Alert: Collector shoe assemblies on overhead cranes - bridging an isolation gap
Learn about the rules and regulations to reduce risk of injury or death when working with collector shoe assemblies on overhead cranes.
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A crane service company technician (the worker) was completing preventative maintenance work on an overhead crane. There were two cranes operating in the same crane way. The employer had moved the crane that was being maintained to a position where they were able to shut off and lock out the electrical power to the bus bars in an isolated section at one end of the crane way. The second crane continued to operate while the repairs to the other were completed.
Each of the two cranes was equipped with a double arm collector shoe assembly that made contact with the bus bars and provided power to the cranes. Each of these collector shoe assemblies had a total of six collector shoes with inserts and two shoes and double arms on each bus bar that provided for a steady flow of electricity to the cranes’ motors. Each collector shoe assembly has a set consisting of three phases of shoes, or a leading set, termed the first set; and a set consisting of three phases of shoes, or a trailing set, termed the second set. The designation of leading and trailing sets changes depending on the direction of travel, as each crane is able to travel in both directions along the crane way.
To create the isolation section, an isolation gap was created between the bus bars in the crane way so that the current from the main section bus bars was prevented from reaching the bus bars in the section to be isolated. The electrical power at the isolation gap was diverted through a disconnect and routed back to the section of the bus bar that needed to be isolated. With the disconnect locked open, the bus bars in the isolation section were de-energized.
The worker was changing a worn insert in one of the shoes in the double arm collector shoe assembly (which had been de-energized) when he was fatally injured by electrical contact due to the subsequent, inadvertent energization of the isolated section of the bus bars he was working on. This inadvertent energization caused by current bridging the isolation gap is due to the inherent design and construction of the double arm collector shoe assembly.
If there are multiple cranes in a crane way and they are equipped with double arm collector shoe assemblies, there is a danger that the double arm collector shoe assembly from the operating crane can create a bridge between the energized main bus bar section and the isolated section.
This condition had occurred when the operating crane was moved into a position where second set of shoes for the double arm collector shoe assembly was in contact with the main bus bar, and the first set of shoes for the double arm collector shoe assembly came into contact with the isolation section, thus bridging the isolation gap. The design and construction of the double arm collector shoe assembly is such that the first set of shoes is electrically connected to the second set of shoes at all times.
In general, there is a hazard when there are two cranes sharing the same crane way (and the operating crane has a double arm collector assembly), when the second crane is allowed to operate (remain energized) and, this crane’s first set of collector shoes encroaches into the isolation section while its second set of collector shoes remains in the energized main section. This results in current bridging the isolation gap, despite the first crane having been placed in the isolated (de-energized) section.
A worker performing work on the first, stationary crane’s double arm collector shoe assembly on the initially de-energized section could then inadvertently, come into contact with subsequently energized electrical parts that he or she believes had been safely de-energized. This hazard is due to the isolation section becoming energized from the operation and encroachment of the second, operating crane into the isolated section.
Locations and sectors
Any facility that operates two or more overhead cranes in the same crane way. This could include steel plants, heavy equipment production or assemblies, large parts machining facilities, steel slitting plants, heavy parts processing and materials handling facilities.
Section 42 of Regulation 851 requires that when electrical maintenance work is carried out on a crane, the power supply must be disconnected, locked out of service and tagged before any work is performed. However, if there are multiple cranes operating on the same crane way additional precautions may be required. If the multiple crane way is equipped with a double arm shoe collector shoe assembly then the power supply to the full crane way must be disconnected, locked out of service and tagged before any work is performed.
Section 42 of the Regulation for Industrial Establishments (Regulation 851):
- Subsection 42(1) — The power supply to electrical installations, equipment or conductors must be disconnected, locked out of service and tagged before any work is done and while it is being done, and
- Subsection 42(7) — The employer must write and implement procedures for being in compliance with this section.
Under Section 25 of the Occupational Health and Safety Act (OHSA), the employer must:
- Clause 25(2)(h) — take every precaution reasonable in the circumstances to protect workers,
- Clause 25(2)(a) — provide information, instruction and supervision to protect the health and safety of the worker, and
- Clause 25(2)(c) — ensure the measures and procedures prescribed are carried out in the workplace.
Under Section 27 of the OHSA, the supervisor must:
- Clause 27(1)(a) – ensure that a worker works in a manner and with the protective devices, measures and procedures required by the act and its regulations,
- Clause 27(2)(a) – advise a worker of the existence of any potential or actual danger to the health or safety of the worker of which the supervisor is aware;
- Clause 27(2)(b) – provide a worker with written instructions on the measures and procedures to be taken for the protection of the worker, where so prescribed, and
- Clause 27(2)(c) – take every reasonable precaution in the circumstances for the protection of the worker.
Under Section 28 of the OHSA, a worker must:
- Clause 28(1)(a) - work in compliance with the provisions of the act and its regulations,
- Clause 28(1)(b) - use or wear the equipment, protective devices or clothing that the worker’s employer requires to be used or worn,
- Clause 28(1)(c) - report to their employer or supervisor the absence of or defect in any equipment or protective device and which may endanger them or another worker, and
For more information
This resource does not replace the Occupational Health and Safety Act (OHSA) and its regulations, and should not be used as or considered legal advice. Health and safety inspectors apply and enforce these laws based on the facts they find in the workplace.