The objective of this research is to identify ways to reduce SIFs.
Workshops
Workshops on SIFs are being held to exchange lessons learned on
approaches to reduce SIFs. Workshops include presentations of SIFs
and/or pSIFs (potential SIFs / near misses). Specific practices are
reviewed. Attendees brainstorm approaches to reduce SIFs, including
programs to change culture, increase awareness, change practices, and
evaluate new technologies. Attendees will develop a set of questions
that can be brought home to use as a self review for a utility.
Past Meetings
Overhead SIFs–April 4, 2023 in Charlotte, NC. See here
for results.
Underground SIFs–November 9, 2023 in San Antonio, TX, hosted by CPS Energy. See here
for results.
We are starting a library of SIFs and pSIFs. Documentation also includes
the following review questions and improvement options generated in
brainstorming sessions with utility participants.
This library is a way to exchange information on hazards with different
equipment and scenarios.
Background and Related Work
The EEI has several ongoing efforts focused on SIFs
(https://powertopreventsif.com). As part of that work, they evaluated
trends in injuries and fatalities as shown in Figure 1. While the
industry has made progress on injury rates, the most severe events have
a relatively flat trend rate. More industry work will be needed to make
an impact and improve rates of SIFs.
Figure 1:
Power generation and delivery injury and fatality trends (EEI, 2023)
Research has shown that SIFs are often caused by high energy, either
electrical, mechanical, or chemical. For distribution work, many of
these high-energy hazards are present. The goal of this research is to
focus on hazards specific to distribution work. Then, ways to reduce
risks through direct controls or other measures. The focus on this
research is practices and technologiest that can make an impact on SIFs.
Events submitted by utilities and reviewed by utility peers
This section includes summaries of SIF events or near misses presented
by utilities. Documentation also includes the following:
Review questions–These are meant for utilities to be able to review
their current practices and equipment for the scenario involved.
Improvement options–Ideas generated by participants to avoid hazards
or otherwise minimize risks.
This library is a way to exchange information on hazards with different
equipment and scenarios. If you have an event you’d like to present in a
review session, please contact Tom Short.
1.1 - 4.8-kV Arc Flash during Switching
An arc flash occurred when phases were crossed during a live switching operation
A crew was performing a live switching operation on a 4-kV E-box (a custom four-way switch–see Figure 1 through 3) to open a circuit. The switched is opened using an auxiliary oil-filled switch with load breaking capability (Figure 4). Switching is a three-person operation: two line workers hold leads on either side of blade contacts on the E-box, and an operator up top operates the switch. A normal operation is:
Line workers remove covers of the phase to be switched.
Each line worker applies and holds their lead to the ends of the switch. The switch on top is open.
The switch operator closes the switch. This shorts out the E-box and puts the switch in parallel with the E-box blades. This allows the blades to be opened without drawing an arc.
The line workers use a blade removal tool to pull their blades to open the E-box (Figure 5).
The switch operator up top opens the switch to disconnect the circuit.
The line workers lift their leads, re-install the covers, and move to the next phase to be switched.
Upon switching the second phase, one of the sides had the wrong phase exposed. After line workers made the jumpering connection, phases were crossed. When the switched was closed it caused a phase-to-phase fault. This exposed both workers to a high-energy arc flash.
Figure 1:
E-box switch with the cover off
Figure 2:
E-box switch with connectivity shown
Figure 3:
E-box switch with connectivity shown from a view on the back
Figure 4:
Oil switch used outside the structure
Figure 5:
E-box phase jumpers in position with one blade being removed
There were several contributing factors to the event:
Normally, the line workers work in line, meaning the phase positions are on the same row. In this case, the E-box was mounted too high on the wall to do the work in a normal standing position. There wasn’t room to install two ladders, so the crew decided to have one person on the ladder to switch the top-right quadrant, and the other worker stood on the floor to switch the bottom-left quadrant (see Figure 6). Electrically, the switching operation works the same, but the phases are no longer in-line horizontally. The first phase was successfully removed (Figure 7). On opening the second phase, the position in the bottom left was not moved, so phases were crossed (Figure 8).
The feeder breaker at the substation failed to open. The bank breaker (the backup protection) operated, but the duration of the fault was about two seconds. The fault current was about 10 kA. LADWP estimated that it was a 60 - 80 cal/cm² exposure. With normal clearing speeds of the feeder breaker (6 to 9 cycles), it would have been roughly a 5 cal/cm² exposure. Fortunately, it was a cold day, and the worker with the most exposure was wearing three arc-rated layers: shirt (4 cal/cm²), a heavy sweatshirt (38 cal/cm²), and coveralls (8 cal/cm²). Normally, only the shirt and the coveralls were required. Both workers were also wearing 12-cal/cm² face shields. See Figure 9 for damage to PPE.
Workers removed the entry ladder because there were space constraints. The workers were not tethered.
There was some pressure to move through this quickly. The crew was on a 16-hour workday.
Figure 6:
Setup during this switching operation
Figure 7:
Application of the switch leads and successful removal of the blades on the first phase
Figure 8:
Jumper positioning that crossed phases
Figure 9:
PPE damage
LADWP made several changes based on this incident:
Stopped performing live open and close operations on these E-boxes. LADWP will still parallel and separate with another circuit.
