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 Post subject: Intent of Arc Flash Labels
PostPosted: Wed Apr 26, 2017 5:38 pm 
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I have a real problem , my company Electrical Engineer states that Arc Flash Labels only apply to Energized work his definition, working on exposed electrical conductors.

Why is this a problem?

Many of the Switchboards 12,450 volt / 480 volt are labeled Category Dangerous with arc flash approach boundries up to and beyond 30 feet.

Knowing that the protective devices i.e. circuit breakers have not been tested since 1992 and that the switchboards are circa 1966-1982.

EH&S states that they have not yet adopted NFPA 70 E 2015.

Knowing that 35 % of Arc Flash incidents occur without human interaction and that many of the Arc Flash Analysis recommendations identified a multitude of "over dutied " circuit breakers which were never replaced.

Reason given- the reports were wrong.

I have been in the Electrical Industry for 45 years and this line of reasoning reeks of production driven disregard for worker safety.

Being asked to work within or near such equipment and certainly within the category Dangerous Hazard Area makes me question the sanity of some of these decision makers.

The facility has over 250 of these Switchboards which they call substations.

Can someone please provide me with a sanity check?


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 Post subject: Re: Intent of Arc Flash Labels
PostPosted: Sat Apr 29, 2017 10:01 am 
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This seems to be the core of your concern:

Quote:
Knowing that 35 % of Arc Flash incidents occur without human interaction and that many of the Arc Flash Analysis recommendations identified a multitude of "over dutied " circuit breakers which were never replaced.


I don't know where this statistic comes from and you are mixing results. IEEE 499 (Gold Book) or the newer version certainly has statistics on how many faults are arcing faults and that number sounds about right. But it doesn't indicate when they occur. So even though this might be true, it doesn't tell you that most of them probably occur when equipment is changing state, not just sitting there working or idle. So just walking by isn't a significant hazard and the 70E Committee has stated this numerous times. If a human isn't involved these aren't arc flash. Arc flash is a term applied to when humans are exposed to the heat of an arcing fault. So 35% of faults might be arcing faults but only a few of those are arc flashes.

So the entire focus is on addressing those activities where the "spontaneous" case does not apply. It is focused on the cases where either defective equipment or human error during certain activities occurs. That's why 70E-2015 in the "table" based methods has a table for whether or not the activity may pose a hazard and OSHA 1910.269 Annexes have a similar table. Just walking by is not one of those situations. With breakers that are maintained properly, and as I said the arc flash study is garbage if you don't maintain them properly, just operating them is also very unlikely to cause a problem and that's why 70E in the table version of the risk assessment doesn't require arc flash PPE.

As to over-dutied, this means that in the event of a bolted fault condition, it is beyond the breaker's design. Either the breaker (or bus bars) may simply fail to open at all, or it could literally fly apart from magnetic force involved. Without further information it's hard to say what will happen but either way we're talking about bolted faults which are NOT arcing faults. Arcing faults have significantly less fault current involved so breakers might be overdutied in the event of a dead short but might be sufficient to open and clear an arcing fault, if they are still working properly.

Finally, "category dangerous" does NOT EXIST anywhere in 70E. It is a totally fictitious and unscrupulous thing created by one or more software companies. There is a fine print note, NOT PART OF THE CODE, in 70E that mentions a 40 cal/cm2 "cutoff" that applied almost 20 years ago when the highest available PPE at the time was ATPV 40. Now the 100+ ATPV suits are readily available so that note is now just history. I put in the public input to delete it and in the 2018 edition it will be removed.

Second even the fine print note that does exist doesn't have any additional requirements at all in 70E. It just states that "additional caution" should be used which is obviously true even for anything above 1.2 cal/cm2. This is sort of like the "prohibited approach boundary" that was in 70E until a few years ago. 70E had an extra shock protection boundary but no additional requirements so it was removed. Similarly there are no additional requirements for "additional caution" so it is being removed.


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 Post subject: Re: Intent of Arc Flash Labels
PostPosted: Mon May 01, 2017 8:57 am 
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Location: Maple Valley, WA.
NFPA 70E defines an Arc Flash Hazard as:
A dangerous condition associated with the possible release of energy caused by an electric arc.

