop, the employee will travel some
						  distance. This is the distance the employer shall add to the electrical
						  component of the minimum approach distance to obtain the total safe minimum
						  approach distance.
At voltages from 751 volts to 72.5 kilovolts, [FN5] the
						  electrical component of the minimum approach distance is smaller than the
						  ergonomic component. At 72.5 kilovolts, the electrical component is only a
						  little more than 0.3 meters (1 foot). An ergonomic component of the minimum
						  approach distance shall provide for all the worker's unanticipated movements.
						  At these voltages, workers generally use rubber insulating gloves; however,
						  these gloves protect only a worker's hands and arms. Therefore, the energized
						  object shall be at a safe approach distance to protect the worker's face. In
						  this case, 0.61 meters (2 feet) is a sufficient and practical ergonomic
						  component of the minimum approach distance.
For voltages between 72.6 and 800 kilovolts, employees
						  shall use different work practices during energized line work. Generally,
						  employees use live-line tools (hot sticks) to perform work on energized
						  equipment. These tools, by design, keep the energized part at a constant
						  distance from the employee and, thus, maintain the appropriate minimum approach
						  distance automatically.
The location of the worker and the type of work methods
						  the worker is using also influence the length of the ergonomic component of the
						  minimum approach distance. In this higher voltage range, the employees use work
						  methods that more tightly control their movements than when the workers perform
						  work using rubber insulating gloves. The worker, therefore, is farther from the
						  energized line or equipment and shall be more precise in his or her movements
						  just to perform the work. For these reasons, this section adopts an ergonomic
						  component of the minimum approach distance of 0.31 m (1 foot) for voltages
						  between 72.6 and 800 kilovolts.
Table 4 summarizes the ergonomic component of the
						  minimum approach distance for various voltage ranges.
TABLE 4-ERGONOMIC
									 COMPONENT OF MINIMUM APPROACH DISTANCE
Distance
Voltage range
									 (kV)
m
ft
0.301 to 0.750
0.31
1.0
0.751 to 72.5
0.61
2.0
72.6 to 800
0.31
1.0
NOTE: The employer shall add this distance to the
						  electrical component of the minimum approach distance to obtain the full
						  minimum approach distance.
The ergonomic component of the minimum approach
						  distance accounts for errors in maintaining the minimum approach distance
						  (which might occur, for example, if an employee misjudges the length of a
						  conductive object he or she is holding), and for errors in judging the minimum
						  approach distance. The ergonomic component also accounts for inadvertent
						  movements by the employee, such as slipping. In contrast, the working position
						  selected to properly maintain the minimum approach distance shall account for
						  all of an employee's reasonably likely movements and still permit the employee
						  to adhere to the applicable minimum approach distance. (See Figure 1.)
						  Reasonably likely movements include an employee's adjustments to tools,
						  equipment, and working positions and all movements needed to perform the work.
						  For example, the employee should be able to perform all of the following
						  actions without straying into the minimum approach distance:
* adjust his or her hardhat,
* maneuver a tool onto an energized part with a
						  reasonable amount of overreaching or underreaching,
* reach for and handle tools, material, and equipment
						  passed to him or her, and
* adjust tools, and replace components on them, when
						  necessary during the work procedure.
The training of qualified employees required under
						  Section 2940(c), and the
						  job planning and briefing required under Sections
						  3203(a) and
						  2940(e) shall
						  address selection of a proper working position.
Click
						  here to view image
Figure 1 - Maintaining the Minimum Approach
						  Distance
E.
Miscellaneous correction factors.
Changes in the air medium that forms the insulation influences the strength of
						  an air gap. A brief discussion of each factor follows.
1.
Dielectric strength of air.
The
						  dielectric strength of air in a uniform electric field at standard atmospheric
						  conditions is approximately 3 kilovolts per millimeter. [FN6]
The pressure, temperature, and humidity of the air, the
						  shape, dimensions, and separation of the electrodes, and the characteristics of
						  the applied voltage (wave shape) affect the disruptive gradient.