Started an aggressive circuit-breaker maintenance program. In addition, circuit breakers must have cycled within the last year prior to live work in a structure. If not, they will cycle the breakers prior to work.
Introduced new training methods.
Required a balaclava in addition to the face shield (facial burns were the main injury in this event).
Developing a plan for E-box replacements.
Utility Self-Review Questions
These are review questions identified. Utilities can use these as
self-review questions to review internal procedures and equipment.
Do we have reasonably fast backup protection? Do we have breaker failure protection?
Are circuit breakers regularly maintained?
Do we employ fast relay settings when in a hot line tag?
Do we have this type of switch or other underground switches with unusual switching requirements?
Do we use any custom tools or switches that have nonstandard operations?
Do we monitor and/or limit extended work periods?
Do we require tethering in underground structures?
Ideas to Reduce Risks
These are ideas proposed during brainstorming. They include speculative ideas.
Color code phases. Every position could have a color / label.
Use tinted covers that are color coded.
Use three sets of color-coded leads, so workers have to grab a new set.
To ensure that the work can be done at the same level, use scaffolding or other step stool.
Apply limits on the work day.
If the entry ladder comes out, require tethering.
Stud or dimple the switch ends, so workers can attach the leads then exit the structure to switch from above.
Enable a fast hot line tag to reduce duration. One could also speed up backup protection.
Increase maintenance on circuit breakers.
Add fast breaker-failure protection. Normally, breaker-failure protection is slow, but a hot line tag setting could speed that up.
Add documents to training to require steps for communications (the top switch operator needs to hear, too).
Add capabilities to the homemade switch used for phasing. The switch could use a vacuum interrupter with a voltage sensor. The voltage sensor could see the cross phasing, and the switch could block closing.
Replace E-boxes with a safer design. Suggestions included:
For the tightest locations, use elbows on bus bars. Ideally, arrange these so they can be operated with hotsticks from the sidewalk. Even if they have to be operated within the structure, the hotsticks add distance to the worker.
If there is no space, go back one section on the circuit, and install solid di-electric switches.
If there is room, Trayer / Innovative Switch has a three-way switch. Gang two together if four-way operation is needed.
One event involved arcing caused by cable testing initiated elsewhere; a second event involved a switching error and applying a ground without checking for voltage
Event #1: Cable Testing caused Arcing in another Structure with Workers
Here are the steps involved in the incident.
Relay and cable crews were working a trouble call to locate a fault on circuit PK02.
After identifying the location of the fault, two relay crew members staged the testing trailer at manhole 8853 to test the remainder of the circuit away from the substation.
After staging the job, both members entered the vault where grounds were hung on the load side of switch MP0218.
The crew members removed the grounds to conduct testing, but left the switch closed.
After observing manhole 8853 was clear, the relay crew members began testing.
Three cable crew members were working in the manhole, when voltage from the test equipment back-fed on the circuit, causing the cables to arc. Fortunately, there were no injuries.
CenterPoint Energy identified several key factors involved in the event:
A tailboard did not occur with new cable crew members and relay crew members.
Crew members were using phones for communications (radios would have allowed better communication between the cable crew and the relay crew).
The head journey worker left the site to go get a drink.
The relay crew did not open the switch after removing grounds in the vault (grounded on the load side).
Relay crew members did not communicate they were testing on the circuit.
No employees should be in a vault while testing is being conducted.
Utility Self-Review Questions for Event #1
These are review questions identified. Utilities can use these as
self-review questions to review internal procedures and equipment.
Do we require a separate clearance to test a circuit?
Do we require a common job briefing for cable testers and crews on the circuit?
If the crew leader with the clearance leaves the scene, are there procedures on what’s allowed and what’s not?
Ideas to Reduce Risks for Event #1
These are ideas proposed during brainstorming. They include speculative ideas.
Require use of radios for communication when testing cable. That allows other workers in the vicinity to hear about work that might affect them.
Require a separate clearance to test a circuit.
Require the work clearance to be released prior to testing (high pot or pickup test at voltage). Require an okay from dispatch. Grounds are still installed.
Implement a system where the control center can see where workers are at on given circuits and structures.
Require a common job briefing for cable testers and crews on the circuit.
Event #2: Switching Error and Flash when applying a Ground
Here are the steps involved in the incident.
Major underground relay and cable splicer crews were tasked with switching, grounding, and replacing a switch and transformer.
Upon completion of switching by the relay crew, the cable splicer crew began applying protective grounds at three separate locations.
After applying grounds at one location, two cable splicers relocated to where the switch and transformer would be replaced to assist with other tasks.
One of the two cable splicers began to assist with grounding the switch to be replaced. He started by checking the load side of the switch with a hot line indicator, and it was verified de-energized.
He then proceeded to the line side of the switch where he picked up a hot stick with a ground attached and attempted to discharge capacitance on C phase.
As he touched the ground to the switch spade on C phase, the equipment flashed (see Figure 1). An onsite investigation revealed a switching error occurred which left A, B, and C phase hot on the switch. Fortunately, there were no injuries from the incident.
