Insulating link
Encyclopedia
An insulating link is a device used on the hook of a crane
to electrically isolate the load or the crane wire line and superstructure in order to avoid potential undesirable effects of stray electrical energy. Uses include protection of crane operatives from the danger of electrocution
should the crane come into contact with a power line
, the control of currents generated by electromagnetic induction heating in processes such as metal smelting, and isolation of personnel or ordnance from currents generated by radio frequency energy as might be emitted by radio transmission towers. Insulating links are essentially robust insulators which prevent the flow of electricity through cranes or crane loads and into personnel working near the crane, or into other objects or systems which might suffer damage as a result.
of Western countries in the first half of the twentieth century. As early as 1931 there was a patent for an insulator that could be affixed to a crane’s wire rope or chain in order to prevent electrocution. Such early designs, however, proved unreliable because of their inability to operate safely in all construction crane environments.
By 1965 Federal law
mandated the use of insulating links on cranes in the United States. However, this requirement was lifted in the 1980s after an investigation found that lethal levels of electrical current could pass through the insulating links in use if they were wet and heavily contaminated at the same time. This investigation was sponsered by the crane industry as a defense for lawsuits involving power line contact. It was later proven that the tests were done using a kaolin mixture that is unlikely to be found at any construction site. However, the probability of simultaneous pollution, wetting and contact with the transmission line is rare. The occurance of these three events is less than 10%, in most of the USA. ( Performance Evaluation of insulating links used for worker protection in cranes, Dr. George G. Karady) This meant that insulating links were not widely used because of the crane industries legal liability.
The US Government introduced a new law in 2010 that mandates the use of approved insulating links in certain situations. The new law requires that after a phase-in period, insulating links must be tested and approved by a Nationally Recognized Testing Laboratory to a test standard developed by a US-based standards development organization.
Accidents involving contact between a power line and a crane are invariably extremely serious, often resulting in extensive injury or the death of crane operative(s). In fact, on average 100 contacts occur each year in the US between a crane and a power line, while 20% of all fatalities in the US construction industry are due to cranes touching power lines. Electrocution because of power line contact is sufficient to cause ventricular fibrillation of the heart, often fatal, while the wound caused by the electrical current leaving the body will often remove legs or feet.
Grounding
a crane is not effective, since enough current can still pass through crane operatives to be fatal.
Crane (machine)
A crane is a type of machine, generally equipped with a hoist, wire ropes or chains, and sheaves, that can be used both to lift and lower materials and to move them horizontally. It uses one or more simple machines to create mechanical advantage and thus move loads beyond the normal capability of...
to electrically isolate the load or the crane wire line and superstructure in order to avoid potential undesirable effects of stray electrical energy. Uses include protection of crane operatives from the danger of electrocution
Electrocution
Electrocution is a type of electric shock that, as determined by a stopped heart, can end life. Electrocution is frequently used to refer to any electric shock received but is technically incorrect; the choice of definition varies from dictionary to dictionary...
should the crane come into contact with a power line
Power Line
Power Line is an American political blog, providing news and commentary from a conservative point-of-view. It was originally written by three lawyers who attended Dartmouth College together: John H. Hinderaker, Scott W. Johnson, and Paul Mirengoff...
, the control of currents generated by electromagnetic induction heating in processes such as metal smelting, and isolation of personnel or ordnance from currents generated by radio frequency energy as might be emitted by radio transmission towers. Insulating links are essentially robust insulators which prevent the flow of electricity through cranes or crane loads and into personnel working near the crane, or into other objects or systems which might suffer damage as a result.
History
The dangers of working near overhead power lines, which have no insulation covering their wires, first became apparent with the electrificationElectrification
Electrification originally referred to the build out of the electrical generating and distribution systems which occurred in the United States, England and other countries from the mid 1880's until around 1940 and is in progress in developing countries. This also included the change over from line...
of Western countries in the first half of the twentieth century. As early as 1931 there was a patent for an insulator that could be affixed to a crane’s wire rope or chain in order to prevent electrocution. Such early designs, however, proved unreliable because of their inability to operate safely in all construction crane environments.
By 1965 Federal law
Federal law
Federal law is the body of law created by the federal government of a country. A federal government is formed when a group of political units, such as states or provinces join together in a federation, surrendering their individual sovereignty and many powers to the central government while...
mandated the use of insulating links on cranes in the United States. However, this requirement was lifted in the 1980s after an investigation found that lethal levels of electrical current could pass through the insulating links in use if they were wet and heavily contaminated at the same time. This investigation was sponsered by the crane industry as a defense for lawsuits involving power line contact. It was later proven that the tests were done using a kaolin mixture that is unlikely to be found at any construction site. However, the probability of simultaneous pollution, wetting and contact with the transmission line is rare. The occurance of these three events is less than 10%, in most of the USA. ( Performance Evaluation of insulating links used for worker protection in cranes, Dr. George G. Karady) This meant that insulating links were not widely used because of the crane industries legal liability.
The US Government introduced a new law in 2010 that mandates the use of approved insulating links in certain situations. The new law requires that after a phase-in period, insulating links must be tested and approved by a Nationally Recognized Testing Laboratory to a test standard developed by a US-based standards development organization.
Purpose When Used in Power Line Safety Applications
Insulating links are needed on cranes and tag lines, (guide ropes), to protect against electrical current passing from the power line through the wire rope of the crane and into the personnel working on or near the crane, figure 4. Figure 5 shows the Federal requirements for working close to a power line. The list includes layers of prevention but the only meaningful protection is the insulating link and tag line insulators. Incidents of power line contact are common because of the difficulty the driver of the crane has in distinguishing the thin cable of the power line against the background of the sky.Accidents involving contact between a power line and a crane are invariably extremely serious, often resulting in extensive injury or the death of crane operative(s). In fact, on average 100 contacts occur each year in the US between a crane and a power line, while 20% of all fatalities in the US construction industry are due to cranes touching power lines. Electrocution because of power line contact is sufficient to cause ventricular fibrillation of the heart, often fatal, while the wound caused by the electrical current leaving the body will often remove legs or feet.
Grounding
Ground (electricity)
In electrical engineering, ground or earth may be the reference point in an electrical circuit from which other voltages are measured, or a common return path for electric current, or a direct physical connection to the Earth....
a crane is not effective, since enough current can still pass through crane operatives to be fatal.