2.
Atmospheric effect.
The empirically
						  determined electrical strength of a given gap is normally applicable at
						  standard atmospheric conditions (20 °C, 101.3 kilopascals, 11 grams/cubic
						  centimeter humidity). An increase in the density (humidity) of the air inhibits
						  sparkover for a given air gap. The combination of temperature and air pressure
						  that results in the lowest gap sparkover voltage is high temperature and low
						  pressure. This combination of conditions is not likely to occur. Low air
						  pressure, generally associated with high humidity, causes increased electrical
						  strength. An average air pressure generally correlates with low humidity. Hot
						  and dry working conditions normally result in reduced electrical strength. The
						  equations for minimum approach distances in Table 2940.2-1 assume standard
						  atmospheric conditions.
3.
Altitude.
The reduced air pressure
						  at high altitudes causes a reduction in the electrical strength of an air gap.
						  An employer shall increase the minimum approach distance by about 3 percent per
						  300 meters (1,000 feet) of increased altitude for altitudes above 900 meters
						  (3,000 feet). Table 2940.2-7 specifies the altitude correction factor that the
						  employer shall use in calculating minimum approach distances.
IV. Determining Minimum Approach
						  Distances
A.
Factors Affecting Voltage Stress at the
						  Worksite
1.
System voltage (nominal).
The
						  nominal system voltage range determines the voltage for purposes of calculating
						  minimum approach distances. The employer selects the range in which the nominal
						  system voltage falls, as given in the relevant table, and uses the highest
						  value within that range in per unit calculations.
2.
Transient overvoltages.
Operation
						  of switches or circuit breakers, a fault on a line or circuit or on an adjacent
						  circuit, and similar activities may generate transient overvoltages on an
						  electrical system. Each overvoltage has an associated transient voltage wave
						  shape. The wave shape arriving at the site and its magnitude vary
						  considerably.
In developing requirements for minimum approach
						  distances, US Department of Labor, Occupational Safety and Health
						  Administration considered the most common wave shapes and the magnitude of
						  transient overvoltages found on electric power generation, transmission, and
						  distribution systems. The equations in Table 2940.2-1 for minimum approach
						  distances use per-unit maximum transient overvoltages, which are relative to
						  the nominal maximum voltage of the system. For example, a maximum transient
						  overvoltage value of 3.0 per unit indicates that the highest transient
						  overvoltage is 3.0 times the nominal maximum system voltage.
3.
Typical magnitude of overvoltages.
Table 5 lists the magnitude of typical transient overvoltages.
TABLE 5-MAGNITUDE OF
									 TYPICAL TRANSIENT OVERVOLTAGES
Cause
Magnitude
								  (per unit)
Energized 200-mile line without closing
								  resistors
3.5
Energized 200-mile line with one-step closing
								  resistor
2.1
Energized 200-mile line with multistep
								  resistor
2.5
Reclosing with trapped charge
								  one-step
2.2
Opening surge with single
								  restrike
3.0
Fault initiation unfaulted phase
2.1
Fault initiation adjacent
								  circuit
2.5
Fault clearing
1.7 to 1.9
4.
Standard deviation-air-gap
						  withstand.
For each air gap length under the same atmospheric
						  conditions, there is a statistical variation in the breakdown voltage. The
						  probability of breakdown against voltage has a normal (Gaussian) distribution.
						  The standard deviation of this distribution varies with the wave shape, gap
						  geometry, and atmospheric conditions. The withstand voltage of the air gap is
						  three standard deviations (3s) below the critical sparkover voltage. (The
						  critical sparkover voltage is the crest value of the impulse wave that, under
						  specified conditions, causes sparkover 50 percent of the time. An impulse wave
						  of three standard deviations below this value, that is, the withstand voltage,
						  has a probability of sparkover of approximately 1 in 1,000.)
5.
Broken Insulators.
Tests show
						  reductions in the insulation strength of insulator strings with broken skirts.
