normal conditions, worker is not exposed to energized parts. Abnormal Conditions. Risk for shock & arc flash increase under abnormal conditions. • NFPA 70E. ISBN: (PDF). IMPORTANT .. The edition of NFPA 70E marked another waypoint as this standard continued to evolve and meet the. 1 — Significant Changes to the NFPA 70E Standard Edition. Peter Walsh, PE The NFPA 70E endeavors to explain in detail how to prevent electrical hazards. The technical .. TT-SCN | PDF | | © Mersen. Amp- Trap.
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The Technical Questions Service is free with your NFPA Membership. Our Technical Questions Service provides a convenient way to receive timely and. NFPA 70E requirements for safe work practices to protect personnel by reducing exposure to major electrical hazards. Originally developed at OSHA's request. NFPA 70E - Standard for Electrical Safety in the Workplace .. Arc Flash Event Use the tables from the NFPA 70E (Recently Updated).
I appreciate the clarifications I didn't know there were 8 different calculation methods I used 2 seconds in my calculations. I guess the moral of the story is that without employing the "exception" a person at this panel could be exposed to a high amount of incident energy based upon my calculations.
And, without employing the exception I would advise wearing a cat. At the end of the day I'm most concerned with worker safety and I want to feel confident in the end results of the analysis. Sun Nov 04, Mon Nov 05, 1: Thu Nov 08, The kVA exception is assuming there is no upstream device i.
Sat Nov 10, Jim, Can you clarify what you mean by "no upstream device"? In other words the only limit on the incident energy is essentially the transformer impedance and the available fault current and voltage.
On another note, I know you had previously discussed going with a minimum level of PPE for all panels in which you apply the exception.
For example, I've heard of people saying that if you have under 5k of fault current on a V system, perhaps you could label everything as a category 2.
This was common at a utility that I worked for previously, long before I was neck-deap in this arc flash hazard stuff. Any thoughts on that? Post subject: Vincent B. Sparks Level. Jim Phillips brainfiller. Plasma Level.
JCV wrote: It will instead refer to IEEE for guidance. I just submitted proposed language for the next edition of My language provides the exception where the short circuit current is 5 kA or less and the voltage is Volts and less.
As far as the AFB above 50V, yes this could cause confusion. There was a suggestion a while back to require Ei calculations down to 50V. The committee had a look of "where did that come from" and everyone quickly chimed in "how would you do it?
Low Voltage Qualified
There are many well intentioned people out there with ideas but sometimes they don't always fit into the big picture of what we know. Thanks for the quick response! Your input is much appreciated. Everyone begins somewhere. It's a pretty amazing field.
The NFPA 70E Electrical Safety The NFPA 70E Electrical Safety Presentation Updated for 2012
NFPA 70E has several methods for the analysis including the hazard risk tables. IEEE is just the calculation method. Either way, according to NFPA 70E, a hazard analysis has to be done for systems not placed in an electrically safe work condition that are greater than 50 volts.
The kVA exception is for systems less than V i. The edition of NFPA 70E had similar language but they mis-copied it and had volts or less instead of less than volts. The problem with the calculation exception is that it does not tell you what to do as far as protection if you do not perform the calculations.
Great question! I asked this question as part of the "Question of the Week" some time back to see how people are handling this. There does not seem to be one answer and many very talented people on the forum have different opinions.
The survey question is at the following link: You do not have the required permissions to view the files attached to this post. Not quite there yet. The annex gives no less than 8 different methods.
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Of those, just one is IEEE And IEEE is the only method that contains the exception you are referring to. So if you are using one of the other methods, then the exception would not apply. It is left up to you as the end user to determine which method you feel is the most valid. In many cases, it isn't. For instance we have 23 kV buses where I work at.
IEEE is not valid above 15 kV. The only calculation given in IEEE for this voltage range is the Lee method and that method is exponentially less accurate as voltage increases.
So strictly speaking it was correct to delete the low voltage exception out of 70E because that is a peculiarity with a particular calculation method. If you use IEEE as the method of choice then at least with the current edition, the exception exists. There is another "exception" in IEEE They acknowledge that beyond 2 seconds, anyone within the vicinity of an arc flash would either attempt to escape on their own or be physically pushed out of the area by the arc blast.
The language within IEEE in this regard isn't that good but almost all engineers cut off the arcing time at 2 seconds. I don't have the parameters used in your calculation but if you used 40 seconds for an opening time instead of 2 seconds, then the incident energy would be 20 times higher than typically calculated.
Mon Jun 07, Meant to say 70E-4 Log 79 should have been accepted in principle and 70E Log should have been as well. Tue Jun 08, 1: Tue Jun 08, 4: Thanks to all the people who actively participate to improve these standards.
What I should have said - What are some of the highlights of the items likely to be accepted that most affect the way we do arc flash studies. In other words what changes might I wish to start incorporating now in my studies looking to the future? I have skimmed through it; hopefully I will be able to find some time soon to read it more thoroughly.
Wed Jun 16, 6: If I understand correctly, the same committee that voted before will take the public comments and then re-vote on the proposals based on those public comments? Also, do all comments have to be on the form provided? Are all of the public comments published in the ROC document or just a selection of them?
Jim Phillips brainfiller.
Post subject: Plasma Level. Sparks Level. Wilson99 wrote: Guidance on DC systems and adding DC to the tables, stricter labeling requirements and some changes to the requirements of arc flash studies, and maintaining them current.
Read the whole thing.Sat Jun 05, 7: Plasma Level. PaulEngr wrote: I have skimmed through it; hopefully I will be able to find some time soon to read it more thoroughly. Jump to: