Arc Flash - NFPA 70E
Arc Flash - NFPA 70E
(OP)
For those of you involved at plant sites, have you or are you being encourged to look at the new regulations regarding Arc Flash, and applying Personal Protective Equipment?
Are you (a)complying, (b)ignoring, or (c)stumped on how to respond? I'm trying to figure out just what kind of an impact this is having/will be having on the industry in the US. There seems to be a lot of discussion about this topic.
Thanks
Are you (a)complying, (b)ignoring, or (c)stumped on how to respond? I'm trying to figure out just what kind of an impact this is having/will be having on the industry in the US. There seems to be a lot of discussion about this topic.
Thanks






RE: Arc Flash - NFPA 70E
It is done deal - just a question of when you will get the program implemented. If there is an arc-flash related injury right now in any facility, OSHA can and has levied fines if proper PPE and hazard assessment was not provided.
RE: Arc Flash - NFPA 70E
According to OSHA, they have not directly adopted NFPA 70E (although there ared indirect incorporations of it), but they can make the case.
OSHA apparently will be adopting portions of NFPA70E directly, most likely this winter. That's not to say OSHA can't levy fines, since the safe work practices rule applies & NFPA 70E addresses this. However, OSHA 1910 does not directly reference NFPA70E at this time.
I am interested in people's experience here.
RE: Arc Flash - NFPA 70E
1) offering arc flash training
2) performing arc flash exposure calculations
It seems like a big step when first considered but at the site I am most invovled with, actual deployment has not been a hardship.
This site is an oil refinery with existing PPE requirement of nomex coveralls. Most of the switchgear we analyzed has only an arc flash exposure of '1' (NFPA designation) so we are verifying that the coveralls offer protection of 4 cal/cm sq.
There are a few locations that have exposure of '2' and for those locations an arc flash jacket and face hood is kept handy.
We are presently preparing labels for the entire complex, with modern software (e-tap) the calculations are routine, but making that many labels gets to be a big project.
I feel there are many open liabilities within NFPA 70E, and though it can be used as a consensus/guidline; should not be followed too literally. That may be a reflection on the subjective nature of arc flash phenomena, too many variables to quantify in a code book.
As an example, exposure level 1 requires 4 cal/sq cm protection but no face sheild. Personally I would rather not have my face burned up. One must hope that in an arc flash incident, the worker's face is far enough away to be out of contingency.
RE: Arc Flash - NFPA 70E
There are certainly a lot, maybe a majority, of facilities that haven't done anything yet.
You're right that NFPA-70E is not a mandatory standard in the sense that the NEC is. But OSHA is enforcing the need for arc-flash hazard assessment and PPE already. In the regions were there have been accidents and fines, the pace of adoption has picked up.
RE: Arc Flash - NFPA 70E
Can any of the US engineers involved in this sort of classification give any guidance on how to go about assessing the risks? I'm not really interested in the legislative process because the US authorities obviously don't have any jurisdiction in the UK, but am keen to understand and hopefully apply the assessment methods developed in the US.
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One day my ship will come in.
But with my luck, I'll be at the airport!
RE: Arc Flash - NFPA 70E
We lean very much toward the use of tables to satisfy, in part if not entirely, NFPA 70E. We understand that labeling should be produced for equipment but this will come in due time as the engineers gather all of the pertinent equipment information to use with software programs invoking NFPA 70E and IEEE Std. 1584TM-2000.
Cheers!
RE: Arc Flash - NFPA 70E
You might want to get hold of a copy of NFPA 70E (2004) as a starting place. It's not terribly expensive (compared with IEEE 1584 anyway) This is a "consensus" standard on electrical safety in the workplace (in the US). It's use is not legally required, but our federal OSHA has said that if NFPA 70E is followed, you will meet OSHA requirements for electrical safety.
At this point, most facilities are not in full compliance with all parts of NFPA 70E, but it still serves as good reference for a "model" safety program.
RE: Arc Flash - NFPA 70E
I aggree with dpc. Start with a copy of NFPA 70E and check the hot work portion of it (there is a bunch of other material that you probably have covered with local codes and regulations).
