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QUOTE
What are the Risks When Setting a Pole?
The workers at risk, while setting a pole in a live circuit, are the workers on the ground, operating the boom, controlling the pole butt and anyone standing near or touching the truck, trailer, grounding cables and/or ground rod. The workers most at risk are the people controlling the pole butt because that is where the greatest variables are. Depending on the voltage, the conductivity of the pole and the type of earth, the ground gradients around the pole can spread out at some unknown distance from the pole.
A safe procedure for setting a pole in a live circuit needs to focus on two main risks.
1. Reduce the risk of an accidental electrical contact with the boom or pole.
2. Reduce the risk of touch and step potentials for workers on the ground if the pole, truck, trailer, grounding cables and/or ground rod becomes energized.
Reduce the Probability of Accidental Contact
A standard work procedure to set a pole in a live-line requires the installation of insulated cover-up on the conductors and/or insulated cover-up on the pole. With the use of cover-up and an observer, a modern vehicle can set poles in a live-line without making contact with a bare live circuit. The measures taken to reduce the risk of an accidental contact would probably be the same for all types of poles. These measures can include:
Check for the viability of taking an outage.
Cover and/or spread-out the conductors.
Put covers or guards on the pole.
Use a dedicated observer/signal person.
Protect Workers Near or on the Truck
Protecting workers from touch and step potentials around a truck with a boom in the vicinity of a live circuit is another topic. Most utilities have procedures that include measures such as, a minimum approach distance, truck grounding, truck barricading, the wearing of electrical resistant footwear, staying on the operating platform and/or dedicated observers.
Reduce the Exposure Time to a Contact
The circuit breaker or recloser should be put in a non-reclose position and tagged to ensure that the circuit will remain isolated after it trips-out. When a circuit is kept from being reenergized, there will be a reduced exposure time to the hazard and if needed, it will be safer to carry out a rescue.
A pole setting procedure should take steps to promote a quick trip-out of the circuit and, therefore, exposure time to a ground fault, in the case of an accidental contact. Ground the truck to the best ground electrode available, which is the neutral on most distribution circuits. Grounding a steel pole to the same truck ground electrode will promote a quick trip-out after an accidental pole contact.
Protect Workers from Touch Potentials
A touch potential is the voltage difference between a worker’s feet on the ground and hands or another part of the body such as a shoulder touching the pole. If a pole (wood, concrete or steel) makes contact with a live circuit there will be touch potentials between the pole and earth. However, the more conductive the pole, the lesser the potential difference or touch potential between the pole and where the pole is touching the ground.
If no one is touching the pole, there cannot be any exposure to touch potentials. At transmission voltages, guide ropes are often tied to the butt to control the pole to provide protection from touch potentials. At distribution voltages, rubber gloves rated for the circuit voltage will protect a worker from touch potentials.
There is a perception that using pole tongs (pole handler) along with rubber gloves is meant to provide additional insulation for higher distribution or subtransmission voltage. The original purpose of pole tongs is for protection from step potentials. Pole tongs keep the worker away from the pole where the highest step potentials are. It is true that epoxy tongs provide additional insulation from touch potentials, but officially they cannot be considered insulation unless they are stored, maintained and retested like a live-line tool.
Protect Workers from Step Potentials
The weakest part of most pole setting procedures has been the measures prescribed for protection from step potentials.
Electrical current flows into the earth (ground fault) when an object such as a pole accidentally makes contact with an exposed live conductor. Where the pole touches the earth, there would be a rise in voltage relative to any earth farther away from the base of the pole. A step potential is defined as the voltage difference between two points on the ground separated by the distance of one pace or 1 meter.
The current will take many paths as it flows through the earth away from the pole. The voltage at the base of the pole will be higher than the voltage farther away. The earth acts as a network of resistors and the voltage will drop as the current flows through these resistors. The voltage or potential gradient around the base of the pole is often described as being like the ripples in a puddle after dropping a stone in the middle. There is a voltage difference between each ring of ripples and the voltage decreases with the rings farther from the center. A step potential refers to getting one foot on a high voltage ring near the base of the pole and the other foot on a lower voltage ring farther away from the pole. Voltage gradients are also known as ground gradients, potential gradients and step potentials.
When a fault-to-ground occurs, the current will flow through the earth back toward the source through the easiest paths available. In other words, during a ground fault there is not any way to know where and how far the ground gradients will travel. The return flow can be into the earth, back up any ground wires to the neutral, along fences, creek beds and so on. If the derrick truck is grounded to the neutral then the return path for much of the current could be back to the truck and up to the neutral.
