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 Post subject: Where does the Arc Flash Boundary Begin?
PostPosted: Thu Oct 27, 2011 11:47 am 
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Joined: Thu Oct 27, 2011 9:34 am
Posts: 14
In 2012, in the definition of an Arc Flash Hazard has two informational notes: 1) is somewhat contradicting saying first that when electrical conductors or circuit parts are within equipment in a guarded or enclosed condition and it is interacted with that it could cause an electric arc. Then it says that under normal conditions this enclosed equipment is not likely to pose an arc flash hazard. 2) then points you to the hazard category tables of activities that could pose an arc flash hazard.
In order for their to be an arc flash hazard recognized by NFPA that requires standards to kick in there has to be an incident energy at some distance of 1.2 cal/cm2. So, from my experience and collaboration with other electrical consultants, if an electrical conductor or circuit part has been calculated to be able to produce at least this much incident energy, then a arc flash boundary needs to be established if the equipment is going to be worked on or a person is going to interact with the equipment. Agree?

If this is the case, then if you review Table 130.7(C)(15)(a) it provides the example of CB operation with covers on below 240 V. This activity requires Cat 0 PPE. Even though Category 0 PPE does not contain any AR PPE, it is still considered to have an Arc Flash Hazard for this activity, at this voltage, because of the requirement for PPE to be donned in order to not receive more than a second degree burn. The 2012 standard sets this arc flash boundary at 19" which means that at 19" a qualified electrician shall don Category 0 PPE before going in and activating/interacting a breaker that is in a box rated at 240 V or below with the covers on? Agree?

On a side note, it has been found that if a detailed analysis is performed in the above example it could bring AFB down to 1"-3". In my experience, in order to not don Cat 0 PPE for activating breakers on panels 240 or below a calculation has to be completed presenting that it is not possible for the panel to introduce 1.2 cal/cm2 incident energy. Agree?


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PostPosted: Fri Oct 28, 2011 9:13 am 
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Joined: Fri Oct 30, 2009 9:20 am
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Location: Texas
I'm a little behind, still operating from the 2009 version of 70E because I have not had time to thoroughly study the 2012, but here is the way I read the standard. If you reach 1.2cal/cm2, you are at HRC 1. I see nothing in the standard to define when you are not at HRC 0. This is unfortunate because it leads to the debates as to where you draw the line. The vast majority of folks will agree that an MCC that calculated to be HRC 0 must be treated as HRC 0 PPE, and then we agree that an office light switch is not treated the same. I agree also, but it doesn't define the division point. So people are going to continue to disagree on the single pole 120V breaker fed from ???KVA transformer etc.


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PostPosted: Fri Oct 28, 2011 10:51 am 
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Joined: Sat May 17, 2008 5:00 pm
Posts: 76
George wrote:
I'm ...the way I read the standard. If you reach 1.2cal/cm2, you are at HRC 1. I see nothing in the standard to define when you are not at HRC 0.


Below 1.2 cal/cm2 is Cat 0.

1.2 cal/cm2 up to 4 cal/cm2 is Cat 1.

You're right, I did not see 1.2 listed in the 2009 Edition of 70E on Table 130.7(C)(11) Only the ususal 4, 8, 25 and 40 cal/cm2 ratings.


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