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Thursday, February 23, 2017
Question:
In the crane world when it comes to exposed bussbar, section 12.3.3 talks about unqualified persons and a limited approach area. When it comes to this, does the 10 ft rule/approach restriction apply to open bussbar for unqualified individuals?
Derek Johnson
A
Answer:
Hey Derek thanks for your question. Runway contact conductors must be guarded as stated in 610.21 so that people cannot inadvertently touch energized parts. Guarding of live parts 50 volts and higher is covered in 110.27 and elevation is one specific method that is allowed.
I found Section 12.3.3 in a Reclamation Safety and Health Standard and do not know if that is the specific standard you are referring to but the wording is similar to that in NFPA 70E -2015.
In general an unqualified person must stay out of the limited approach boundary as stated in 130.4(C)(1) of NFPA 70E. Table 130.4(D)(a) gives a 10 foot limited approach boundary for exposed movable conductors up to 72.5 kV. Superscript note "c" to that table provides some guidance regarding what a movable conductor is. For exposed fixed circuit parts the dimension is 3 ft 6 inches up to 750 volts.
So if the exposed energized parts are movable, such as crane contact conductors, it would make sense for the employers work practices and procedures to require unqualified persons stay at least 10 feet from the exposed conductors under the conditions stated.