						  Broken units may lose up to 70 percent of their withstand capacity. Because an
						  employer cannot determine the insulating capability of a broken unit without
						  testing it, the employer shall consider damaged units in an insulator to have
						  no insulating value. Additionally, the presence of a live-line tool alongside
						  an insulator string with broken units may further reduce the overall insulating
						  strength. The number of good units that shall be present in a string for it to
						  be "insulated" as defined by Section
						  2700 depends on the maximum
						  overvoltage possible at the worksite.
B.
Minimum Approach Distances Based on Known,
						  Maximum-Anticipated Per-Unit Transient Overvoltages
1.
Determining the minimum approach distance
						  for AC systems.
Under Section
						  2940.2(a)(1), the
						  employer shall determine the maximum anticipated per-unit transient
						  overvoltage, phase-to-ground, through an engineering analysis or shall assume a
						  maximum anticipated per-unit transient overvoltage, phase-to-ground, in
						  accordance with Table 2940.2-5. When the employer conducts an engineering
						  analysis of the system and determines that the maximum transient overvoltage is
						  lower than specified by Table 2940.2-5, the employer must ensure that any
						  conditions assumed in the analysis, for example, that employees block reclosing
						  on a circuit or install portable protective gaps, are present during energized
						  work. To ensure that these conditions are present, the employer may need to
						  institute new livework procedures reflecting the conditions and limitations set
						  by the engineering analysis.
2.
Calculation of reduced approach distance
						  values.
An employer may take the following steps to reduce minimum
						  approach distances when the maximum transient overvoltage on the system (that
						  is, the maximum transient overvoltage without additional steps to control
						  overvoltages) produces unacceptably large minimum approach distances:
Step 1. Determine the maximum voltage (with respect to
						  a given nominal voltage range) for the energized part.
Step 2. Determine the technique to use to control the
						  maximum transient overvoltage. (See Sections IV.C and IV.D of this appendix.)
						  Determine the maximum transient overvoltage that can exist at the worksite with
						  that form of control in place and with a confidence level of 3s. This voltage
						  is the withstand voltage for the purpose of calculating the appropriate minimum
						  approach distance.
Step 3. Direct employees to implement procedures to
						  ensure that the control technique is in effect during the course of the
						  work.
Step 4. Using the new value of transient overvoltage in
						  per unit, calculate the required minimum approach distance from Table
						  2940.2-1.
C.
Methods of Controlling Possible Transient
						  Overvoltage Stress Found on a System
1.
Introduction.
There are several
						  means of controlling overvoltages that occur on transmission systems. For
						  example, the employer can modify the operation of circuit breakers or other
						  switching devices to reduce switching transient overvoltages. Alternatively,
						  the employer can hold the overvoltage to an acceptable level by installing
						  surge arresters or portable protective gaps on the system. In addition, the
						  employer can change the transmission system to minimize the effect of switching
						  operations. Section
						  4.8 of IEEE Std 516-2009 describes
						  various ways of controlling, and thereby reducing, maximum transient
						  overvoltages.
2.
Operation of circuit breakers
.
						  [FN7] The maximum transient overvoltage that can reach the worksite is often
						  the result of switching on the line on which employees are working. Disabling
						  automatic reclosing during energized line work, so that the line will not be
						  reenergized after being opened for any reason, limits the maximum switching
						  surge overvoltage to the larger of the opening surge or the greatest possible
						  fault-generated surge, provided that the devices (for example, insertion
						  resistors) are operable and will function to limit the transient overvoltage
						  and that circuit breaker restrikes do not occur. The employer shall ensure the
						  proper functioning of insertion resistors and other overvoltage-limiting
						  devices when the employer's engineering analysis assumes their proper operation
						  to limit the overvoltage level. If the employer cannot disable the reclosing
						  feature (because of system operating conditions), other methods of controlling
						  the switching surge level may be necessary.