The workers at risk, while setting a pole in a live circuit, are the workers on the ground, operating the boom, controlling the pole butt and anyone standing near or touching the truck, trailer, grounding cables and/or ground rod. The workers most at risk are the people controlling the pole butt because that is where the greatest variables are. Depending on the voltage, the conductivity of the pole and the type of earth, the ground gradients around the pole can spread out at some unknown distance from the pole.
A safe procedure for setting a pole in a live circuit needs to focus on two main risks.
1. Reduce the risk of an accidental electrical contact with the boom or pole.
2. Reduce the risk of touch and step potentials for workers on the ground if the pole, truck, trailer, grounding cables and/or ground rod becomes energized.
Reduce the Probability of Accidental Contact
A standard work procedure to set a pole in a live-line requires the installation of insulated cover-up on the conductors and/or insulated cover-up on the pole. With the use of cover-up and an observer, a modern vehicle can set poles in a live-line without making contact with a bare live circuit. The measures taken to reduce the risk of an accidental contact would probably be the same for all types of poles. These measures can include:
Check for the viability of taking an outage.
Cover and/or spread-out the conductors.
Put covers or guards on the pole.
Use a dedicated observer/signal person.
Protect Workers Near or on the Truck
Protecting workers from touch and step potentials around a truck with a boom in the vicinity of a live circuit is another topic. Most utilities have procedures that include measures such as, a minimum approach distance, truck grounding, truck barricading, the wearing of electrical resistant footwear, staying on the operating platform and/or dedicated observers.
Reduce the Exposure Time to a Contact
The circuit breaker or recloser should be put in a non-reclose position and tagged to ensure that the circuit will remain isolated after it trips-out. When a circuit is kept from being reenergized, there will be a reduced exposure time to the hazard and if needed, it will be safer to carry out a rescue.
A pole setting procedure should take steps to promote a quick trip-out of the circuit and, therefore, exposure time to a ground fault, in the case of an accidental contact. Ground the truck to the best ground electrode available, which is the neutral on most distribution circuits. Grounding a steel pole to the same truck ground electrode will promote a quick trip-out after an accidental pole contact.
Protect Workers from Touch Potentials
A touch potential is the voltage difference between a worker’s feet on the ground and hands or another part of the body such as a shoulder touching the pole. If a pole (wood, concrete or steel) makes contact with a live circuit there will be touch potentials between the pole and earth. However, the more conductive the pole, the lesser the potential difference or touch potential between the pole and where the pole is touching the ground.
If no one is touching the pole, there cannot be any exposure to touch potentials. At transmission voltages, guide ropes are often tied to the butt to control the pole to provide protection from touch potentials. At distribution voltages, rubber gloves rated for the circuit voltage will protect a worker from touch potentials.
There is a perception that using pole tongs (pole handler) along with rubber gloves is meant to provide additional insulation for higher distribution or subtransmission voltage. The original purpose of pole tongs is for protection from step potentials. Pole tongs keep the worker away from the pole where the highest step potentials are. It is true that epoxy tongs provide additional insulation from touch potentials, but officially they cannot be considered insulation unless they are stored, maintained and retested like a live-line tool.
Protect Workers from Step Potentials
The weakest part of most pole setting procedures has been the measures prescribed for protection from step potentials.
Electrical current flows into the earth (ground fault) when an object such as a pole accidentally makes contact with an exposed live conductor. Where the pole touches the earth, there would be a rise in voltage relative to any earth farther away from the base of the pole. A step potential is defined as the voltage difference between two points on the ground separated by the distance of one pace or 1 meter.
The current will take many paths as it flows through the earth away from the pole. The voltage at the base of the pole will be higher than the voltage farther away. The earth acts as a network of resistors and the voltage will drop as the current flows through these resistors. The voltage or potential gradient around the base of the pole is often described as being like the ripples in a puddle after dropping a stone in the middle. There is a voltage difference between each ring of ripples and the voltage decreases with the rings farther from the center. A step potential refers to getting one foot on a high voltage ring near the base of the pole and the other foot on a lower voltage ring farther away from the pole. Voltage gradients are also known as ground gradients, potential gradients and step potentials.
When a fault-to-ground occurs, the current will flow through the earth back toward the source through the easiest paths available. In other words, during a ground fault there is not any way to know where and how far the ground gradients will travel. The return flow can be into the earth, back up any ground wires to the neutral, along fences, creek beds and so on. If the derrick truck is grounded to the neutral then the return path for much of the current could be back to the truck and up to the neutral.
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