Washington Administrative Code › Title 296 - Labor and Industries, Department of › Chapter 296-45 - Electric power generation, transmission, and distribution › Section 296-45-902 - Appendix A-Working on exposed energized parts-Nonmandatory

Current through Register Vol. 24-14, July 15, 2024
Note:
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.
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
				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.
II.
General
A.
Definitions
. The
			 following definitions from § 1910.269(x) 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, fenced, enclosed, or
				otherwise protected, by means of suitable covers or casings, barrier rails or
				screens, mats, or platforms, designed to minimize the possibility, under normal
				conditions, of dangerous approach or inadvertent 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
. 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 must
			 avoid contact with the exposed parts, and the protective equipment used (such
			 as rubber insulating gloves) must provide insulation for the voltages
			 involved.
C.
Exposed
			 energized parts over 300 volts AC
. Paragraph (l)(3)(i) of §
			 1910.269 requires the employer to establish minimum approach distances no less
			 than the distances computed by Table R-3 for AC systems so that employees can
			 work safely without risk of sparkover.2
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 must 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 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:
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 paragraph 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 with respect to an energized
			 part, when the employee is at ground potential.