Earth Ground Collectors, Meet NEC Grounding RequirementsJuly 27, 2019
“All exposed non-current carrying metal parts of cranes, monorail hoists, hoists, and accessories, including pendant controls. Shall be bonded either by mechanical connections or bonding jumpers, where applicable, so that the entire crane or hoist is a ground-fault current path as required or permitted by Article 250, Parts V and VII.
Moving parts, other than removable accessories, or attachments that have metal-to-metal bearing surfaces, shall be considered to be electrically connected to each other through bearing surfaces for grounding purposes. The trolley frame and bridge frame shall not be considered as electrically grounded through the bridge and trolley wheels and its respective tracks. A separate bonding conductor shall be provided.
These requirements are not intended to allow the trolley frame or bridge frame to serve as the EGC for electrical equipment on a crane. The EGCs that are run with the circuit conductors are required to be one of the types described in 250.118. Metal-to-metal bearing surfaces of moving parts are considered to be a suitable grounding and bonding connection. However, the bridge and trolley wheel contact with their tracks is not permitted to be used as a reliable grounding and bonding connection. Because dirt or other foreign surfaces could impede the effectiveness of the wheel-to-track contact as a reliable grounding and bonding connection, the bridge and trolley frames of an electric crane are required to be bonded through the use of a separate conductor.”
Question 1: With respect to electrically operated overhead cranes and hoists. Does OSHA require the equipment to have a connection to ground, via separate equipment grounding conductor and prohibit the path to ground from going through the wheel bearings lubrication, and the wheel-to-rail contact surface?
Response: OSHA’s standard does not specify this requirement. However, the crane equipment you discuss in your request travels on wheels in contact with supporting rails. Where a separate conductor rail is not provided as the low-impedance path for ground-fault current, the grounding path for the crane equipment, whether through the wheel bearings and lubrication and through the wheel-to-rail contact surface or otherwise, must meet the requirements of OSHA’s standards. OSHA requires the frames and tracks of electrically operated cranes and hoists to be grounded such that “[t]he path to ground from circuits, equipment, and enclosures shall be permanent, continuous, and effective.” 29 CFR 1910.304(g)(5) and (g)(7).
Therefore, to the extent that the employer ensures that the path to ground through the wheel will be “permanent, continuous, and effective,” the employer may ground the crane through the wheels. However, OSHA notes that there are a number of substances that could be initially present, or develop through usage, that could be potentially prevent the ground path through the wheels from being “permanent, continuous, and effective.” These insulating materials include, but are limited to, paint, rust, dirt accumulation, and even animal nests and carcasses. OSHA further cautions employers that the most recent editions of the National Electrical Code (NEC) (2005, 2008, and 2011) include a general prohibition on equipment through the bridge and trolley wheels.
Question 2: Does OSHA have any grandfather-type exceptions regarding the grounding requirements for overhead cranes and hoists?
Response: No. Although there is a grandfather provision in 29 CFR 1910.179(b)(2), it applies to the design of overhead and gantry crane equipment and not to how that equipment is installed and c01mected at a facility. According to 29 CFR 1910.179(g)(l)(i), all crane installations must comply with 29 CFR Part 1910 SubpartS, which contains grounding requirements in §§1910.304(g)(5) and (g)(7). Existing crane equipment is not grandfathered (excepted) from these requirements based on the date the equipment was designed or installed. See § 1910.302(b)(1) (“The following requirements apply to all electrical installations and utilization equipment, regardless of when they were designed or installed:*** §1910.304(g)(5)-Grounding-Grounding path … § 191 0.3 04(g)(7)- Grounding-Non Electrical equipment.”).
Question 3: In crane applications, can a separate grounded conductor (neutral) or an equipment grounding conductor be the same color as the other conductors (e.g., can all conductors including the grounded and equipment grounding conductors be red)?
Response: No. As previously stated, 29 CFR 1910.179(g)(1)(i) requires crane installations to comply with 29 CFR 1910. Subpart S. In Subpart S, OSHA has two separate provisions, 29 CFR 1910.304(a)(1)(i) and (a)(ii), which requires that a grounded conductor and an equipment grounding conductor, respectively, must each be identifiable and distinguishable from all other conductors. In general, as noted in the NEC at 200.6 and 250.119, grounded conductors are white or natural gray in color or markings, and equipment grounding conductors are bare (uninsulated) or are green in color or marking. Additionally, in light of your inquiry addressed in Question 2, older installations are not grandfathered from the requirements of CFR 1910.304(a)(1)(i) and (a)(1)(ii).
Thank you for your interest in occupational safety and health. We hope you find this information helpful. OSHA requirements are set by statute, standards, and regulations.
Our interpretation letters explain the requirements, how they apply to particular circumstances, but they cannot create additional employer obligations. This letter constitutes OSHA’s interpretation of the requirements discussed. Note that our enforcement guidance may be affected bt changes to OSHA rules. In addition, from time to time we update our guidance in response to new information. To keep apprised of such developments, you can consult OSHA’s website at http://www.osha.gov. If you have any questions, please feel free to contact the Office of General Industry Enforcement at (202)693-1850.
Thomas Galassi, Director
Directorate of Enforcement Programs
Sizes start at 30LB ASME Rail