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Hazardous Energy Control » Deenergizing Transmission and Distribution Lines and Equipment for Employee Protection
The "269" standard (1910.269(m)) hazardous energy control requirements for transmission and distribution (T&D) apply to all overhead, underground, and substation work by 269-qualified employees [See 1910.269(x)]. Any line, circuit, or equipment that has been shut down can only be worked on as deenergized if all of the 1910.269(m) requirements are met; if all are not met, then the work must be done as if the line, circuit, or equipment is still energized. In addition to deenergizing the equipment to be worked, grounding, as outlined in 1910.269(n), is essential for worker safety.
Deenergizing a System
Many utilities have developed specific switching procedures for specific deenergization tasks. These procedures are typically very detailed, including the confirmation and verification of commands received via radio to crews at remote locations. Most utilities have a center from which all transmission and distribution operations are controlled by what OSHA calls a "system operator." Before beginning work, and as part of the job briefing, the person in charge at the work site must review the isolation steps with all workers that will be doing the work. [See Hazard Assessment and Job Briefing] When field workers need to deenergize T&D lines or equipment for work in which a system operator is in charge, 1910.269(m) requires that the following sequence be followed:
|The field worker designated to be in charge of clearance formally requests that the system operator deenergize the particular lines or equipment.
|All possible source connections through which energy could flow (including backfeed) are identified by a 269-qualified person, opened/operated in a proper sequence, rendered inoperable, and tagged [LOTO Generation] by the system operator. (This step is sometimes referred to as development of a "switching order.")
|The system operator directs field personnel to lock in the open position (such as locking the handle for a pole-mounted, gang-operated load break switch) or otherwise render inoperable (such as removing a switch handle) any switching device that could be accessed by anyone not under that employer's control – such as the general public.
|The system operator disables and tags automatic devices, such as reclosers and sectionalizers, and sets remote-controlled switching devices to local control and tags them. (See Disabling Reclosers and Remotely Operated Devices.)
|After completing all of the above steps the system operator notifies the person in charge, and the lines and equipment to be worked on must be properly tested by field personnel to ensure they are deenergized.
|Protective grounds must then be installed in the appropriate sequence and as otherwise required by 1910.269(n). (See Grounding for Employee Protection.)
Only when all of the above steps are completed may the lines or equipment be worked on as deenergized.
Some of the above steps may be omitted in certain situations, including:
|there is no system operator, or if procedures allow work to be done without the system operator's involvement
|the first step above can be omitted, and the person in charge at the work site is responsible for completing the remaining steps.
|the isolating device is at the work location, the crew working on the lines can control its operation, and the means of disconnection is accessible and visible to and under the sole control of the employee in charge of the clearance
|tags do not need to be installed.
|distribution systems (for example, in many large cities) have a secondary network that is fed by a number of transformers with primary switches and automatic reverse-current trip breakers (called network protectors)
|OSHA considers it a de minimis violation of 1910.269(m)(3)(ii) if, during work on the primary feeder, the network protectors are not tagged to their associated network transformers, as long as, among other things, the primary feeder is tested to prove that it is deenergized, grounds are installed, protectors are maintained to open on backfeed, protectors are inhibited from manual closing, and procedures allow manual closing of protectors only when the feeder is energized. See Compliance Directive CPL 02-01-038, Appendix B, Item 10.
Releasing and Reenergizing a System
When deenergized work has been completed, the person in charge must:
Tell all workers that the clearance is going to be released and the equipment can no longer be considered deenergized.
Ensure that workers are clear and will remain clear of the equipment.
Have protective grounds removed before the clearance is released and the equipment turned back to the system operator for reenergizing. (See Grounding for Employee Protection for requirements such as attaching and removing grounds.)
Tags can then be removed and the equipment energized.