In my case, the arc flash exposure calculations seem MUCH simpler after having reviewed the tables provided by modern software on the calculated values.
The calculations are based on fault current available, voltage, clearing time, distance from the source, etc. It sounds complicated until one sees the printout, which (from ETAP) nicely tabulates the incident radiation exposure in tables with clearing time on the vertical axis, and distance from fault on the horizontal; a unique calculation (and table) for each bus.
NFPA 70E has much empirical information and seeming inconsistencies. When questioning this, I was advised that iw will make work 'safer', a relative term. There in lies a huge liability.
RE: Arc Flash - NFPA 70E
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David Baird
mrbaird@hotmail.com
Sr Controls Designer
EET degree.
Journeyman Electrician.
RE: Arc Flash - NFPA 70E
Notice the notes associated with most aspects of the NFPA 70E PPE selection table. Many times those notes make the table useless.
Be sure you're aware of the TIA issued by NFPA a few months back, modifying the table.
RE: Arc Flash - NFPA 70E
When our site went through the Arc Flash calculations (just prior to the release of IEEE-1584), we used the Duke equations for calculating incident energy and appropriate PPE levels.
Arcing fault current is calculated as a percentage of the bolted fault current; higher percentage as voltage increases. This arcing current is used with existing coordination settings to determine the actual clearing time of a purely arcing fault.
For plant level distribution voltage, this adds significant time to the flash. This is where I really disagree with the IEEE-1584 method. The incident energy (and associated flash protection boundary) increases in direct relation with time even through one minute if that's what the clearing time comes to.
Looking at the test data used by the IEEE team, all (or most) of their tests cleared between 6 and 30 cycles. There were also very few test data points. The empirical formulae were based off a very small sample size and very fast clearing times. In the real world where clearing times are significantly longer (for arcing fault current), the IEEE results yield unrealistically high incident energies and extreme flash protection boundaries.
I believe that the proper way to protect against arcing faults is to implement one of the newer technologies to detect both elevated current and photo sensing such as ABB's ArcGuard system.
As noble an idea as arc flash protection is, my peers are convinced that it was a special interest by one particular chemical company who also makes the fibers which the PPE is made of, since most of the IEEE team was from that same company.
Sorry for running off on a tangent, but is there anything in particular you want to know Scotty? The general workflow for assessing PPE requirements is the following. Once you see a trend, you can assume a worst-case scenario and base your PPE on that.
1. Have an up to date system model or relaying settings on hand
2. Know the 3-phase bolted fault for each level of the system
3. Use some methodology to determine the arcing fault (IEEE, Duke, etc.)
4. Use the arcing fault current along with other assumptions to determine incident energy and flash protection boundary. These assumptions are such things like space between conductors, distance from point where fault occurs, arc in a box or in the open, etc.
5. Label the equipment
After a while, the trends start to develop. 2500KVA (and larger) transformers with 480V secondaries are hard to protect against as there is a lot of available fault current. These are not your friends when performing an arc flash study. Older plant systems that used a lot of fuses don’t lend well to clearing arcing faults quickly. It’s easy to dictate what must be done to get the incident energy down below a point. It’s much more difficult to find the funding required to make such changes.
RE: Arc Flash - NFPA 70E
RE: Arc Flash - NFPA 70E
Steps 3 & 4 are the stages where the UK is kinda living in the dark. Establishing which methodology to use is my first step. There doesn't seem to be much consensus in the US, so you can imagine how difficult it is over here where arc-flash hazard is not really considered.
We have a lot of 2.5MVA distribution transformers operating at 415V secondary. The available fault level at the main load centres is very large, and our equipment doesn't use current-limiting fuses. Most of the MCCBs are old thermal-mag types. We tend to do a lot of fault-finding on the boards with cubicle doors open, and while our PPE is almost certainly better than the majority of UK industrial sites, we don't use the level of personnel protection that our US colleagues would be required to use. I'm probably the first engineer at our site to start trying to quantify the risk based on something other than instinct. We have so many ultra-high energy systems at the power station that we probably don't treat distribution-level circuits with as much caution as we should.
