Author: Marc-André Martineau
Manager & Partner at Premium Industrial Group
Do you have several overhead cranes sharing the same crane runway?
Would you like to ensure the safety of your maintenance interventions while keeping your operations running?
In this article, we'll show you how to create a safe maintenance zone to avoid unnecessary downtime and the risk of electric shock.
We will look at what a maintenance zone is, the benefits it can bring to your plant, the risks to consider, and the budget to plan for.
What is an overhead crane maintenance area?
It is a section of the runway that can be reserved to carry out maintenance work at the desired time. Also called an isolation zone, this section is intended to prevent other overhead cranes using the same runway from entering it. How does it work?
When the adjacent overhead crane approaches the zone, it ceases to be powered and stops itself. In this way, the technician can carry out maintenance on the lifting device in complete safety, while the other cranes continue to operate.
In general, this zone is located at the ends of the track, since this configuration is less costly. But it could be positioned anywhere along the track.
The length of the section can also vary according to your needs, for example, depending on the number of overhead cranes you wish to park there during maintenance. However, its length must take into account the deceleration distance of adjacent overhead cranes.
Note that these systems are designed for indoor use only.
What are the advantages of the maintenance zone?
Normally, when maintenance is required on overhead cranes, the power supply has to be disconnected. However, when there are several overhead cranes on the same runway track, the power will be cut off to all the lifting devices. The maintenance zone makes it possible to cut power to only a portion of the track, by means of an electrical panel located between the power isolator and the conductor bars. Depending on your situation, this solution can offer the following benefits:
- Productivity: Maintenance of your critical overhead cranes can be carried out without stopping your operations
- Cost savings: Your maintenance zone can help you save money by avoiding the more expensive intervention of a technician outside normal working hours!
- Safety: This solution could even be used to secure a section for work at height other than overhead crane maintenance. This could involve a variety of recurring tasks in an area crossed by the track (garage door system, light fixtures, heating system, etc). A true maintenance zone is safer from the risk of collision or electrocution.
Application example
This type of technology can be useful in many industries. But let's take the example of a steel distribution company with 5 overhead cranes on a 760 ft. track. It might decide to install 1 maintenance area at each end. Why would this be appropriate? In this type of industry, overhead cranes can be heavily used. They are often the main working tool for handling beams and for loading and unloading, with no other alternative.
So any industry where lifting equipment is central to productivity could benefit from evaluating the option of a maintenance zone.
Let's now take a closer look at the safety matter.
Isolation zone and overhead crane maintenance: what are the risks?
Hazard No. 1: electrical continuity
A poorly designed isolation zone can create a false sense of security. When it is not built according to proper electrical practices, it may allow electrical continuity to remain even though the power is presumed to be disconnected. This is the type of risk highlighted by the Government of Ontario following an accident that caused the death of a worker performing maintenance on an overhead crane. To understand, let's first look at how overhead cranes are electrified.
Electric current is transmitted to the overhead crane by conductor bars energized along their entire length. To ensure that this current reaches the equipment as it travels, it is collected by blades attached to the crane, which slide along the bar as it travels. These are known as collector shoes.
Theoretically, when these blades reach the padlocked section, they will be de-energized and the machine will stop. But in reality, and particularly when using a double shoe (two collector shoes following each other), the collector shoe system can itself transmit electrical current to the padlocked area! But how?
If half the collector assembly has crossed the zero energy line, the other half is still in a powered section. As electricity is in constant movement, the area that should be current-free receives current from the part of the collector that is still energized (electrical conduction). The area supposed to be powerless is therefore energized at this precise moment. It's then necessary to wait until all the blades have moved to the 0-energy side before the current dissipates and no longer poses a danger.
Hence the importance of the buffer zone. This small section between the zero-energy zone and the energized zone serves as a transition to prevent electrical conduction. Without this crucial section, a technician working on an electrical component runs the risk of being electrocuted, even if he or she is in the maintenance zone.
Hazard No. 2: positioning of the overhead crane during maintenance
As we saw earlier in this article, the length of the zone must take into account the deceleration distance of adjacent overhead cranes in order to prevent any contact with the overhead crane under maintenance.
Proper signage is therefore necessary to ensure a safe maintenance zone. Even though this may seem simple, it is important to clearly indicate to maintenance technicians where this protected section is located. Visible signage, such as signs posted along the runway, must clearly identify where the maintenance zone begins and ends.
If the deceleration distance is not sufficient to prevent contact, the installation of temporary end stop should be planned.
Can true 0-energy be achieved simply with remote control management?Some people think that when the operator cuts off the power supply using the emergency stop function on the remote control, and that the remote control is carefully secured, it can be assumed that the intervention will be 0-energy. But in reality, this is not the case. For more information, see the box "What is a 0-energy overhead crane?" in the article "Working at height: Can an overhead crane be used to lift a worker or protect him from falling?" |
What is the cost of a maintenance zone for an overhead crane?
The cost of a maintenance zone generally ranges from $7,000 to $15,000 in materials. This amount varies depending on the total amperage of all overhead cranes operating on the same runway.
The installation of power disconnect conductor bars, a lockable isolation panel, and the wiring required for the connection must also be planned for. While the conductor bars can usually be installed by most overhead crane manufacturers, the connection between the conductor bars and the isolation panel must be carried out by a licensed electrician. It is therefore important to include this budget in the planning of your maintenance zone.
Talk to a specialist about feasibility at your plant
As you've seen, a safe maintenance zone guarantees true zero energy, reduces the risk of electric shock, and optimizes your maintenance interventions without interrupting your operations.
Would you like to know whether this type of installation is realistic in your industrial environment?
Our specialists can analyze your installations, design a zone tailored to your requirements, and assist you with its implementation.
You can contact one of our experts by clicking on the button at the bottom of this page. They will be able to help you assess the viability of your project and assist you in its realization.