Transient surges on an adjacent line, particularly for
						  double circuit construction, may cause a significant overvoltage on the line on
						  which employees are working. The employer's engineering analysis shall account
						  for coupling to adjacent lines.
3.
Surge arresters.
The use of modern
						  surge arresters allows a reduction in the basic impulse-insulation levels of
						  much transmission system equipment. The primary function of early arresters was
						  to protect the system insulation from the effects of lightning. Modern
						  arresters not only dissipate lightning-caused transients, but may also control
						  many other system transients caused by switching or faults.
The employer may use properly designed arresters to
						  control transient overvoltages along a transmission line and thereby reduce the
						  requisite length of the insulator string and possibly the maximum transient
						  overvoltage on the line. [FN8]
4.
Switching Restrictions.
Another
						  form of overvoltage control involves establishing switching restrictions,
						  whereby the employer prohibits the operation of circuit breakers until certain
						  system conditions are present. The employer restricts switching by using a
						  tagging system, similar to that used for a permit, except that the common term
						  used for this activity is a "hold-off" or "restriction." These terms indicate
						  that the restriction does not prevent operation, but only modifies the
						  operation during the livework activity.
D.
Minimum Approach Distance Based on Control
						  of Maximum Transient Overvoltage at the Worksite
When the employer institutes control of maximum
						  transient overvoltage at the worksite by installing portable protective gaps,
						  the employer may calculate the minimum approach distance as follows:
Step 1. Select the appropriate withstand voltage for
						  the protective gap based on system requirements and an acceptable probability
						  of gap sparkover. [FN9]
Step 2. Determine a gap distance that provides a
						  withstand voltage [FN10] greater than or equal to the one selected in the first
						  step. [FN11]
Step 3. Use 110 percent of the gap's critical sparkover
						  voltage to determine the phase-to-ground peak voltage at gap sparkover (VPPG
						  Peak).
Step 4. Determine the maximum transient overvoltage,
						  phase-to-ground, at the worksite from the following formula:
Click
						  here to view image
Step 5. Use this value of T [FN12] in the equation in
						  Table 2940.2-1 to obtain the minimum approach distance. If the worksite is no
						  more than 900 meters (3,000 feet) above sea level, the employer may use this
						  value of T to determine the minimum approach distance from Table 14 through
						  Table 21.
NOTE All rounding shall be to the next higher value
						  (that is, always round up).
Sample protective gap calculations.
Problem: Employees are to perform work on a
						  500-kilovolt transmission line at sea level that is subject to transient
						  overvoltages of 2.4 p.u. The maximum operating voltage of the line is 550
						  kilovolts. Determine the length of the protective gap that will provide the
						  minimum practical safe approach distance. Also, determine what that minimum
						  approach distance is:
Step 1. Calculate the smallest practical maximum
						  transient overvoltage (1.25 times the crest phase-to-ground voltage).
						  [FN13]
Click
						  here to view image
This value equals the withstand voltage of the
						  protective gap.
Step 2. Using test data for a particular protective
						  gap, select a gap that has a critical sparkover voltage greater than or equal
						  to:
561kV / 0.85 = 660kV
For example, if a protective gap with a 1.22-m
						  (4.0-foot) spacing tested to a critical sparkover voltage of 665 kilovolts
						  (crest), select this gap spacing.
Step 3. The phase-to-ground peak voltage at gap
						  sparkover (VPPG Peak) is 110 percent of the value from the previous
						  step:
665kV / 1.10 = 732kV
This value corresponds to the withstand voltage of the
						  electrical component of the minimum approach distance.
Step 4. Use this voltage to determine the worksite
						  value of T:
T = 732/564 = 1.7
p.u.
Step 5. Use this value of T in the equation in Table
						  2940.2-1 to obtain the minimum approach distance, or look up the minimum
						  approach distance in Table 14 through Table 21:
MAD = 2.29m (7.6 ft).
E.
Location of Protective Gaps
1.
Adjacent structures.
The employer
						  may install the protective gap on a structure adjacent to the worksite, as this
						  practice does not significantly reduce the protection afforded by the
						  gap.