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One day my ship will come in.
But with my luck, I'll be at the airport!
RE: Arc Flash - NFPA 70E
Bottom line is that while doing troubleshooting on or near energized equipment, some protection is required. Our site provides and has standardized on full 65 cal/cm^2 suits including face shields for this purpose. We have some normally closed tie breakers that exceed 65, but we can open them before work to reduce the energy.
The IEEE document is a work in progress in my opinion and should only be used as a guideline. When OSHA incorporates this into electrical safe work practices, I hope there is some flexibility for interpretation.
Our company has had a few arc-flash injuries in the UK and a few saves in the US where arc-flash PPE prevented serious burns. The electricians hate it since it's bulky and hot.
There is no need to perform a full study to protect the technicians, just provide a suit for them to wear during "at-risk" activities. A few examples of "at-risk" activities for us are racking breakers in/out, opening and closing load break disconnects above 480V, performing voltage checks on energized conductors/bus.
RE: Arc Flash - NFPA 70E
This approach can still put technicians in danger where the incident engergy may exceed the rating of a 65cal suit. It is common for situations to arise where no level of protection is adquate and the equipment must be worked de-energized.
RE: Arc Flash - NFPA 70E
Also, the advantage of knowing arc energy levels is that in many locations, a heavy flash suit is not required. A 8 cal/cm2 coverall or shirt and pants with a face shield will suffice in many situations.
RE: Arc Flash - NFPA 70E
RE: Arc Flash - NFPA 70E
I have never had a single person recieve an arc flash injury on any project I have been involved with or led. Neither has my Father, and we have nearly 60 years combined experience in the electrical industry. At the same time, we have both been involved on projects where fatalities occurred from falls.
Bigbillnky,C.E.F.....(Chief Electrical Flunky)
RE: Arc Flash - NFPA 70E
the Canadian Standards Association (CSA) does not currently have a standard equivalent to NFPA 70E. Nonetheless, when hearing a case, the court decides on the standard of care by asking what a reasonable person with same background or expertise would have done in the same circumstances. In the absence of such a document, many companies in Canada adhere to the NFPA 70E standard. Check
http://w
RE: Arc Flash - NFPA 70E
All in all, if you've seen an arc flash and the resultant injuries, you will gain a great respect for the hazard analysis and the PPE that comes out of that.
RE: Arc Flash - NFPA 70E
bigblinky: You have had good luck. Unfortunately things don't work out so well for everyone. I'm an engineering consultant, not a contractor, but have been associated with serious accidents on two projects. In the first an electrician (not wearing PPE) was seriuosly burned over 50% of his body by arc flash when he apparently dropped a tool on live 480 V bus. In the second the worker shorted a 480 V bus upstream of the main disconnect with a metal fish tape. Fortunately the switchboard was not open at the time and there were no seriuos injuries but I still have the melted section of bus bar.
RE: Arc Flash - NFPA 70E
I have conducted a number of Arc Flash studies in the UK in the past year,using SKM Power Tools software,for a USA based client.The calculation of the 3 phase fault levels were made using the IEC 60909 and the G74-Engineering recommendations.We used the IEEE 1584 although the same software will calculate to the NFPA 70E as the standard to calculate the let through energy (j/cm2) and converted this to cal/cm2.This seem to be the standard unit used by one USA/UK based PPE clothing manufacturer.
The principal I think is excellent,however there are a lot of lessons to be learnt,also there is little experience of the application of safety labels and the actual when/where to apply the PPE.I speak only from experience in the Paper & Pulp industry.
The very small number of personnel over the years who I have met who received dreadful burns after electrical accidents I think would have been in favour of PPE
(my first message,please excuse my spelling!)
RE: Arc Flash - NFPA 70E
Would like to discuss this further. We have pretty good fault level data at most of our primary load centres, but currently use ERA's ERACS software for load flow and fault studies. I'll enquire with them whether they have a module capable of doing arc flash analysis or whether we're looking at spending lots of money on another analysis package or lots of money on a consultant. I'm gonna be popular either way!
