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Thread: Arc flash protection procedures with "dead front installed"

  1. #1
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    Arc flash protection procedures with "dead front installed"

    I have searched the OSHA website for information pertaining to the following question. Are "arc flash" protection procedures required at a 120/208 volt or 277/480 volt panelboard with the "outer panel cover" (granting access to the back box) removed but the "dead front cover" (protecting live parts, buss and lugs) is in place? Please advise whether "arc flash" procedures are required or where I might find this information.

  2. #2
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    if no live voltage is accessible, why would there be an arc flash hazard in the first place?
    Bob

  3. #3
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    I think PPE is required whenever you are working on or near energized equipment.
    If the cover is removed, there is lots of space around the dead front cover, where components of and arc flash and arc blast are easily sent onto the worker.
    IMO PPE is required even if you are working on (maybe operating a CB open/closed or racking a CB in/out) an enclosure that has louvers in the cubicle door.
    Ron

  4. #4
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    You can find info in NFPA 70E.
    Instructor, Industry Advocate

  5. #5
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    NEC 110.16 tells me that the Arc Flash warning should be on the exteriormost cover of just about all electrical enclosures excluding the obvious such as devices and j-boxes. Yes NFPA 70E

  6. #6
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    NFPA 70e is the short answer. Determining arc flash PPE, and when it's required can be difficult. Historically, you and I, and everyone else in the trade, would open 480v distrbution panels without a second thought, in the process subjecting ourselves to arc flash potential. To my knowlege, OSHA has not yet put effective teeth into NFPA 70e. Meaning, it's a good idea to protect yourself, but in most places there are no penalties. Someone please tell me if I am wrong. However, as a supervisor, I require my workers to wear appropriate PPE; including rated shirts, glasses, etc. when exposed to an arc potential. To me it's not worth the risk.

    A label that states an 'arc flash hazard is present' is required, but what needs to be required is a label that states the hazard level. This is measured in the 'energy/calories per centimeter squared' that can be released. When you have this number you can look at the PPE table and it shows what level of PPE is 'required' to protect the worker. Mind you, protect in this case means that you survive. Second and third degree burns are considered acceptable in some sense. Determining the energy released is the result a rather complicated formula which includes distance from the arc, the amount of time it takes to trip the OPCD and available fault current. Even the most sophisticated computer programs used to determine these values are subject to intangibles. Fault current can be the most difficult to determine. Wire length (resistance) affects the value greatly, and who know the exact length of wiring that's been installed for years? OCPD trip time is essential, as is the type and rating of the OCPD. You would think that the further from the utility would be the safest. But if you have a large motor load on a circuit there can be a greater potential of arc flash for several cycles. The further away the OPCD the longer the trip time, etc, etc.

    Arc flash protection and NFPA 70e are in their infancy. I believe we'll be seeing much more about this in the years to come, and we'll be required to provide protection-subject to fines through OSHA at some point. It not yet clear what path that will take or how long.
    chuck mccarty
    electrical supervisor
    bremer electric
    milwaukie, oregon

  7. #7
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    Quote Originally Posted by petersonra
    if no live voltage is accessible, why would there be an arc flash hazard in the first place?
    I have seen the end result of an arc flash incident. The equipment that failed was mounted inside a NEMA cabinet. The cabinet had a 1 foot diameter hole burnt thru it. Thanks be to God there was no one in the vicinity when this happened. That is why there is an arc flash hazard, even if no live voltage is accessible.

  8. #8
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    Quote Originally Posted by pwest
    Are "arc flash" protection procedures required at a 120/208 volt or 277/480 volt panelboard with the "outer panel cover" (granting access to the back box) removed but the "dead front cover" (protecting live parts, buss and lugs) is in place? .
    Probably.

    Chuck laid it out th this arc flash stuff is in the infancy. OSHA was no help to you because it only says that the worker must be protected from hazards on the job. If you have a plan that will protect your employees, you do not need 70E. Arc flashes are extremely unpredictable from case to case.

    If you are like most places, you do not have an original plan for protecting workers and if there was an accident OSHA will ask you why you did not follow 70E. Gotcha. Get out the checkbook.

    Back to your question- the dead front does not protect from the arc reaching the employee if a fish tape is ran into the live buss while he has his finger over a different conduit. Depending on the available fault current, the flash could extend anywhere from a few inches to several feet out into the room. With enough energy, even the outside cover could become a projectile causing injury.

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