Informational Note No. 1: An arc flash hazard may exist when energized electrical conductors or circuit parts are
exposed or when they are within equipment in a guarded or enclosed condition, provided a person is interacting with the equipment in such a manner that could cause an electric arc.

Under normal operating conditions, enclosed energized
equipment that has been properly installed and maintained
is not likely to pose an arc flash hazard.

Informational Note No. 2: See Table 130.7(C)(15)(A)(a)
for examples of activities that could pose an arc flash
hazard.

I would highly recommend that you review the table referenced above. This will give you an idea of what activities are considered to by of a high risk for arc flash.

_________________
Robert Fuhr, P.E.; P.Eng.
PowerStudies


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 Post subject: Re: Intent of Arc Flash Labels
PostPosted: Mon May 01, 2017 2:45 pm 
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Hi,
There are several things going on in your post that might need some explanation. BTW, you're sane.

First, you mentioned 12,470 to 480 volt switchboards. Do you mean individual sub stations? I’m thinking these are combination gears. Gears with a transformer connected via bus to a switchboard. Also, are these all switchboards? Maybe some switchgear or some of each?

Second, if you have access to the arc flash report, look at the arc flash spread sheet. There should be columns giving the arcing flash energy as well as boundary and arcing time. I ask because it’s possible the arcing time may not have been stopped at 2 seconds. The idea behind the 2 seconds is someone working on an energized gear should be able to get outside the arc flash boundary in 2 seconds or less. Obviously, if you’re working in a manhole or in a bucket or on a ladder, you may not be able to get outside the arc flash boundary that quickly. So, have a look at the arc time. It’s possible the consultant did not stop it at 2 seconds. That could explain the high boundary distances and Danger. FYI, it used to be that 40 calories was considered the maximum arc flash energy that we could be exposed to before energized work was prohibited. That’s not the case. 70E says there should be increased emphasis on deenergizing if the hazard exceeds 40 calories. Personally, I’d not want to work on something with that much hazard, regardless of how high the PPE was rated. I understand there are 100 calorie suits now. Wow!

On the over duty equipment. I think what they’re referring to is the withstand ratings of the over current devices. Their answer that the report is incorrect is important. If that piece is wrong, what else is wrong? Moreover, if your employer is saying the report is wrong, how did they determine that and what are they doing about it? Any fix where OCD are over duty can be costly to fix but not that costly.

A good video that shows both fuses and breakers reacting when asked to interrupt high current faults can be seen at https://www.youtube.com/watch?v=3dckmSgp1nw. It’s made by Ferraz-Shawmut Fuse. May be take a look at.

Good luck,


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 Post subject: Re: Intent of Arc Flash Labels
PostPosted: Tue May 02, 2017 12:32 pm 
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wilhendrix wrote:
70E says there should be increased emphasis on deenergizing if the hazard exceeds 40 calories. Personally, I’d not want to work on something with that much hazard, regardless of how high the PPE was rated. I understand there are 100 calorie suits now.


This will be gone in the 2018 edition. The thing with this is that it's in a fine print note and not the Code itself. Second, no new or additional requirements are imparted by being above 40 cal/cm2. "Increased emphasis" is not defined. For all practical purposes if this line were kept, it should be changed to 1.2 cal/cm2 because below that point 70E does not require PPE and above that point it does.

There is nothing magical about 40 cal/cm2. If your plant only carries ATPV 10 PPE then for you, you don't have equipment that goes above 10 cal/cm2. If you carry 100 ATPV arc flash suits then for you, you can't use PPE as a solution above that point. In almost any plant that hasn't specifically been designed with arc flash in mind, there will always be some areas of some equipment where there simply is no available PPE. Emphasis on available...not that it doesn't exist but you may not have access to it for whatever reason. This is where frankly we have to get a little creative with how to do things. I didn't say doing unsafe acts...just thinking outside the box like going to the primary side of a transformer to de-energize the secondary side or limiting work to tasks that are not likely to cause an arcing fault.


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