Figure 1:
Line side of the switch where the arc flash occurred.
CenterPoint Energy identified several reasons for the issue:
Absence of voltage was not verified prior to applying the ground.
Communication between crew members needed improvement. The cable splicer applying grounds did not communicate with the job lead.
A switching error occurred allowing the presence of energized equipment.
The switching error was at an upstream switch involving two circuits. The worker opened the normally closed switch and closed the normally open switch. The directed action was to open the normally closed switch and tag it. It also turns out that the switching operation at this switch was unneeded. Another switch upstream of this was also opened.
Utility Self-Review Questions for Event #2
These are review questions identified. Utilities can use these as
self-review questions to review internal procedures and equipment.
Do we require all switching actions to use three-part communications where each step is repeated back?
Do we require a face shield when applying grounds?
Is grounding a two-person action?
Ideas to Reduce Risks for Event #2
These are ideas proposed during brainstorming. They include speculative ideas.
Require a face shield when applying grounds.
Use voltage verification prior to grounding.
To avoid switching errors, require every switching step to be communicated back.
After switching actions to de-energize, include another verification step where voltage is checked downline of the open location.
Require grounding to be a two-person action. Both have to agree on steps (including voltage checks). That way, a single person cannot make a mistake.
Use a hot line tag that includes a fast trip.
1.3 - Contact and 120-V Electric Shock in a Structure
A worker contacted exposed 120-V leads due to insufficient isolation
Two workers were working in a structure cutting 120/208-V, 500-kcmil copper services to re-energize cables to the customer.
Cables were found to be in bad condition, so they replaced the cables to make the connections to the new customer. The work location was tight (Figure 1).
Distribution Mechanic “A” received an electrical shock while preparing to make a secondary connection. The conductor made contact at belly level when the backside of the worker was touching a grounded network protector.
The Distribution Splicer pulls Distribution Mechanic “A” away from the energized conductor.
Figure 2 notes several key locations involved in the event. Several metalic grounded objects were left exposed.
Figure 1:
Work location
Figure 2:
Work location with key locations noted, including exposed grounded parts
Con Edison determined the root cause as insufficient isolation from potential grounds within the work area.
Human performance issues included insufficient situational awareness, inattention to detail, and insufficient peer check.
Con Edison identified several precursors involved in this event:
Vulnerability to high energy: High energy hazard was not recognized or understood. Accessible high energy was not controlled.
Poor work planning: The job briefing was not performed or was of low quality.
Outside safety influences: The supervisor was not party to the safety briefing and did not visit the site.
Utility Self-Review Questions
These are review questions identified. Utilities can use these as
self-review questions to review internal procedures and equipment.
Do we have sufficient safety culture to prevent workers from getting lax around scenarios they think are “easy” or “safe”?
Do workers reliably use cover-up in 120/208-V scenarios? Do supervisors verify cover-up activities?
Ideas to Reduce Risks
These are ideas proposed during brainstorming. These include speculative ideas.
Use pre-job inspections to identify hazards to determine controls needed like cover-up.
Use Tenite boots to cover the connector end, so you could make the crimps prior to connecting to the energized part.
Educate workers around this type of incident. Have constant conversations of events like this. Remind workers that seemingly low-risk work like 120-V cables can have high energy.
Have the supervisor verify rubber-up (in person or by video review).
Require photo documentation of cover-up.
Use rubber caps on the ends of cables. In this case, the shock happened during the final stage after the cap would have been removed.
Use a smaller network protector, so there is more room in the structure.
Use an insulating rubber apron to protect the worker (this also has ramifications as it would likely be cumbersome and hot).
Provide easier options for applying rubber blankets. Provide magnets for attachments to cabinets or other objects that are difficult to clip to.
1.4 - Contact Incident in a Padmounted Switch
A cable splicer was shocked when another splicer inadvertently connected the other end of the cable to an energized, uncapped bushing
A section of cable between a padmounted PME-9 switch and a padmounted cable faulted (Figure 1).
Fault locating determined the section of cable to be faulted (the section was approximately 20 ft in length), and a generator was installed at the transformer to pick up the load.
A composite crew was assigned the task of replacing the faulted section, making 200-A elbows at both the switch and transformer, switch the section back, and remove the generator.
When the construction inspector and composite crew arrived on the job, they reviewed the situation and conducted a job brief.
The construction inspector observed the faulted section open with both sets of elbows (in the switch and transformer) in the open position and placed in a feed-thru stand-off bushing.
The construction inspector requested clearance from Dispatch to ground the faulted cables and cut them, so the section of cable could be removed.
The cable was cut, the section of cable was removed, and a new section was installed.
Two underground line workers were assigned the task to make three elbow terminations in both the switch and the transformer.
The bushings at the switch were uncapped and open as an insulated cap had not been installed.
At the switch location, the underground worker completed two of the elbows and then installed them onto the open bushings of the switch (Figure 2 and Figure 3). He did not realize that this energized the cables into the transformer. The exposed bushings were right next to the parking-stand bushings.
The underground worker working in the transformer (Figure 4) was prepping the cable ends to install the last elbow when the cable became energized at 8 kV.
The underground worker who was working bare handed suffered electrical contact to his left thumb and middle finger.