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One day my ship will come in.
But with my luck, I'll be at the airport!
RE: Arc Flash - NFPA 70E
The arc flash calcs are a function of the fault energy and the clearing time. The above discussion surrounds the arc energy. The problem usually seems most aggravating with main breakers, which are often applied without instantaneous elements, or settings which are so high so as to be almost non-operable.The problem is quickly solved if the fault clearing time of the protective device can be decreased.
A couple of suggested approaches:
1) A temporary maintenance switch switch which would either speed up or otherwise enable a sensitive instantaneous element (on a main breaker, for example) which thereby GREATLY reduces the energy to a manageable level. The temporary miscoordination would usually be acceptable. (Instead of a switch, use a timer to avoid forgetting toi turn it back to normal!)
2) Another idea - I have seen the suggestion made to install a motion detector & use this in lieu of the above switch - anyone in the affected area enables a fast tripping method which decreases the incident energy. I've personally never applied this, but it seems like a very slick idea.
3) Applying a zoone selective system for faults insoide the zone would also be effective (but more costly) than the above. By the way - does anyone know what is the ANSI symbol or approved terminology for this protection scheme? I've seen it discussed for years, but I'm not sure how to call it out, as it is not technically a differential (ANSI device 87).
Your thoughts?
RE: Arc Flash - NFPA 70E
RE: Arc Flash - NFPA 70E
ABB's answer routes a leaky optical fiber through the switchgear. Any bright light is assumed to be an arc and instantaneous tripping is initiated. For demo, they used a camera flash. No photos please.
RE: Arc Flash - NFPA 70E
The multiple setting idea is a good one, although outside of a medium voltage relay, you will find only one low voltage circuit breaker manufacturer that has a multiple setting option. You can activate the lower (more sensitive) settings with any contact input, such as a motion detector, key switch at the door, or push button with timer. I don't suggest the motion detector, since when the janitor is in the room, I don't want to lose selectivity. The timer is not recommended because I don't want to be the guy working on the equipment, and it may take longer than expected, and the settings go back and I don't realize. I like the key switch at the door with a rotating yellow beacon outside to indicate the "maintenance" settings are activated.
Even better is zone selective interlocking, since many newer breakers already have the capability but it is not used. It offers automatic setting changes depending on whether there is a fault downstream or in the SWGR itself. If the fault is downstream, essentially the instantaneous on the main CB is deactivated, allowing the feeder CB to clear the fault. If it doesn't, then the main will trip after delay. If the fault is in the SWGR, then the main CB has its instantaneous protection enabled and trips quickly. This gives many benefits with little risk, just specification of the trip unit, some control wiring between breakers in the SWGR.
I'm hoping you will see an article about these choices shortly in the IEEE Industry Applications Transactions, soon. :)
RE: Arc Flash - NFPA 70E
One implementation concern is how to verify that the relays all received the signal and did, in fact, switch to the more restrictive setting. Because this is safety-related, it might advisable to get some type of feedback from each relay, in the form of a contact output, to verify that it is in the maintenance mode.
Has anyone tried to tie a 480V zone selective interlock circuit to an upstream medium voltage relay?
RE: Arc Flash - NFPA 70E
RE: Arc Flash - NFPA 70E
Thanks for the info - I thought there might be some interface issues. There is quite a bit of potential for reduction of arc-flash at main 480V breakers if this could be done, so I would expect someone to come up with a solution.
I don't think all of the 480V ZSIs are implemented the same way either, so it might have to be specific to each trip unit vendor.
RE: Arc Flash - NFPA 70E
Sorry not replied sooner,have you been able to establish whether ERA's ERACS software has an Arc Flash Evaluation software module?.
Your comments suggest you have accurate site data re:protection device"As Found" settings,transformer details etc.I appreciate to remodel on SKM Power Tools or Easypower would be costly,although once items are modelled and coordination graphs established running an Arc Flash Study is fairly straight forward,once you understand the permutations.