2.
Terminal stations.
Gaps installed
						  at terminal stations of lines or circuits provide a level of protection;
						  however, that level of protection shall not extend throughout the length of the
						  line to the worksite. The use of substation terminal gaps raises the
						  possibility that separate surges could enter the line at opposite ends, each
						  with low enough magnitude to pass the terminal gaps without sparkover. When
						  voltage surges occur simultaneously at each end of a line and travel toward
						  each other, the total voltage on the line at the point where they meet is the
						  arithmetic sum of the two surges. A gap installed within 0.8 km (0.5 mile) of
						  the worksite will protect against such intersecting waves. Engineering studies
						  of a particular line or system may indicate that employers can adequately
						  protect employees by installing gaps at even more distant locations. In any
						  event, unless using the default values for T from Table 2940.2-5, the employer
						  shall determine T at the worksite.
3.
Worksite.
If the employer installs
						  protective gaps at the worksite, the gap setting establishes the worksite
						  impulse insulation strength. Lightning strikes as far as 6 miles from the
						  worksite can 1cause a voltage surge greater than the gap withstand voltage, and
						  a gap sparkover can occur. In addition, the gap can sparkover from overvoltages
						  on the line that exceed the withstand voltage of the gap. Consequently, the
						  employer shall protect employees from hazards resulting from any sparkover that
						  could occur.
F.
Disabling automatic reclosing.
There are two reasons to disable the automatic-reclosing feature of
						  circuit-interrupting devices while employees are performing live-line
						  work:
* To prevent reenergization of a circuit faulted during
						  the work, which could create a hazard or result in more serious injuries or
						  damage than the injuries or damage produced by the original fault;
* To prevent any transient overvoltage caused by the
						  switching surge that would result if the circuit were reenergized. However, due
						  to system stability considerations, it may not always be feasible to disable
						  the automatic-reclosing feature.
V. Minimum Approach--Distance
						  Tables
A.
Alternative minimum approach
						  distances
. Employers may use the minimum approach distances in Table 6
						  through Table 13 provided that the employer follows the notes to those
						  tables.
TABLE 6--AC MINIMUM APPROACH DISTANCES--72.6 TO
						  121.0 KV
Phase-to-ground
									 exposure
Phase-to-phase
									 exposure
T
									 (p.u.)
m
ft
m
ft
1.5
0.67
2.2
0.84
2.8
1.6
0.69
2.3
0.87
2.9
1.7
0.71
2.3
0.90
3.0
1.8
0.74
2.4
0.93
3.1
1.9
0.76
2.5
0.96
3.1
2.0
0.78
2.6
0.99
3.2
2.1
0.81
2.7
1.01
3.3
2.2
0.83
2.7
1.04
3.4
2.3
0.85
2.8
1.07
3.5
2.4
0.88
2.9
1.10
3.6
2.5
0.90
3.0
1.13
3.7
2.6
0.92
3.0
1.16
3.8
2.7
0.95
3.1
1.19
3.9
2.8
0.97
3.2
1.22
4.0
2.9
0.99
3.2
1.24
4.1
3.0
1.02
3.3
1.27
4.2
3.1
1.04
3.4
1.30
4.3
3.2
1.06
3.5
1.33
4.4
3.3
1.09
3.6
1.36
4.5
3.4
1.11
3.6
1.39
4.6
3.5
1.13
3.7
1.42
4.7
TABLE 7--AC MINIMUM APPROACH DISTANCES--121.1 TO
						  145.0 KV
Phase-to-ground
									 exposure
Phase-to-phase
									 exposure
T
									 (p.u.)