The fuse in the PME switch tripped to limit the duration.
The tags were also applied incorrectly to the elbows of the disconnected cables. Tags should mark the limit of the work zone, so in this case, they should be applied on the capped bushings.
Figure 1:
Work area with the transformer in the foreground, the switch in the background, and the generator on the left
Figure 2:
Switch location with two elbows made and locations where bushings were exposed (the yellow grounding elbows were still installed)
Figure 3:
Switch location as it should have been made with bushing caps installed and cables parked on the grounded parking stand
Figure 4:
Transformer work location
Eversource Energy identified several takeaways for discussion:
Communication needs to be thorough with all crew members especially during critical stages such as connecting equipment back on the system.
Control of Energy Source and the boundaries must be identified, fully understood by the entire crew and documented as part of the Job Brief.
The supervision of the job; be it a line supervisor, crew lead, construction inspector, or other crew members is critical to identify any potential hazards at the job brief and as the work progresses so all understand the status and hazard controls needed to keep people safe.
Eversource Energy determined that the root cause was that all field personnel did not identify an exposed energized part in the immediate work zone (un-capped bushing) which was outside of the Master Work Tag (MWT) zone.
Several contributing factors were identified:
Failure to follow work procedures:
Not capping the energized bushings
Not using 200-A stand-off/parking bushings to park newly made elbows
Poor communication: Employees working within proximity to one another did not communicate with each other regarding steps each was
taking. The Job Brief was unsatisfactory: they failed to utilize the job brief to facilitate discussion around what is energized and what is de-energized.
The crew did not understand their clearance boundaries defining the zone of protection.
Eversource Energy took several immediate actions based on this incident:
Established a significant-incident conference call for the leadership team.
Implemented a company-wide stand down to review the event and immediate lessons learned.
Assembled an IA team to review events and establish corrective actions to prevent reoccurrence.
Several corrective actions were implemented:
Review Switching and Tagging procedures with Management.
Additionally, require field supervisors to carry a copy of MWT/switching instructions/Clearance boundaries.
Set expectations for supervisors that it is mandatory to review MWT/Clearance boundaries with the clearance holder when arriving on the job site.
Review and reset expectation on landing elbows for Supervisors, CI/TS and underground lineworkers.
Reinforce that the Construction Inspector or Troubleshooter are the only Job classification qualified to land Elbows on bushings.
Attendance mandatory for all affected personnel.
Issue Written Guidance and set expectations for Supervisors on Job assignment work Packages.
Develop team of represented and management to collaboratively work on expectations for work packages.
100% Supervisory attendance Mandatory for review of developed expectations.
Job Briefs Improvement Process.
Director (Ops) daily review of Job Briefs.
Independent review (Safety) of Job Briefings.
Report out by Manager and Supervisors.
Utility Self-Review Questions
These are review questions identified. Utilities can use these as
self-review questions to review internal procedures and equipment.
In dead-front equipment, do crews ever leave bushings uncapped? Are supervisors required to check for this?
Are crews allowed to work both ends of a cable at the same time? Are there any limits?
Do workers get complacent when doing relatively easy jobs?
Do we require that workers check for voltage prior to parking elbows?
Is this type of tagging error common for us (tagging the elbows rather than the bushings)?
Ideas to Reduce Risks
These are ideas proposed during brainstorming. They include speculative ideas.
Work one end at a time. Ground the remote end.
Only allow simultaneous work at both ends if the work locations are visible, and each end can communicate easily.
Require a voltage check prior to parking an elbow.
Require that a supervisor check that bushings are properly capped and tagged.
Instead of a cap that must be grounded, consider a fully insulated cap to simplify capping the bushings. A meeting participant noted that these aren’t submersible and didn’t think they stayed on the bushing as well.
Take photographs of bushings that are properly capped and tagged for verification.
Require separate documented moves for key actions. Capping and tagging could be separate steps. Checking for dead and parking an elbow could be separate steps.
Open and tag out the PME switch to de-energize the fuse side and provide a visual open.
Find better places for feed-thru parking stands, so it is more obvious where cables should be parked, and they don’t get confused with the (possibly live) equipment bushings. In this case, on the right side of the compartment in Figure 2, there is room for multiple parking stands. A level below the existing bushings is another option. With an adjustable-bracket, four-point feed-thru (example), the three cables could be parked along with the grounding cable. The length and stiffness of the cables may restrict the placement of parking stands.
Color code parking stands differently, or add special markings.
Leave the fuse out to keep the cable de-energized and provide a visual open. Troubleshooters would have to re-visit the site to install the fuse, or provide the splicing crew with training and authorization to install fuses.
Have a single crew that can do everything, including the switching and tagging and the repair work. This would reduce miscommunication issues and force crews to understand the layout better. It would also make it more natural to leave the fuses out until the end.
1.5 - Contact and Arc Flash due to Cutting into an Energized Cable
A line worker was electrocuted and another had an arc flash when a worker cut into an energized cable
Two journeymen line workers were working in a vault with multiple cables. This project was part of a large downtown conversion and upgrade that they had been working for several weeks. Both had more than 15 years of experience.