I have found that creating Scenarios for "proposed settings" re: reducing instantaneous values/time,fuse sizes etc to reduce the classifcation,then rerunning the Arc Flash study can be very time consuming.Another factor is how many protective devices have to be modelled from scratch using manufacturers literature.For example I have found SKM Power Tools libary containing European LV MCCB's limited.
Let me know if you require any further info
RE: Arc Flash - NFPA 70E
I am a UK Engineer working in the Oil & Gas sector. We are in the process of purchasing SKM PowerTools to carry out our study. We will be using the arc-flash module as previously described.
We have made contact with PPE suppliers in this area and are moving forward with the project, albeit slow at the moment.
I can share information as and when I have it if you want.
regards
RE: Arc Flash - NFPA 70E
ERACS doesn't appear to have the facility for this yet, so I'm going to have to look at using something like SKM. I'll have to get some backing from our H&S manager on this to help push it along, but I think I will be supported in it. I'd be delighted to share info as we progress.
What industry are you from? I'm in powergen at a CCGT site on Teesside.
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One day my ship will come in.
But with my luck, I'll be at the airport!
RE: Arc Flash - NFPA 70E
I have been predominatly working in the UK/Europe Paper & Pulp Industry over the last 10-15years,but only came into contact with Arc Flash Studies early last year.
The studies I have conducted are based on using SKM Power Tools software - CAPTOR & DAPPER incorporating IEC60909
Fault Analysis
I too would also be delighted to share "lessons learnt".
Here are a few to start off with for comment,based 1st on the short circuit study:
1)Obtain all the scenarios from the Supply Utility re;Ibreak,Ipeak and X/R ratios for the incoming point of supply.Other consumers connected to the same supply(MV) may have embedded generation which can add to the fault level.
Only became apparent when I requested the supply X/R ratio!
2)Obtain a copy of the G74 Engineering Recommendation.The UK Utilities I was obtaining Fault Level info from,refer to this document.It is also very useful e.g.in identifying values of X/R ratios for large synch/asynch machines,if you don't have access to data re; older machines
3)Obtain a copy of the IEC60909-A must.The references and diagrams explaining fault contribution for the near-and-far fault contribution from large generators/motors I found particularly useful.This also helped to understand which parameters to set in SKM when dealing with motor fault contributions re; first 5/6cycles or otherwise
4)I didn't use the SKM power tools default values for transformer X/R ratios based on %Z,calculate from transformer losses etc.The SKM default values can produce inaccurate Ipeak values.
5)Obtain typical UK(50Hz)motor supplier r/x and locked rotor/FLC values-more accurate then SKM default values.
Similarly I checked cable data with a major European cable manufacturer-The SKM cable databse were fine(SWA/XLPE/PVC)
6)The G74 document is very useful as a guideline for x/r value and ratio of locked rotor/rated current if you have large regen/active rectifier static invertors/convertors (600-1500kW in my case),but don't have equipment actual values.I contacted SKM on this topic but felt that their reply was not what I had expected,so used the G74.
Incidentally the short circuit analysis was specifically also used to identify that bus,switchgear ,ACB/MCC's etc were adequately fault rated re:Ibreak and Imake(Ipeak)
The coordination study was also used to identify that discrimination was being met and to see whether improvements could be made.
If this is of any help I will list my other"lessons learnt" on the coordination and Arc Flash studies in due course.Would be interested to share your experience
RE: Arc Flash - NFPA 70E
We have our own internal supply network, so that should be easy in that we won't have to go begging to the DNO for information. The site is relatively young so a lot of data should be available for the equipment.
We have a lot of rotating plant including a 53MVA embedded 11kV generator and some pretty big motors. It sounds like I'm going to be looking at migrating from ERACS to PowerTools to progress this - I'm going to be stuck for a while until I can get the funding sanctioned (probably next budget year).
Thanks for taking the time to post so much information - much appreciated. LPS for you!
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One day my ship will come in.
But with my luck, I'll be at the airport!