m
ft
m
ft
1.5
0.74
2.4
0.95
3.1
1.6
0.76
2.5
0.98
3.2
1.7
0.79
2.6
1.02
3.3
1.8
0.82
2.7
1.05
3.4
1.9
0.85
2.8
1.08
3.5
2.0
0.88
2.9
1.12
3.7
2.1
0.90
3.0
1.15
3.8
2.2
0.93
3.1
1.19
3.9
2.3
0.96
3.1
1.22
4.0
2.4
0.99
3.2
1.26
4.1
2.5
1.02
3.3
1.29
4.2
2.6
1.04
3.4
1.33
4.4
2.7
1.07
3.5
1.36
4.5
2.8
1.10
3.6
1.39
4.6
2.9
1.13
3.7
1.43
4.7
3.0
1.16
3.8
1.46
4.8
3.1
1.19
3.9
1.50
4.9
3.2
1.21
4.0
1.53
5.0
3.3
1.24
4.1
1.57
5.2
3.4
1.27
4.2
1.60
5.2
3.5
1.30
4.3
1.64
5.4
TABLE 8--AC MINIMUM APPROACH DISTANCES--145.1 TO
						  169.0 KV
Phase-to-ground
									 exposure
Phase-to-phase
									 exposure
T
									 (p.u.)
m
ft
m
ft
1.5
0.81
2.7
1.05
3.4
1.6
0.84
2.8
1.09
3.6
1.7
0.87
2.9
1.13
3.7
1.8
0.90
3.0
1.17
3.8
1.9
0.94
3.1
1.21
4.0
2.0
0.97
3.2
1.25
4.1
2.1
1.00
3.3
1.29
4.2
2.2
1.03
3.4
1.33
4.4
2.3
1.07
3.5
1.37
4.5
2.4
1.10
3.6
1.41
4.6
2.5
1.13
3.7
1.45
4.8
2.6
1.17
3.8
1.49
4.9
2.7
1.20
3.9
1.53
5.0
2.8
1.23
4.0
1.57
5.2
2.9
1.26
4.1
1.61
5.3
3.0
1.30
4.3
1.65
5.4
3.1
1.33
4.4
1.70
5.6
3.2
1.36
4.5
1.76
5.8
3.3
1.39
4.6
1.82
6.0
3.4
1.43
4.7
1.88
6.2
3.5
1.46
4.8
1.94
6.4
TABLE 9--AC MINIMUM APPROACH DISTANCES--169.1 TO
						  242.0 KV
Phase-to-ground
									 exposure
Phase-to-phase
									 exposure
T
									 (p.u.)
m
ft
m
ft
1.5
1.02
3.3
1.37
4.5
1.6
1.06
3.5
1.43
4.7
1.7
1.11
3.6
1.48
4.9
1.8
1.16
3.8
1.54
5.1
1.9
1.21
4.0
1.60
5.2
2.0
1.25
4.1
1.66
5.4
2.1
1.30
4.3
1.73
5.7
2.2
1.35
4.4
1.81
5.9
2.3
1.39
4.6
1.90
6.2
2.4
1.44
4.7
1.99
6.5
2.5
1.49
4.9
2.08
6.8
2.6
1.53
5.0
2.17
7.1
2.7
1.58
5.2
2.26
7.4
2.8
1.63
5.3
2.36
7.7
2.9
1.67
5.5
2.45
8.0
3.0
1.72
5.6
2.55
8.4
3.1
1.77
5.8
2.65
8.7
3.2
1.81
5.9
2.76
9.1
3.3
1.88
6.2
2.86
9.4
3.4
1.95
6.4
2.97
9.7
3.5
2.01
6.6
3.08
10.1
TABLE 10--AC MINIMUM APPROACH DISTANCES--242.1 TO
						  362.0 KV
Phase-to-ground
									 exposure
Phase-to-phase
									 exposure
T (p.u.)