A journeymen line worker began preforming a splice removal on the wrong cable.
The worker did not test for voltage prior to starting to remove the Y splice.
Journeyman 1 made phase-to-ground contact and was electrocuted. Journeyman 2 had an arc flash but was able to exit the structure.
The control center reclosed on the circuit, and additional circuits became faulted.
This event happened on the night shift on a Monday after 10 PM. Earlier in the day, the workers reported for work in the morning as part of a four-hour swing shift. The normal schedule for them was to report Monday morning then work night shifts the rest of the week.
APS identified several causes for the event:
Lack of mutual understanding of the scope of work.
Failure to perform voltage testing prior to Y-splice removal.
Crew dynamics and communication.
APS’s main lessons learned were:
The de-energization process needs review.
Safety retrieval system needs review.
Corporate emergency response needs review.
Utility Self-Review Questions
These are review questions identified. Utilities can use these as
self-review questions to review internal procedures and equipment.
Do we require cutting of medium-voltage cables to be done remotely? Is this followed in the field?
Do crews always test for voltage prior to cutting cables?
Does the control center know which structures and which circuits may have active work? Do operators ever reclose without a circuit patrol?
For night work, do we have the short swing shift at the start of the week? Do we monitor the work schedules and the mental state of our workers? Do we give breaks or otherwise limit night-shift work?
Ideas to Reduce Risks
These are ideas proposed during brainstorming. They include speculative ideas.
Always require remote cable cutting unless the cable is grounded within visual range, and the crew can physically touch the cable to the point of the cut. Require all personnel to be out of the structure during the cutting operation.
Require heavier arc-rated clothing (cals) for in-structure cutting.
Require rated rubber gloves during local cable cutting.
Require and use a safety retrieval system.
Implement electronic testing and identification of cables. This system applies pulses or other signals after a circuit has been grounded. This allows precise location and tagging of cables in the structure.
Require physical tagging to be done before workers arrive at the location.
Require control-center control of testing and cutting steps.
Require the person testing dead to be the person calling the control center for clearance.
Require voltage testing and cutting operations to be a two-person communication and authority.
Require two access points into structures to ease getaway.
Don’t allow the “short swing” where night-shift workers come in during the morning shift at the beginning of the week.
On Mondays with the short swing shift, assign easier work or less work.
Use a portable video camera in the structure to allow a supervisor to monitor work and to use after the fact for evidence gathering.
Implement a system between the control center and field personnel to identify every structure where personnel may be working. Tie these locations to feeders. Tag these feeders so operators do not reclose on circuits with active work.
Train operators to limit reclosing, particularly when work may be present on that feeder.
Apply the hot line tag to every feeder in the structure where work is being performed. Implement instantaneous protection as part of this hot line tag.
Use CLIP fuses which are triggered current-limiting fuses for underground feeders. These can reduce fault currents and operate very quickly.
A crew was dispatched to replace a pole from recent storm activity.
The crew include the line worker in charge and a journeyman line
worker.
The crew set up their digger derrick to replace the pole in the right
of way (Figure 1).
The journeyman line worker was reaching to grab chains near the back
of the truck (Figure 2) when the boom of the truck contacted the
7200-V primary (Figure 3).
The line worker became the ground path and was electrocuted.
This incident happened right at the beginning of the work as the crew
was preparing to lift the pole off of the truck.
Figure 1:
Digger derrick position at the accident scene
Figure 2:
Back of the digger derrick
Figure 3:
Location of the primary contact
The main contributing factors to the incident were:
Insufficient tailboard
Failure to follow Minimum Approach Distance (MAD) standards
No designated spotter for derrick boom operations
No vehicle grounding or barricades
The truck was positioned well off to the side of the road. This was
likely done to leave the road open to traffic. This road had high
traffic. If the lane was blocked, it would have required traffic
control. The truck positioning had an impact because (1) the truck was
closer the the vertical plane of the conductors, and (2) the truck was
leaning, and that tilt put the boom in line with the phase conductor.
With the location of the boom controls, the operator had poor line of
sight to the position of the boom and to the location of journeyman line
worker at the back of the truck.
The line worker on the ground was not wearing rated rubber gloves or
other insulating PPE.
Consumers Energy took several immediate actions based on this incident:
An Incident Command System (ICS) was stood up to coordinate response
and to provide support for affected headquarters.
A Root-Cause Analysis (RCA) Team was convened and started investigation
immediately with team made up of both union and management.
Safety Interventions were conducted across all Operations, focusing on
improving the quality of tailboards, traffic control plans, stop the
job, and following procedures.
A Leadership Safety Intervention webinar was presented that resulted
in:
All tailboards are to be reviewed by Field Leaders daily.
Field Leaders will Stop the Job where tailboards are not completed
on job sites and return crews to the headquarters to perform the
tailboard with the Field Leader and Union Leadership and begin
Safety Positive Discipline for repeat findings.
Every Employee will be observed once every two weeks.
The union began owning the Wednesday Safety Stand-up Meetings across
all Operations with a focus on review of Safety Standards and Work
Methods.
Three-person crews are required for all work requiring digger derrick
boom operations, and a designated safety watcher is required.
Consumers Energy partnered with EPRI to review grounding practices for
distribution work.
