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Arc Flash Protection Boundary for 120V

Discussion in 'Electrical Safety Practices' started by George, Sep 22, 2011.

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  1. George Sparks Level

    The more I study 70E in detail, the more questions I have. Our energized work permit requires that the arc flash protection boundary be specified. Energized work at or above 50V requires the EEW permit. In the vast majority of cases, 120V circuits fall under the exemption of 130.3 and as such do not require a calculated calorie value. Then 130.3(A)(1) clearly states that "In those cases where detailed arc flash hazard analysis calculations are not performed for systems that are between 50 volts and 600 volts, the Arc Flash Protection Boundary shall be 4.0 ft." Is everyone else really barricading out to 4 feet to say land a #14 AWG under a terminal going to a limit switch in the field? I have read the debate among those who argue whether 208V will or will not support an arc. If there is that much debate at 208V isn't it pretty clear cut that at 120V an arc will not be sustained? I've been told that is the primary reason 120V was selected for residential in the first place. i.e. It won't sustain an arc. If I am forced to go forward telling our electricians that at 120V the arc flash boundary is 4 feet, I will loose all credibility with them. I'm sure that in their work history a few of them have unfortunately shorted out enough 120V to know better. They will think I am an idiot, and at that point, I guess I will have provided them with the physical evidence to prove they are correct.
  2. Zog Sparks Level

    Why is it an issue?, should not be landing wires energized anyways.
  3. George Sparks Level

    It's not that uncommon for a designer/engineer to run one or two 20A circuits to a field junction box in a manufacturing plant, and then loop power down to a group of terminals to provide take offs to individual instruments. This is fine for the initial build, but when you have to add an instrument years later you must either require that the plant come down or land one conductor energized. It can cost some chemical plants $100,000 plus to come down. You will say nothing is more important than safety and to that I will agree with you 100%. The problem that I have is that in my mind, between gloves and insulated tools I feel it is not unsafe. i.e. I feel very much more exposed driving the Houston freeways to work. Add to that if everything went totally wrong, my belief is that the shock hazard is minimal and the arc flash potential is minimal to non-existant as well.
  4. JBD Sparks Level

    If you are not performing a study, you must be using the 'Task Tables'. In 70E-2012 there are specific boundaries established for each task, rather than the generic 4'. For <240V tasks the new AF boundary is 19".
  5. Zog Sparks Level

    Good point, there are a lot of labels out there that need revisions.
  6. viper57 Sparks Level

    EEWP & Labels

    The EEWP should specify why the system is being "repaired" while energized and a person in authority must request said work and justify in accordance with 130.2(A)... greater hazard or infeasibility.

    Labels applied prior to September 30, 2011 are acceptable if they contain the available IE or required PPE level.
  7. jcampbell Junior Level

    I agree with Vipers point, this electrical work can be done while denergized (in George's example it is costly or inconvenient to power the chemical plant down to perform this work but not infeasible). As a former OSHA compliance officer, I have been on fatality inspections where companies used this "infeasible" situation to try and explain why they did the steps they chose to perform. OSHA, 100% of the time does not see this situation as infeasible. All of the fines put together for all fatality inspections were well over $100,000 each time.
  8. George Sparks Level

    Thanks J Campbell, at the very least I can use your note to push for deenergizing; however, in light of the OSHA action you have referenced how should we take the Informational Note No. 2 on page 70E-22 of the 2012 70E? "...and work on circuits that form an integral part of a continuous process that would otherwise need to be completely shut down in order to permit work on one circuit or piece of equipment." As I interpret this, this is exactly what I was referring to in my original example. I understand that the fine print notes are informational only, but the people controlling the money read this material also. Am I misinterpreting, or is this fine print note totally wrong from OSHA's viewpoint?

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