m
ft
m
ft
1.5
1.37
4.5
1.99
6.5
1.6
1.44
4.7
2.13
7.0
1.7
1.51
5.0
2.27
7.4
1.8
1.58
5.2
2.41
7.9
1.9
1.65
5.4
2.56
8.4
2.0
1.72
5.6
2.71
8.9
2.1
1.79
5.9
2.87
9.4
2.2
1.87
6.1
3.03
9.9
2.3
1.97
6.5
3.20
10.5
2.4
2.08
6.8
3.37
11.1
2.5
2.19
7.2
3.55
11.6
2.6
2.29
7.5
3.73
12.2
2.7
2.41
7.9
3.91
12.8
2.8
2.52
8.3
4.10
13.5
2.9
2.64
8.7
4.29
14.1
3.0
2.76
9.1
4.49
14.7
3.1
2.88
9.4
4.69
15.4
3.2
3.01
9.9
4.90
16.1
3.3
3.14
10.3
5.11
16.8
3.4
3.27
10.7
5.32
17.5
3.5
3.41
11.2
5.52
18.1
TABLE 11--AC MINIMUM APPROACH DISTANCES--362.1 TO
						  420.0 KV
Phase-to-ground
									 exposure
Phase-to-phase exposure
T
									 (p.u.)
m
ft
m
ft
1.5
1.53
5.0
2.40
7.9
1.6
1.62
5.3
2.58
8.5
1.7
1.70
5.6
2.75
9.0
1.8
1.78
5.8
2.94
9.6
1.9
1.88
6.2
3.13
10.3
2.0
1.99
6.5
3.33
10.9
2.1
2.12
7.0
3.53
11.6
2.2
2.24
7.3
3.74
12.3
2.3
2.37
7.8
3.95
13.0
2.4
2.50
8.2
4.17
13.7
2.5
2.64
8.7
4.40
14.4
2.6
2.78
9.1
4.63
15.2
2.7
2.93
9.6
4.87
16.0
2.8
3.07
10.1
5.11
16.8
2.9
3.23
10.6
5.36
17.6
3.0
3.38
11.1
5.59
18.3
3.1
3.55
11.6
5.82
19.1
3.2
3.72
12.2
6.07
19.9
3.3
3.89
12.8
6.31
20.7
3.4
4.07
13.4
6.56
21.5
3.5
4.25
13.9
6.81
22.3
TABLE 12--AC MINIMUM APPROACH DISTANCES--420.1 TO
						  550.0 KV
Phase-to-ground
									 exposure
Phase-to-phase
									 exposure
T
									 (p.u.)
m
ft
m
ft
1.5
1.95
6.4
3.46
11.4
1.6
2.11
6.9
3.73
12.2
1.7
2.28
7.5
4.02
13.2
1.8
2.45
8.0
4.31
14.1
1.9
2.62
8.6
4.61
15.1
2.0
2.81
9.2
4.92
16.1
2.1
3.00
9.8
5.25
17.2
2.2
3.20
10.5
5.55
18.2
2.3
3.40
11.2
5.86
19.2
2.4
3.62
11.9
6.18
20.3
2.5
3.84
12.6
6.50
21.3
2.6
4.07
13.4
6.83
22.4
2.7
4.31
14.1
7.18
23.6
2.8
4.56
15.0
7.52
24.7
2.9
4.81
15.8
7.88
25.9
3.0
5.07
16.6
8.24
27.0
TABLE 13--AC MINIMUM APPROACH DISTANCES--550.1 TO
						  800.0 KV
Phase-to-ground
									 exposure
Phase-to-phase
									 exposure
T
									 (p.u.)
m
ft
m
ft
1.5
3.16
10.4
5.97
19.6
1.6
3.46
11.4
6.43
21.1
1.7
3.78
12.4
6.92
22.7
1.8
4.12
13.5
7.42
24.3
1.9
4.47
14.7
7.93
26.0
2.0
4.83
15.8
8.47
27.8
2.1
5.21
17.1
9.02
29.6
2.2
5.61
18.4
9.58
31.4
2.3
6.02
19.8
10.16
33.3
2.4
6.44
21.1
10.76
35.3
2.5
6.88
22.6
11.38
37.3
Notes to Table 6 through Table 13:
1. The employer must determine the maximum anticipated
						  per-unit transient overvoltage, phase-to-ground, through an engineering
						  analysis, as required by Section
						  2940.2(a)(1)(A),
						  or assume a maximum anticipated per-unit transient overvoltage,
						  phase-to-ground, in accordance with Table 2940.2-5.
2. For phase-to-phase exposures, the employer must
						  demonstrate that no insulated tool spans the gap and that no large conductive
						  object is in the gap.
3. The worksite must be at an elevation of 900 meters
						  (3,000 feet) or less above sea level.[FN1]
Federal, State, and local regulatory bodies and
						  electric utilities set reliability requirements that limit the number and
						  duration of system outages.[FN2]
. Sparkover is a disruptive electric discharge in which
						  an electric arc forms and electric current passes through air.[FN3]
. The withstand voltage is the voltage at which
						  sparkover is not likely to occur across a specified distance. It is the voltage
						  taken at the 3s point below the sparkover voltage, assuming that the sparkover
						  curve follows a normal distribution.[FN4]
Test data demonstrates that the saturation factor is
						  greater than 0 at peak voltages of about 630 kilovolts. Systems operating at
						  345 kilovolts (or maximum system voltages of 362 kilovolts) can have peak
						  maximum transient overvoltages exceeding 630 kilovolts. Table 2940.2-1 sets
						  equations for calculating a based on peak voltage.[FN5]
For voltages of 50 to 300 volts, Table 2940.2-1
						  specifies a minimum approach distance of "avoid contact." The minimum approach
						  distance for this voltage range contains neither an electrical component nor an
						  ergonomic component.[FN6]
For the purposes of estimating arc length, Title 8,
						  Subchapter 5, Group 2, generally assumes a more conservative dielectric
						  strength of 10 kilovolts per 25.4 millimeters, consistent with assumptions made
						  in consensus standards such as the National Electrical Safety Code (IEEE
						  C2-2012). The more conservative value accounts for variables such as electrode
						  shape, wave shape, and a certain amount of overvoltage.[FN7]
The detailed design of a circuit interrupter, such as
						  the design of the contacts, resistor insertion, and breaker timing control, are
						  beyond the scope of this appendix. The design of the system generally accounts
						  for these features. This appendix only discusses features that can limit the
						  maximum switching transient overvoltage on a system.[FN8]
Surge arrester application is beyond the scope of this
						  appendix. However, if the employer installs the arrester near the work site,
						  the application would be similar to the protective gaps discussed in paragraph
						  IV.D of this appendix.[FN9]
The employer should check the withstand voltage to
						  ensure that it results in a probability of gap flashover that is acceptable
						  from a system outage perspective. (In other words, a gap sparkover will produce
						  a system outage. The employer should determine whether such an outage will
						  impact overall system performance to an acceptable degree.) In general, the
						  withstand voltage should be at least 1.25 times the maximum crest operating
						  voltage.[FN10]
The manufacturer of the gap provides, based on test
						  data, the critical sparkover voltage for each gap spacing (for example, a
						  critical sparkover voltage of 665 kilovolts for a gap spacing of 1.2 meters).
						  The withstand voltage for the gap is equal to 85 percent of its critical
						  sparkover voltage.[FN11]
Switch steps 1 and 2 if the length of the protective
						  gap is known.[FN12]
IEEE Std 516-2009 states that most employers add 0.2 to
						  the calculated value of T as an additional safety factor.[FN13]
To eliminate sparkovers due to minor system
						  disturbances, the employer should use a withstand voltage no lower than 1.25
						  p.u. Note that this is a practical, or operational, consideration only. It may
						  be feasible for the employer to use lower values of withstand
						  voltage.
1. New
						  Appendix A filed 2-27-2018; operative 4-1-2018 (Register 2018, No. 9). For
						  prior history, see Register 92, No. 50.
2. Amendment of Appendix
						  filed 12-5-2019; operative 4-1-2020 (Register 2019, No.
						  49).
Note: Authority cited: Section
							 142.3, Labor
							 Code. Reference: Section
							 142.3, Labor
							 Code.