Experienced and respected team of management and union went to every
headquarters and presented root-cause analysis findings.
Other longer term actions included:
Reviewed coverup requirements and provided training based on best
practices.
Evaluated both proximity probes as well as personal devices to provide
warning of “Live Line”. Partnered with EPRI and other vendors.
Changed the cultural practice of why should it be acceptable to work
it “Live” versus “Dead”.
Utility Self-Review Questions
These are review questions identified by participants during
brainstorming. Utilities can use these as self-review questions to
review internal procedures and equipment.
Do we staff for and apply a spotter?
Do we have proper coverup procedures?
What PPE do we require that could have protected in this scenario?
Do we do risk analysis around peripheral tasks related to the main task?
Do field workers use any inappropriate grounding methods? Local,
temporary grounds are ineffective and increase hazards.
Do existing job briefings cover hazards sufficiently? Is the positioning and the tilt of the vehicle considered?
Do employees understand bonding for their protection? (and the whole concept of EPZ)
Do we need to consider any of the improvement options listed below?
Ideas to Reduce Risks
These are ideas proposed during brainstorming. They include speculative ideas.
Rubber everything up on the pole top.
Require dielectric-insulated footwear.
Require insulated gloves when touching a vehicle or other object that
could make contact. Note that this will not protect against step
potentials if the truck becomes energized.
Require digger derricks to be grounded. Use approved grounding points,
particularly a connection to the system neutral.
Use suitable barricades, and limit access to the truck unless using
appropriate PPE.
Require a designated spotter.
Use and test insulated digger derricks.
Use proximity sensors on the boom.
Use remote boom controls for better visibility of the work in the air
and to coworkers on the ground.
Develop and implement LIDAR-based proximity mapping and avoidance of
contacts.
The workers were reconductoring a circuit. Layout arms were used to spread out existing conductors to make room to install new conductors.
Figure 1 shows an example of layout arms applied. In this event, one layout arm broke free, and the conductors swung upward due to uplift forces.
Figure 1:
Example of layout arms used to separate conductors
Here are the steps involved in the incident.
A layout arm was installed on a new fiberglass tangent crossarm arm to temporarily hold conductors. Automatic reclosing was disabled prior to work.
Two phases of 1/0 Al were transferred to the layout arm (255 ft and 186 ft spans). There was a 4° angle. Adjacent poles were taller causing uplift on conductors.
The line worker had tightened down on the eye screws to secure the rubber stoppers to each side of the new fiberglass arm.
The line worker repositioned the aerial lift to the opposite side of the pole and noticed the layout arm was moving upward.
The phases contacted the crossarm and a flash occurred resulting in a circuit outage.
Figure 2:
Position of the layout arm after it it lifted off the crossarm
The main contributing factors to the incident were:
Crews were unfamiliar with layout-arm application on fiberglass arms.
The layout arm has a hanger which goes over the top of the arm and a saddle on the end closest to the pole which goes under the arm. Both are designed to support downward loading.
Under uplift, only the rubber stoppers prevent movement from the upward force on the conductors.
This is not an issue on wood arms because the the layout arms for wood arms have a spike that penetrates the wood to secure the temporary support (Figure 3).
Figure 3:
Layout arm with spikes that secure it to a wooden crossarm
Using equipment from two different manufacturers, the utility tested the ability of the rubber stopper to support during a pull test. They found that manufacturer 1 began to slip at 250 lbs. Manufacturer 2 began to slip at 800 lbs. Manufacturer 2 used a rubber stopper with a larger diameter. The utility found that a 250-lb limit of slip at the rubber stopper corresponds to a 55.6-lb uplift on two conductors.
There is no guidance from vendors on torqueing the rubber stopper and no guidance on use when there is uplift.
Dominion Energy made several changes based on this incident:
Wrote a guide on working with these layout arms on fiberglass crossarms. This is available to field workers on their internal information-sharing platform.
Provided guidance on uplift: if uplift is more than 60 lbs, these layout arms are not to be used.
Included guidance on this scenario in training.
Developed a clevis-pin design to hold the layout arm in place. See page 12 in the presentation.
Dominion Energy also presented on other learnings on use of fiberglass crossarms. They had issues with over-torqueing, so they forbid use of impact drivers. They found that washers should be at least 3 in to limit cracks in crossarms. They also switched from a wall thickness of 0.20 in to 0.3125 in to limit cracking.
Utility Self-Review Questions
These are review questions identified by participants during brainstorming. Utilities can use these as self-review questions to review internal procedures and equipment.
Do our field crews use this tool?
Are field crews aware of hazards when there is uplift on conductors?
Do my written practices cover this scenario?
Is this scenario addressed in training?
Are there materials or practices we need to change (like moving to a heavier wall crossarm)?
Can field crews identify alternative approaches when there is uplift?
Should we identify alternative options like those discussed below?
Do we have internal procedures in place to evaluate safety issues when new tools or equipment are introduced? Do we involve workers to try to identify issues with changes or introduction of new equipment?
After introduction of new tools or equipment, do we have a process to circle back and engage the end users of the equipment?
When an issue is found, do we have procedures in place to share knowledge within the company?
