Arc-Flash

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rbarnett's picture
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Joined: 2014-03-04

Arc-flash is hot topic and big buzz-word in the industry these days. I think we see more and more analysis being done and labels posted on equipment. But, how many out there have Arc-flash Warning Labels on your equipment, how many are using the 70E tables and how many are not yet addressing the arc-flash issue? It would be interesting to hear what everyone else is doing.

sparkyjim's picture
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Joined: 2012-08-19

I work in an industrial plant that has labels with PPE requirements on all of our equipment. Following the PPE recommendation seems to be optional. I believe this is due to a lack of understanding/appreciation for what could happen.

Zapper's picture
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Joined: 2013-10-28

I work for a large corporation with over 500 facilities. We are in the process of collecting data on our facilities, creating system models using SKM software, checking the coordination, performing A/F calcs, and posting labels. Once labels are posted in a facility, we purchase any necessary PPE and provide training for all of the facility personnel. This has been estimated to take several years and we are at the end of the first year.

Bob Driggers's picture
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Joined: 2013-11-13

OSHA will not think PPE is optional should there be injuries associated with not using the appropriate PPE.

Buzz Lightbeer's picture
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Joined: 2014-03-10

The manufacturing plant I work at has labeled everything, sent us to training twice and furnished us with individual PPE.

jasonschaefer's picture
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Joined: 2013-11-14

The best thing we can do is mitigate fault current potential. We have found that installing a fusible disconnect with low peak fuses between a transformer and a panel can easily drop a category 3 or 4 panel to a category 0. Arc flash Suits are hot and cumbersome and can present their own hazards. Whenever possible, fault currents should be mitigated.

Mike b's picture
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Joined: 2013-10-28

Unfortunately I work for a family business and even though they push safety they are not willing to send anyone. I have taken the task upon myself to protect the guys that work for me by getting the correct PPE. It is a shame that money comes before safety, but I have found this in most places I work. Until someone gets hurt then that changes the whole thing.

mdshunk's picture
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Joined: 2014-03-14

What troubles me most about the arc flash warning labels is the clear FACT that if you get three different guys (or, three companies) to do the calcs and make the stickers up, you'll get three different results on all but the most straightforward panels. Even if (big IF) the decal is completely proper, among the population of electricians and maintenance techs who (might) read them, how many among them TRULY know how to interpret the information? In my experience, darned few. Even among those that can properly interpret the information on the label, how many heed what it says? How many are encouraged not to? How many just don't care?

rbarnett's picture
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Joined: 2014-03-04

I would "assume" if the correct data is entered the resulting calculations should all be the same. My two big concerns are: 1) clearing times on breakers -- how reliable is that number and 2) if using the tables how many really gather the required information to use the tables -- clearing times and fault currents.

It is good to see progress being made with labels.

sparky377's picture
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Joined: 2013-10-07

RBarnett:
It's my understanding the manufacturers perform testing to determine the trip curves for their overcurrent protective devices. So I have no problem using those "numbers" to coordinate the system and perform an arc flash analysis. Besides there are too many simplifying assumptions made in order to make system analysis achievable.

sparky377's picture
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Joined: 2013-10-07

mdshunk:
If you have competent engineers following IEEE 1584 procedures and using quality software, then the resulting calculations and labels should all be reasonably similar enough for all practicable purposes that they are the same. If you have different results from different consultants, then you have a problem with the consultants. That is another matter altogether.
Regarding the electricians and maintenance personal; they had better be reading them and have the training to understand what the information on the label means. If they are not reading the labels and do not know what the information means, then they are not qualified to be doing the work in the first place. And if they are not wearing the proper protective equipment in accordance with the label, then I suspect they are in violation of company policy and OSHA requirements and could lose their job.
OSHA requires these studies and labels to help workers do their job safely and go home at the end of their shift. Any worker that does not comply, encourages others to ignore safe work practices, or just does not care is a danger to himself and those around him.

sparky377's picture
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Joined: 2013-10-07

jasonschaefer:
I am curious. How did you determine using current limiting fuses would reduce your PPE Category Level from 3 or 4 down to 0?
Using fuses can actually result in an increase of incident energy and increase the level of PPE required. Average arcing type fault on a 480VAC system will typically be 50% of the bolted fault. For 208VAC systems that number drops to 20% to 30% of the bolted fault. This means the fault current may not be high enough to be in the current-limiting range of the breaker or fuse. This means it could take much longer than you are expecting for the fuse to open and interrupt the fault. As the energy is proportional to the square of the time (It^2) a doubling of the time to clear the fault results in 4 times the explosive energy.
A PPE Level of 0 (which I understand is being eliminated in the next 70E revision) based on using fuses may be correct for your facility and present arrangement of distribution equipment. However, if they are not based on an arc-flash hazard analysis performed by a licensed Professional Engineer, then it would be my opinion to be concerned. Only a complete study by performed by a P.E. will truly tell you the level of PPE required at each equipment and device.

rbarnett's picture
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Joined: 2014-03-04

All good points Sparky. I think we often "assume" current limitation reduces incident energy. Obviously, this is not always true.
My comment on the clearing times is not a question of the manufacturer's time-current curve; but of a lack of maintenance. The T-C curve on breakers is reliable over time only if maintenance is performed. Unfortunately, I don't think we do a good job of maintenance over time. In fact, many labels have a caveat at the bottom of the label in small print.
I also understand the 2015 70E will require to identify installation and maintenance issues when using the tables. Interesting times ahead!

Electrical Safety's picture
Joined: 2014-10-21

An Arc Flash is an electrical explosion due to a fault condition or short circuit when either a phase to ground or phase to phase conductor is connected and current flows through the air. Arc flashes cause electrical equipment to explode, resulting in an arc-plasma fireball.

bryti's picture
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Joined: 2013-10-04

[quote=sparky377]jasonschaefer:
I am curious. How did you determine using current limiting fuses would reduce your PPE Category Level from 3 or 4 down to 0?
Using fuses can actually result in an increase of incident energy and increase the level of PPE required. Average arcing type fault on a 480VAC system will typically be 50% of the bolted fault. For 208VAC systems that number drops to 20% to 30% of the bolted fault. This means the fault current may not be high enough to be in the current-limiting range of the breaker or fuse. This means it could take much longer than you are expecting for the fuse to open and interrupt the fault. As the energy is proportional to the square of the time (It^2) a doubling of the time to clear the fault results in 4 times the explosive energy.
A PPE Level of 0 (which I understand is being eliminated in the next 70E revision) based on using fuses may be correct for your facility and present arrangement of distribution equipment. However, if they are not based on an arc-flash hazard analysis performed by a licensed Professional Engineer, then it would be my opinion to be concerned. Only a complete study by performed by a P.E. will truly tell you the level of PPE required at each equipment and device.[/quote]

I believe Jason is referring to a mitigation method that covers the transformer secondary "blind spot". Since you can remove the risk from the line side of the Panel/MCC/SWBD and transfer it to a disconnect that is external and less likely to be worked on or in. This will work with either fuses or in some cases a static/electronic trip breaker.

The intent of mitigating incident energy is to get it out the electricians space, however, realizing the most effective way to mitigate is to get to a zero energy state.

One man's opinion.

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