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Thread: NFPA 70E Table 130.7(C)(15)(a)

  1. #1
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    NFPA 70E Table 130.7(C)(15)(a)

    Good Day,

    My company is in the process of having an arc flash study performed for the facility. However, in the meantime, we were hoping that Table 130.7(C)(15)(a) could be used as a guide for work on energized equipment until the study is completed. However, I would like some clarification of parameters described in the table, to be more specific, "Potential arc flash boundary with exposed energized conductors or circuit parts". What exactly is considered an exposed energized conductors and circuit parts? Are termination points considered as exposed? What about the insulated conductors i.e. not bare? Is it possible that based on the construction of some switchgear that there are no exposed conductors/circuit parts and as such this parameter is not applicable? We have Cutler Hammer Freedom 2100, Cutler Hammer Ampgard Medium Voltage Starters and the 15kV Metal Clad switchgear from Cutler Hammer. Finally, has anyone used this table in that way? i.e. in lieu of a study. If so, any advice? Besides the exposed conductors in the parameters, some of the short circuit current values and clearing times quoted vary from what we have on our facility.

  2. #2
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    You can use the table but be sure you are compliant with the notes at the bottom of the table.

    There is judgment involved but many think anything not insulated requires PPE.
    Ron

  3. #3
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    Quote Originally Posted by Shells View Post
    Good Day,

    My company is in the process of having an arc flash study performed for the facility. However, in the meantime, we were hoping that Table 130.7(C)(15)(a) could be used as a guide for work on energized equipment until the study is completed. However, I would like some clarification of parameters described in the table, to be more specific, "Potential arc flash boundary with exposed energized conductors or circuit parts". What exactly is considered an exposed energized conductors and circuit parts? Are termination points considered as exposed? What about the insulated conductors i.e. not bare? Is it possible that based on the construction of some switchgear that there are no exposed conductors/circuit parts and as such this parameter is not applicable? We have Cutler Hammer Freedom 2100, Cutler Hammer Ampgard Medium Voltage Starters and the 15kV Metal Clad switchgear from Cutler Hammer. Finally, has anyone used this table in that way? i.e. in lieu of a study. If so, any advice? Besides the exposed conductors in the parameters, some of the short circuit current values and clearing times quoted vary from what we have on our facility.
    Well the goal of the 70E is to not work on enegized equipment, not to be used as a guide to do energized work. So what types of energized work are you talking about? You will notice in the tables racking of breakers is a HRC 4, regardless of the doors being open or closed. Same goes with several other tasks, you do not need to have a bare energized conductor to have an arc flash hazard.

    Also as Ron pointed out, you have to ensure your system falls within the limits stated in the tables.

  4. #4
    Join Date
    Apr 2008
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    Thanks guys, Well the live work being referred to as basically racking in and out of breakers, troubleshooting (voltage measurement etc) and operating the breakers. We really don't do anything live unless we have too. I know we have to make sure that the parameters are the same. I guess what was confusing to me was the definition of exposed conductors and live parts. In the switchgears we have I really cant think of any conductors or parts that are not insulated. Although I have not seen any, the technicians have said that in their experience on other facilities there are switchgears that have bare exposed parts but ours are not like that so they feel the table is too conservative. I guess without an actual study, we need to be conservative regardless.

  5. #5
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    Even after the study, you will need to make internal policies how to apply the study. The study will likely not tell you how to interpret exposed energized conductors. Some folks feel that even if you are operating a pistol grip open/close operator with the cubicle door closed the operator is still exposed to energized conductors as the door is not designed to withstand an arc blast (except arc resistant swgr). The operating parameters within the detail definition are for each employer to interpret.
    Ron

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