Ideas to Reduce Risks
These are ideas proposed during brainstorming. They include speculative ideas.
Do not use these layout arms when there is any uplift on conductors. Use an alternative approach, like bolting another crossarm to the existing crossarm.
Leverage existing holes in the crossarm to use a penetrating pin. This avoids the pressure connection with the rubber stopper. On wood crossarms, the layout arms have a spike (penetrating pin) which penetrates the wood and holds for both upward and downward pressure. With holes, the same tool can be used for wood and fiberglass crossarms. If no holes are available, drill holes as needed to use the spike.
Specify a cross arm with a predrilled hole in it to allow use of the layout arm with the penetrating pin (such as used on wood crossarms).
To prevent the uplift, apply a strap or tether around the layout arm and crossarm near the rubber stopper.
Work with vendors to design a tool with a C-clamp instead of a rubber stopper. Another option is to use a clevis-style attachment to anchor the inside part of the layout arm to the crossarm.
Use a textured arm to enhance friction for the rubber stopper.
As part of training, show workers that this tool may fail to hold if there is uplift. Provide alternatives.
Put a sticker on the arm that describes how it should be used.
Put a QR code on the layout arm that brings up directions, hazards (like uplift) and alternative options.
1.8 - Shock after a Transformer was Test Energized Before being Properly Grounded
A ground worker was shocked when connecting a down-ground lead to a ground rod while a transformer was “test energized” above
A four-person line crew was replacing a pole with a single-phase
transformer.
The system voltage was 13,200 GrdY/7620 V with a 120/240-V single-phase
secondary.
A line worker working aloft in bucket truck test-energized newly
installed transformer to check for proper voltage.
When the fuse was installed, energizing the transformer, a ground
worker was in the process of connecting the grounding conductor to the
driven ground rod at the base of the newly set pole.
The ground worker was wearing dielectric overshoes and wearing leather
work gloves.
While the ground worker was connecting the grounding conductor and the
ground rod, the worker felt a shock. See Figure 1.
At this point the grounding conductor and the new transformer were not
connected to the system neutral.
The transformer neutral bushing was connected to the transformer tank
ground and connected to the grounding conductor when energized. The
grounding conductor was also stapled to the pole.
The affected worker was not aware the line worker in the bucket had
energized the transformer, and line worker aloft was not aware that
the ground was not fully connected.
Figure 1:
Picture of completed ground installation
The main contributing factors to the incident were:
Engineering Controls / Isolation: The crew failed to properly
connect the transformer to the system neutral and connect the down
ground prior to energizing the transformer.
Administrative Controls: Work practices, policies, and field guides
were not followed.
Administrative Controls: Exposure (voltage/amperage) not recognized,
eliminated, reduced, or controlled.
Administrative Controls: Exposure to the hazard occurred due to
ineffective communication among crew members throughout the completion
of work. Communication was unclear between working aloft and
groundman.
Personal Protective Equipment: PPE is the last line of defense when
other safeguards break down. Class 2 (20 kV) rubber gloves are
required in this task of connecting a ground rod and grounding
conductor where the grounding conductor is already run up the pole.
The company’s Accident Prevention Handbook (APH) related to working on
distribution transformers includes the following requirements:
APH 407.2 When connecting equipment to an energized circuit, the
connection to the energized circuit must be made last, and when
removing, must be disconnected first. The equipment neutrals (where
required) and grounds must be connected first when installing and
disconnected last when removing.
APH 407.3 Unless properly grounded, transformer cases must be
considered as energized while the transformer is connected to the
circuit.
If a transformer is energized without a connection to the system neutral
or a pole ground, the transformer and pole down lead will float to
primary potential (7620 V in this case). That is a hazard for the
workers in the air and for workers on the ground near the down lead.
When the ground worker was making a series connection to the ground rod,
the electrical path from the transformer to ground could have been
through the person from hand to hand. With that path, the exciting
current from the transformer will flow through the person (see Figure
2). For a 25-kVA transformer at 7620 V, this is about 33 mA if the
exciting current is 1%. Larger transformers would have more exciting
current. A current of 33 mA is above the median let-go current for men
(16 A) and above the median for breathing difficulty (23 A) using
thresholds from an IEEE working group 1. When the transformer
is first energized, the current can be 25 times larger. With the pole
ground stapled to the pole, the pole also provides a path to ground.
That may have conducted the inrush prior to the ground worker making
contact.
Figure 2:
Worker in the series path when making a ground connection
The incident also highlights another safety issue. The ground worker is
right under the work being performed in the air and is at risk from
falling tools and equipment.
FirstEnergy identified several lessons learned and key takeaways:
Constant communication between crew members is vital to ensure work is not
inadvertently exposing someone to hazards. Pause work when unsure of
a task. Utilize three-part communication, especially at critical steps of
the job, such as when energizing equipment.
Avoid handling two different electrical potentials, exposing oneself to shock.
Don PPE as a last line of defense when other safeguards break down.
Utilize Human Performance tools such as the two-minute drill when job
scope changes or there is an adjustment to crewing compliment.
Even when testing equipment for proper voltage, perform necessary
connections relative to the system voltage. In this case (13200 GrdY/7620 V),
attach the transformer neutral to the system neutral prior to energizing.
