Electrocution is one of the most common causes of workplace death for overhead crane operators. According to a recent study from the Center to Protect Workers' Rights (CPWR), half of all electrocutions occurred when a crane boom or cable was brought into contact with an overhead power line.
Safety is paramount when it comes to operating overhead cranes and other lifting equipment, and the importance of keeping this equipment grounded can't be overstated. The following takes an in-depth look at grounding requirements for overhead cranes, as well as what workers can do to protect themselves when working on or around overhead cranes.
Why is Grounding So Important?
Proper grounding is an absolute must for crane operators and nearby workers, as it provides an opportunity for electricity to return safely to the ground without posing a danger to others. Keep in mind that electrical current favors the path of least resistance. Without a proper grounding system, the crane operator or anyone unfortunate enough to touch the crane could end up becoming the ground.
It's not just worker safety that makes proper grounding so important. Today's modern overhead cranes are outfitted with the latest in remote monitoring equipment and other assorted electronics. These electronics are also vulnerable to electrocution hazards and require protection against shock.
Common Rules on Grounding Overhead Cranes
The Occupational Safety and Health Administration (OSHA) has several rules governing how overhead cranes and hoists should be grounded. These rules actually incorporate several existing standards set by the American Society of Mechanical Engineers (ASME) and the American National Standards Institute, including the grounding standards found in the National Fire Protection Association (NFPA) Number 70 National Electrical Code. According to these standards:
- Exposed metal components that aren't carrying current must be bonded by bonding jumpers or mechanical connections to create a ground-fault current path.
- An overhead crane's moving parts are considered to be grounded through their bearing surfaces. The exceptions include removable accessories and attachments with metal-to-metal bearing surfaces.
- A separate bonding conductor is required for trolley frames and bridge frames, since they're not considered to be grounded through the bridge and trolley wheels.
OSHA's standards also require the frames and tracks of electrically operated cranes to be grounded. It's also important to note that separate grounded conductors and equipment grounding conductors cannot be the same color as other existing conductors. Instead, grounded conductors should be white or natural gray in color or markings, while equipment grounding conductors can be green in color or marking or, in many cases, left uninsulated.
Three Grounding Bars Aren't Enough
It's not unusual to see older overhead cranes equipped with only three grounding bars, as opposed to the four grounding bars usually seen on newer cranes. However, operating a crane with just three grounding bars in place can expose operators and nearby workers to an unnecessary electrocution risk. Current OSHA regulations also require overhead cranes outfitted with additional electronics to have a fourth grounding bar equipped.
Many owners of older overhead cranes will point to the grandfather provision in 29 CFR 1910.179(b)(2) as their reason for not adding a fourth grounding bar. However, this provision is constantly misinterpreted. Despite referring to the overall design of the overhead crane, the grandfather provision does not touch on how the equipment is installed and connected. As a result, there's nothing that specifically exempts older overhead cranes from current regulations on equipment grounding.
In most cases, retrofitting a fourth grounding bar onto an overhead crane is only a matter of adding the additional bar onto the existing power bar system, along with new collector shoes. Unfortunately, some owners may choose to overlook this requirement due to the costs involved or a poor interpretation of the grandfather provision.
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