NFPA 70E Question

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Section 310.6, Portable Tools and Equipment makes reference to "cell line working zones" and grounding. Currently I am on a project that has placed us directly underneath transmission lines. In working with grounding procedures, I am trying to figure out exactly what is the cell line working zone and would it apply to the work we are doing (non electrical) The transmission company safety director is also unclear of this statement. If someone could help me out, it would greatly be appreciated.
 

chris kennedy

Senior Member
Location
Miami Fla.
Occupation
60 yr old tool twisting electrician
Also not sure with how this relates to working under transmission lines, but this may provide some insight into cell line working zones. The highlighted blue area is commentary from the 09 70E handbook.

310.4 Employee Training

(2) Qualified Persons. Qualified persons shall be permitted to work within the cell line working zone.

In electrolytic cell working zones, individual cells normally act as batteries. Direct current voltage is supplied by the cells as well as by rectifying equipment. Because the dc voltage normally is ungrounded, hand tools that might contact the dc bus work must not be grounded. Employees who work within the area of the dc bus must be trained to understand the unique hazards associated with ungrounded dc voltage.

Hazard/risk analyses used for ac circuits might not be appropriate for use with dc circuits. Each employee must be trained to understand how he or she might be exposed to a thermal hazard associated with an arc flash. Employees must understand how to select personal protective equipment (PPE) for use when they exposed to an arcing fault.
 
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