Complete all grounding and neutral connections, including: the ground
rod, grounding conductor, system neutral, and equipment grounding prior
to energizing equipment.
On a transformer with a single-bushing design, one end of the primary
winding is internally connected to the tank and can potentially energize
the tank at 7620 V.
During energization, even unloaded transformers can exhibit
magnetizing inrush currents. These currents can be up to 25 times the
normal full load current of the transformer, but this only lasts for a
few cycles. Thisi s enough to cause a shock but too fast to measure
without specialized metering equipment.
The primary coils to the transformer structure also create a capacitive
circuit that can exhibit a capacitive inrush or charging current when
the transformer is energized.
As a response to this event, the company performed an incident review
including a reenactment. they published a Safety Snapshot that is shared
with employees. As needed, they verify that employees are aware of the
potential hazards present with grounded equipment and are aware of
potential exposure.
Utility Self-Review Questions
These are review questions identified by participants during
brainstorming. Utilities can use these as self-review questions to
review internal procedures and equipment.
Do my employees identify this as a hazard? (energizing a transformer
without a proper ground connection)
Do we have a requirement for rated gloves when connecting grounds?
Would we identify energizing a transformer as a critical step? (to
force everyone to stand back)
Do we have a defined sequence of work for this operation?
Do we have periodic training over time to cover this type of risk?
Should we do a “safety alert” for this?
Do I give my employees time to avoid pushing human factors (like
rushing)?
Does the job briefing flag factors involved, including human factors?
Ideas to Reduce Risks
These are ideas proposed during brainstorming. They include speculative
ideas.
Improve distribution transformer training for line and engineering to
include this risk.
Stand down across the region to discuss issues.
Require that crews confirm that everyone is in the clear prior to
energizing.
The ground worker should communicate up to the crew above, too.
As a possible check on next steps, the ground crew would not send up
the hotstick until everyone agrees.
For replacements for grounding conductors when stolen, use quick-bond
cables like jumper cables to bypass to prep for full replacement.
Require two tank grounds.
Hype up the importance of the neutral and associated hazards. Without
the neutral connection, the transformer floats to primary voltage.
Use a hotline tool for bonds / grounds.
Find a ground wire connection you can make without getting in series.
There is existing tech with a hammer-type mechanism to make a
connection.
IEEE Working Group on Electrostatic and Electromagnetic
Effects, Delaplace, L. R., and Reilly, J. P., “Electric and Magnetic
Field Coupling From High Voltage AC Power Transmission Lines —
Classification of Short Term Effects on People,” IEEE Transactions
on Power Apparatus and Systems, vol. PAS-97, no. 6, pp. 2243–52,
November/December 1978. ↩︎
2 - 2023 Overhead Distribution Serious Injury and Fatality (SIF) Workshop
Participants identified the following hazardous scenarios:
Failing to identify an induction hazard.
Pulling wire above energized wire.
600-A solid blade disconnects in a porcelain housing. Operated with a hotstick.
Downed conductors over a highway. In an incident, a 23-kV conductor went across a big highway. How do we deal with equipotential and cutting it clear?
Old assets. At what point is something like a pole too old?
Capacitor banks putting current on system nuetrals.
Steel poles: they bring a ground into the work space, and they impactg other utilities (comms messengers have burned apart from fault current).
Manufacturer issues with new equipment. (grounding a cap bank for example).
Installing and removing overhead arresters?
Arc flash hazards and arc flash protection for workers in the overhead work space.
Old two-bushing transformers: case becomes energized at primary potential. Internal failure of transformer.
Transferring conductors with automatic splices (especially older copper wire) (loses tension when it relaxes).
Pole-top fires (transformers for example).
Misidentifying conductors. Mixing up secondary and primary.
Trees on conductors.
Stored energy during ice storms.
Automatic splices for guy wires had manufacturing issues (jaw problems; too much grease).
Failure to identify backfeed (from our own circuits or DER or other).
Wire watchers and damage assessors: downed wires and storm damage.
Hot-Line tag mode (one-shot to lock-out) and over-reaching down-stream fuses.
Working de-energized with “live” overbuild.
Brainstorming Technology Options
Participants identified the following technologies to consider:
Boom load indicator on a material handler.
Vehicle stabilization warning system: is the vehicle level, tip sensing, load limit sensing, 3D awareness of the boom, and equipment in the space around the vehicle including MAD clearances.
App for arc flash calculations; at this work location, this is the expected energy. Put this in the job briefing (by feeder).
Augmented reality to prep for work on a pole. Use a drone ahead of time to inspect and fill in hazard warnings on a job brief.
Robots to do the work.
Insulate the wire. Deenergize. Dielectric suit.
Proximity detector for hotsticking.
Job briefing app that can set up a virtual ‘remote observer’.
3 - 2023 Underground Distribution Serious Injury and Fatality (SIF) Workshop
Workshop to discuss ways to reduce SIFs
November 9, 2023, San Antonio, TX, hosted by CPS Energy
Held in conjuction with the North American Dense Urban Utility Working Group (NADUUWG). See the NADUUWG site for information and past presentations.
