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 Post subject: 70E Revision
PostPosted: Thu Jan 21, 2010 5:43 pm 
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http://www.nfpa.org/assets/files/PDF/CodesStandards/TIAErrataFI/ProposedTIA981NFPA70E.pdf Thoughts??


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PostPosted: Fri Jan 22, 2010 6:36 am 
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See [url="http://www.arcflashforum.com/showthread.php?t=861"]this other thread[/url] about that same TIA.


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PostPosted: Sat Jan 23, 2010 10:12 pm 
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Not much of what NFPA is saying is new. In fact, most of it was word for word from the original 2002 IEEE 1584.

IEEE acknowledged that faults could be sustained at 208V and have caused injuries with very 'high' fault current. Small meter enclosures were sighted.

IEEE still concluded that the arc-flash hazard need only be considered for large 208 V systems: systems fed by transformers smaller than 125 kVA should not be a concern. IEEE does not state an impedance value, but I would guess they are assuming industry norms.

NFPA does not provide a method of analysis but states methods are developing and available. The consensus has been IEEE 1584.

So my question is, if NFPA text continues to says to use an analysis method, and you use IEEE 1584, isn't the exemption technically still allowed until IEEE changes their position. 70E 130 is not a method of analysis for determining IE, but 1584 is.

I know I am pushing the point, but I know of a lot of facilities that have employed this exception. The question is going to come up.

Since this whole exception was based on the premise of limited fault current, ie IEEE, why didn't NFPA just specify a fault current level and actually do something helpful.

Can we discuss this some.


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PostPosted: Tue Jan 26, 2010 11:45 am 
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I will continue to use the IEEE exception even if 70E drops it, at least for a time. I am performing arc flash surveys on all of my company’s manufacturing plants. I am about 2/3 complete. It is more important that I spend my time surveying devices that are likely to result in an arc flash if something goes wrong (devices that are not included in the exception). The way I understand it, it is possible, but not likely, for a 208 volt device fed from a single transformer <125 kVA to sustain an arc flash. I will add another disclaimer to my reports stating that an arc flash is possible on such devices. I can always go back and add the 208 volt devices to the surveys at a later point, such as during the required periodic reviews.

Instead of eliminating the exception, we need to figure out an appropriate stopping point. If a <240 volt device fed by a single <125 kVA transformer is not the appropriate stopping point, what is? Is it really necessary to survey down to a servo panel which is fed by a 480:80 volt, 3 phase, 30 kVA transformer for example? Surely there is a cut-off that can be established…fault current less than 10kA? 5kA? 2kA? or a combination of low voltage and low fault current?

Simply eliminating the exception is not the right answer. Determining the appropriate stopping point is the right answer.


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PostPosted: Tue Jan 26, 2010 8:56 pm 
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Amen brother, but thats not what NFPA did. I keep getting the impression that arc flash is going to be a 30 year money maker with no end in sight. NFPA appears to want to make this 'fool proof'. I instead, would look to make it 'highly unlikely'. The IEEE cutoff sounded like a good point to me to stop. If I had to pick an alternate, I would then say 10KAIC rated panelboards.

The problem that the NFPA created, and they must obviously know that they 'created' a problem, is that Art 130 implies that there are several 'analysis' methods and that any can be determined to calculate IE. So since the most common method, IEEE 1584, says that calculation at or below 208 & 125KVA is not required. So you rightly follow Art 130 by adhering to 1584. But, now you have NFPA explicitly declaring that this portion of 1584 is 'wrong'.

This is almost comical.

Since Art 130 is not an OSHA requirement, and that establishment of a program in compliance of 130 meets the obligation of the General Duty Clause, I would say that continuing to follow the 1584 exception would not violate that condition. There are several vague and non-specific requirements which require interpretation by the establishing owner.

This exception gave us a ending point that made sense. Without something similar you'd be force to analyze ever component down to 50V. That seems unreasonalbe.

Still, its going to be risky to just ignore the TIA.


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PostPosted: Wed Jan 27, 2010 12:39 pm 
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haze10 wrote:
This exception gave us a ending point that made sense. Without something similar you'd be force to analyze ever component down to 50V. That seems unreasonalbe.



Absolutely seems unreasonable.

haze10 wrote:
Still, its going to be risky to just ignore the TIA.


Ignore is not the right word. I will spend my time for the next two years surveying the equipment in our plants that are more likely to experience an arc flash. After I complete the survey for this equipment, I can then come back and include the lower likelihood equipment (items currently covered by the exemption). This way my people are protected from the higher risk equipment quicker. Priority goes to the higher risk equipment. In the mean time a disclaimer would let the people know that an arc flash hazard still exists on the lower voltage equipment.

I am an employee of the industrial company for who these arc flash surveys are done. This would tougher to do for an engineering firm. An engineering firm would probably have to include everything upfront.


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PostPosted: Wed Jan 27, 2010 1:26 pm 
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JJH wrote:
In the mean time a disclaimer would let the people know that an arc flash hazard still exists on the lower voltage equipment.


NEC article 110.16 requires (for a whole bunch of electrical equipment) such a label.


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PostPosted: Wed Jan 27, 2010 2:13 pm 
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I guess it is my turn to stir things up....

......again! :cool:


I have simple question:

How many people that visit this forum have actually had:

a significant arc flash (lab experiments don't count) from a 208 or 240 volt circuit downstream from a smaller transformer like 112.5 kVA or less

or

know someone who has seen this event?

I am curious to hear everyone's experiences with the low voltage arc flash.

_________________
Jim Phillips, P.E.
Brainfiller.com


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