Source: https://app.leg.wa.gov/WAC/default.aspx?cite=296-45-902
Timestamp: 2020-08-09 14:54:00
Document Index: 301679469

Matched Legal Cases: ['§ 1910', '§ 1910', '§ 1910', '§ 1910', '§ 1910', '§ 296', '§ 296']

WAC 296-45-902:
WACs > Title 296 > Chapter 296-45 > Section 296-45-902
296-45-900 << 296-45-902 >> 296-45-903
PDFWAC 296-45-902
Appendix A—Working on exposed energized parts—Nonmandatory.
This appendix is identical to 29 C.F.R. 1910.269 Appendix B, Working on Exposed Energized Parts. However, all references to live-line barehand work have been deleted since it is prohibited in Washington state.
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 criteria1 and to withstand the maximum overvoltage's 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 § 1910.269(l)(3). Employers must use the technical criteria and methodology presented in this appendix in establishing minimum approach distances in accordance with § 1910.269(l)(3)(i) and Table R-3 and Table R-8. 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 overvoltage's specified in Table R-9 for voltages over 72.5 kilovolts, the employer must 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.
Note to the definition of guarded: Wires that are insulated, but not otherwise protected, are not guarded.
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.
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 must avoid contact with the exposed parts, and the protective equipment used (such as rubber insulating gloves) must provide insulation for the voltages involved.
Normal system design may provide or include a means (such as lightning arrestors) to control maximum anticipated transient overvoltage's, or the employer may use temporary devices (portable protective gaps) or measures (such as preventing automatic circuit breaker reclosing) to achieve the same result. Paragraph (l)(3)(ii) of § 1910.269 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 R-9, which specifies the following maximums for ac systems:
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 with respect to an energized part, when the employee is at ground potential.
Sparkover Distance for Rod-to-rod Gap
60 Hz Rod-to-Rod sparkover (kV peak)
53 . . . .
95 . . . .
104 . . . .
112 . . . .
120 . . . .
143 . . . .
167 . . . .
192 . . . .
218 . . . .
243 . . . .
270 . . . .
322 . . . .
Calculating the Electrical Component Of MAD 751 V To 72.5 KV
Maximum system phase-to-phase voltage (kV)
1. Divide by √3 . . . .
2. Multiply by √2 . . . .
3. Multiply by 3.0 . . . .
4. Divide by 0.85 . . . .
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) . . . .
Equation 1 - For voltages of 72.6 kV to 800 kV
a = A factor relating to the saturation of air at system voltages of 345 kilovolts or higher;4
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
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 must 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.
Equations for Calculating the Surge Factor, a
VPeak = TL-GVL-G√2 . . . .
635 kV or less 0
635.1 to 915 kV
(VPeak- 635)/140,000
915.1 to 1,050 kV (VPeak-645)/135,000
VPeak= TL-GVL-G√2 . . . .
More than 1,050 kV
(VPeak-675)/125,000
VPeak = (1.35TL-G + 0.45)VL-G√2 . . . .
630 kV or less 0
630.1 to 848 kV (VPeak-630)/155,000
848.1 to 1,131 kV (VPeak-633.6)/152,207
1,131.1 to 1,485 kV (VPeak-628)/153,846
More than 1,485 kV (VPeak-350.5)/203,666
1Use 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.
Ergonomic Component of Minimum Approach Distance
0.301 to 0.750 . . . .
0.751 to 72.5 . . . .
72.6 to 800 . . . .
The employer must add this distance to the electrical component of the minimum approach distance to obtain the full 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.
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 R-3 assume standard atmospheric conditions.
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.
Magnitude of Typical Transient Overvoltages
Magnitude (per unit)
Energized 200-mile line without closing resistors . . . .
Energized 200-mile line with one-step closing resistor . . . .
Energized 200-mile line with multistep resistor . . . .
Reclosing with trapped charge one-step resistor . . . .
Opening surge with single restrike . . . .
Fault initiation unfaulted phase . . . .
Fault initiation adjacent circuit . . . .
Fault clearing . . . .
B. Minimum Approach Distances Based on Known, Maximum-Anticipated Per-Unit Transient Overvoltages.
C. Methods of Controlling Possible Transient Overvoltage Stress Found on a System.
D. Minimum Approach Distance Based on Control of Maximum Transient Overvoltage at the Worksite.
Step 2. Determine a gap distance that provides a withstand voltage10 greater than or equal to the one selected in the first step.11
All rounding must be to the next higher value (that is, always round up).
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):13
MAD = 2.29 m (7.6 ft).
E. Location of Protective Gaps.
• 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.
Tables 6 through 13 have been deleted. They became obsolete on April 1, 2015. Employers may use the minimum approach distances in Table 14 through Table 21 provided that the employer follows the notes to those tables.
AC Minimum Approach Distances-72.6 to 121.0 KV
T (p.u.)
1.5 . . . .
1.6 . . . .
1.7 . . . .
1.9 . . . .
2.0 . . . .
2.1 . . . .
2.2 . . . .
2.3 . . . .
2.4 . . . .
2.5 . . . .
2.6 . . . .
2.8 . . . .
2.9 . . . .
3.1 . . . .
3.2 . . . .
3.3 . . . .
3.4 . . . .
3.5 . . . .
AC Minimum Approach Distances-121.1 to 145.0 KV
AC Minimum Approach Distances-145.1 to 169.0 KV
AC Minimum Approach Distances-169.1 to 242.0 KV
AC Minimum Approach Distances-242.1 to 362.0 KV
AC Minimum Approach Distances-362.1 to 420.0 KV
AC Minimum Approach Distances-420.1 to 550.0 KV
AC Minimum Approach Distances-550.1 to 800.0 KV
1. The employer must determine the maximum anticipated per-unit transient overvoltage, phase-to-ground, through an engineering analysis, as required by § 1910.269(l)(3)(ii), or assume a maximum anticipated per-unit transient overvoltage, phase-to-ground, in accordance with Table R-9.
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.
1Federal, state, and local regulatory bodies and electric utilities set reliability requirements that limit the number and duration of system outages.
2Sparkover is a disruptive electric discharge in which an electric arc forms and electric current passes through air.
3The 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.
4Test 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 R-3 sets equations for calculating a based on peak voltage.
5For voltages of 50 to 300 volts, Table R-3 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.
6For the purposes of estimating arc length, § 1910.269 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.
7The 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.
8Surge arrester application is beyond the scope of this appendix. However, if the employer installs the arrester near the worksite, the application would be similar to the protective gaps discussed in paragraph IV.D of this appendix.
9The 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.
10The 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.
11Switch steps 1 and 2 if the length of the protective gap is known.
12IEEE Std 516-2009 states that most employers add 0.2 to the calculated value of T as an additional safety factor.
13To 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.
[Statutory Authority: RCW 49.17.010, 49.17.040, 49.17.050, 49.17.060 and chapter 49.17 RCW. WSR 19-13-083, § 296-45-902, filed 6/18/19, effective 8/1/19; WSR 16-10-082, § 296-45-902, filed 5/3/16, effective 7/1/16.]