Voice of Experience: Saved by the Bond
In this edition of “Voice of Experience,” we’re going to examine a recent incident that helps to illustrate the point that when workers follow the rules of OSHA 29 CFR 1910.269(n), “Grounding for the protection of employees,” it can save lives.
A transmission crew was assigned the task of transferring conductor and guys on the inside phase of a 115-kV three-pole angle. The pole had been set by another crew and was ready for the transfer; the three-pole-angle structure was sitting in a swampy area not accessible by trucks that day. The crew went in on a Marsh Master with tools to work on the structure.
A clearance had been arranged by the crew leader to de-energize and ground the 115-kV line. The switching order was reviewed and dispatched by a system operator at the origination point of the 115-kV line, about 25 miles west of the work location. There was a three-way GOAB switch approximately 25 miles east of the work location. The system operator was to initiate the switching order at the power plant. A crew person was assigned to open the GOAB switch. Two bucket trucks were assigned to ground on either side of the three-pole-angle midspan when the line was de-energized.
The morning of the incident, the bucket trucks were in place, the crew member was ready to open the GOAB switch, the remaining crew members were at the pole in the Marsh Master, and the system operator confirmed with everyone that they were ready to start the switching order. At that time, the system operator transferred the load on the 115-kV line to another breaker and opened that breaker via SCADA. He placed a hold tag on system control. Next, the system operator went into the switch yard, checked the breaker open by mechanical indicator and placed a hold tag on the breaker handle. He then opened a motor-operated 115-kV switch to isolate the line from the station bus. The system operator checked all three blades open in the clear. He locked the switch in the open position and placed a hold tag on the switch handle. Then he pulled the pin from the motor-operated switch to isolate both the motor and switch. When that was done, the system operator had completed his part of the switching order. He reported the status to the crew leader, who was supposed to receive the clearance and was in charge of the work to be done.
The system operator then called the crew member at the GOAB switch and instructed him to open the switch, check all three blades in the clear, lock the switch handle open and place a hold tag on the switch handle in the open position. This de-energized the 115-kV line back to the substation. Once this step was completed, the operator called the crew leader and advised him that he had clearance between the open and tagged GOAB switch and the open and tagged motor-operated switch in the substation. The system operator then advised the crew leader to have two bucket trucks check for absence of voltage and install system safety grounds at the two locations on either side of the work location. The bracketed grounds were 500 to 1,000 feet apart. After the grounds were in place, the clearance was accepted by the crew leader and the task began at the work location.
The crew members assigned to do the transfer immediately climbed the pole and began their work. The first crew member placed a pole band under the work area and bonded the new pole to the grounded conductor. The crew then installed a temporary system safety ground across the deadened conductors to cut and remove the permanent jumper. This was done to allow the transfer from the old pole to the new pole. Once the down guys were installed and secured, the conductor was cut off with 15-ton chain falls and moved from the old pole to the new one. When the conductor was in place and deadened on the new pole, the crew cut the old pole out of the way and prepared to make the new permanent jumper connection.
At this point in the workday, the substation operators changed shifts and a new system operator came on shift. The outgoing and incoming operators exchanged operating information, after which the outgoing operator immediately left the premises.
The incoming system operator proceeded to the switch yard, removed the tags and locks off the breaker and switch, and reinstalled the pin in the motor. He then went back to the control room, closed the switch and then closed the breaker. The breaker operated and locked out. The system operator decided to try it again. He reset the breaker to closed, and it locked out again. At this point, the system operator called the crew leader, who was also the clearance holder, to confirm the clearance had been released. It had not been released, and at the time the system operator closed the breaker to re-energize the line, two linemen were in direct contact with the permanent jumper and were in the process of making the permanent connection.
The system operator asked the crew leader for confirmation that the clearance had been released and all employees were in clear. The crew leader informed the operator that the work was in progress and would not be completed for some time. The system operator told the crew leader that he had accidentally made the line hot – twice – and wanted to know if everyone was OK. It was later discovered that the information exchange was misunderstood by the incoming operator. Without verifying the status of the clearance, the system operator chose to make the line hot. At the very moment the 115-kV line became hot, employees were in contact with the 1245-MCM wire making up the jumper.
Those employees never knew the line was hot until the crew leader asked if they had received a shock. They never felt anything. That’s because of the law of parallel paths and equipotential work-zone bonding. The system grounds tripped the breaker, and bonding the conductor and pole together ensured that there was no current flow through the employees. The system grounds were installed midspan between structures, static wires and phases to a single system ground to a temporary ground. The ground had been megged to fewer than 100 ohms when the crew did the installation that morning. The system grounds were removed after the event, and it was discovered that all conductors had been properly brushed and cleaned before the grounds were in. There were small burn marks on the system safety ground clamps.
If an electric utility worker follows industry regulations, that worker should remain safe even if the operator who is in contact with the system fails to perform to expectations. The system grounding requirement and regulations have not changed in wording or meaning since the 1910.269 standard was first published 25 years ago. There were no changes to the wording in the 2014 update.
The industry has struggled with understanding the relationship between system grounding and work-zone bonding since the beginning. Hopefully, the preceding example will encourage greater understanding and correct application in the future.
About the Author: Danny Raines, CUSP, safety consultant, distribution and transmission, retired from Georgia Power after 40 years of service and opened Raines Utility Safety Solutions LLC, providing compliance training, risk assessments and safety observation programs. He also is an affiliate instructor at Georgia Tech Research Center OSHA Outreach in Atlanta.