Crane Power Grounding – 3 Bars are Not Enough
IT IS SHOCKING HOW MANY IMPROPERLY GROUNDED CRANE SYSTEMS ARE STILL IN SERVICE!
Would you ever consider installing a high voltage piece of equipment that without a proper ground to protect workers from potentially fatal electrical shock? At CRANE 1, we would never allow it, but every single day our inspectors and technicians encounter an elementary electrical safety issue with cranes and hoists in the field that has been overlooked in prior safety/compliance inspections or knowingly ignored by the designated person responsible for crane safety at the site.
Many incorrectly think that improperly installed crane electrification without a dedicated ground is “OK” since it is “grounded” to the structure. or that the unsafe installations are somehow “grandfathered” by OSHA. OSHA requires that the crane or hoist ground be permanent, continuous and effective.
This misguided thinking absolutely exposes workers using the crane and touching the hook or other conductive parts of the crane or hoist to a potentially fatal shock whenever the improper ground fails due to debris on the runway or any of a number of other causes. We routinely respond to customers saying their crane shocked their worker, only to find that there is no dedicated ground.
Just think that these systems, without a dedicated ground, rely on a permanent, continuous and effective ground through the trolley wheel bearings through the crane structure through the crane wheel bearings and likely a dirty running surface of the runway and then into the runway structure which is not even properly bonded to the building ground. That’s a lot of potential for grounding failures.
OSHA has required that cranes be properly grounded by decades and the NEC provided updated grounding requirements in the 2005 revised edition of ANSI/NFPA 70 National Electric Code within Article 610, Cranes and Hoists, Section 610.61 Grounding. Within the text of the section, it clearly states: “The trolley frame and bridge frame shall not be considered electrically grounded through the bridge and trolley wheels and its respective tracks. A separate bonding conductor shall be provided.” The terms “ shall and shall not ” clearly make the use of a dedicated fourth conductor for ground mandatory. It does not matter if the electrification is festoon cable or insulated conductor bar.
THE EASY SOLUTION:
CRANE 1 Inspectors or Field Service Technicians or Field Consultants can review your existing system and in most cases, we can simply add a fourth bar and additional collectors to your equipment. Retrofit extension brackets are mad if the electrification bracket is too short to add a fourth bar. We will connect the ground to your power junction box to an existing bonded ground. If a proper ground is not present in the junction, the ground will need to be pulled from the disconnect box.
OSHA INTERPRETATION REGARDING GROUNDING CONDUCTORS
Electrical Grounding of Overhead Cranes and Hoists.
Standard Number: 1910.179 Standard Interpretations
https://www.osha.gov/laws-regs/standardinterpretations/2011-12-05
You asked questions about OSHA’s general industry requirements for grounding overhead cranes and hoists. This letter constitutes OSHA’s interpretation only of the requirements discussed and may not be applicable to any question not delineated within our original correspondence. Your paraphrased scenarios and questions and our replies follow.
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).[1] 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.[2]
Response: No. Although there is a grandfather provision in 29 CFR 1910.179(b)(2),[3] it applies to the design of overhead and gantry crane equipment and not to how that equipment is installed and connected 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.”).
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.[4 ] 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 by 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. Sincerely, [1] 29 CFR 1910.304(g)(5) requires that “[t]he path to ground from circuits, equipment, and enclosures shall be permanent, continuous, and effective. ” 29 CFR 1910.304(g)(7) includes a requirement, as follows, for the cranes and hoists:” The metal parts of the following nonelectrical equipment shall be grounded: frames and tracks of electrically operated cranes an hoists.” [2] The National Electrical Code, NFPA 70, is available from the National Fire Protection Association, One Batterymarch Park, Quincy, Massachusetts 02169-7471. Article 610-Cranes and Hoists-of the 2005, 2008, and 2011 Editions contains provision 610.61, which requires, in part, that “[t]he trolley frame and bridge frame shall not be considered as electrically grounded through the bridge and trolley wheels and its respective tracks,” and that “[a] separate bonding conductor shall be provided.” [3] 29 CFR 1910.179 is OSHA’s standard for overhead and gantry cranes, including their integral hoists. Paragraph (b)(2) of that standard requires that all new equipment constructed or installed on or after August 31, 1971, must meet the design specifications of the American National Standard Safety Code for Overhead and Gantry Cranes, ANSI B30.2.0-1967. Although this is a grandfather-type provision, it would not apply to the installation requirement [4] Paragraph (a)(1)(i) of 29 CFR 1910.304 requires that “[a] conductor used as a grounded conductor shall be identifiable and distinguishable from all other conductors.” Paragraph (a)(1)(ii) requires that “[a] conductor used as an equipment grounding conductor shall be identifiable and distinguishable from all other conductors.” |
NEC GROUNDING REQUIREMENTS
The grounding requirements are best-outlined verbatim per NEC Article 610, Part VII. 610.61: Grounding. 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, (grounding) 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 bonded 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. The requirements of 610.61 are not intended to allow the trolley or bridge frame to serve as the equipment grounding conductor for electrical equipment (such as motors, motor controllers, lighting devices and transformers) on a crane or monorail. Metal to metal bearing surfaces of moving parts are considered to be a suitable grounding and bonding connection. (As in collectors on conductor systems, hard-wired festoon grounding, etc.)
The bridge and trolley wheel contact with their tracks is not permitted to be used as a reliable grounding and bonding connection. Due to dirt or other foreign surfaces impeding 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 now required to be bonded through the use of a separate conductor.
