It is currently Thu Feb 22, 2018 3:44 am



Post new topic Reply to topic Go to page Previous  1, 2
Author Message
ekstra   ara
 Post subject: Re: PUC Cases
PostPosted: Fri Dec 08, 2017 4:52 am 
Offline
Plasma Level
User avatar

Joined: Wed May 07, 2008 5:00 pm
Posts: 711
Location: Rutland, VT
Thanks Jim. That is my intention and if goes as far a Formal Request, I think that is a public record that I can post and it can be used when running into difficulties obtaining the information.

_________________
Barry Donovan, P.E.
www.workplacesafetysolutions.com


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: PUC Cases UPDATE
PostPosted: Tue Dec 19, 2017 8:45 am 
Offline
Plasma Level
User avatar

Joined: Wed May 07, 2008 5:00 pm
Posts: 711
Location: Rutland, VT
The utility has relented to release the information to me after discussions with the State PUC. Apparently this will be only for me and they have to go out to the field to gather the information related to transformers, fusing, riser cable, etc which sounds like they do not have good records for equipment attached to their lines.

They also told the PUC that they will be developing a formal policy to handle these requests. The Deputy Director of the PUC cautioned the utility to be sure that requirements such as OSHA, NFPA70E and the NEC are taken into account in the new policy.

What helped was providing the PUC with lots of documentation showing why this information is needed. I think the example that drove home the importance of utility available fault current was providing an example of a model using actual utility fault current values and a model using the infinite bus values provided by the utility. It was an eye opener, especially for the PUC, to show the infinite bus results on several pieces of equipment was 1 cal/cm2 but with the actual values the incident energy was 12-14 cal/cm2.

I have asked the PUC representative to obtain a copy of the new policy when it is written so I can review it. I suspect that when they start developing the policy, which I think will try to be slanted to not providing the information, they will run into issues with codes/standards/regulations.

I am also surprised that other people during this type of work in this utilities territory have not experienced this or maybe it was too much effort and they used an alternate method.

_________________
Barry Donovan, P.E.
www.workplacesafetysolutions.com


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: PUC Cases
PostPosted: Tue Dec 19, 2017 12:25 pm 
Offline

Joined: Wed Jul 12, 2017 6:06 am
Posts: 9
Glad to see we aren't the only ones fighting these battles. I find a lot of inconsistencies with the utilities I have dealt with. We did two different studies in Mississippi this year and Entergy was the utility. These plants were only about 20 miles apart but were in different districts for Entergy, so I dealt with different engineers. I got calculated primary fault current data for one plant and the other district would only send me secondary infinite bus calcs. I am going thru this now on a job in South Dakota with Xcel Energy.

We have another job in Arkansas that has a small co-op and they are charging because they don't have an engineer on staff and have to pay a consultant to do the calcs. I am ok with that because most of our customers are willing to pay for the correct data, but it burns me up when you explain to the utility why you are asking for what you are and they send a form with infinite bus numbers on it. :oops:

On a similar note when you get infinite bus are you just running with those numbers or are you doing the calcs at say 50% or 75% infinite bus and doing a worst case scenario?


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: PUC Cases
PostPosted: Tue Dec 19, 2017 2:38 pm 
Offline
Plasma Level
User avatar

Joined: Wed May 07, 2008 5:00 pm
Posts: 711
Location: Rutland, VT
So far I have been successful with getting actual utility data but I did see an IEEE paper that discussed that 50% of infinite bus appears to be the conservative option.

_________________
Barry Donovan, P.E.
www.workplacesafetysolutions.com


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: PUC Cases
PostPosted: Wed Dec 20, 2017 2:53 pm 
Offline
Plasma Level
User avatar

Joined: Mon Sep 17, 2007 5:00 pm
Posts: 1245
Location: Scottsdale, Arizona
Congratulations! and as mentioned before, thanks for keeping us all informed of the progress and how it turned out. A good case study for others!


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: PUC Cases
PostPosted: Thu Dec 21, 2017 1:28 pm 
Offline
Arc Level

Joined: Tue Jan 13, 2009 5:00 pm
Posts: 442
wbd wrote:
So far I have been successful with getting actual utility data but I did see an IEEE paper that discussed that 50% of infinite bus appears to be the conservative option.


Reference please.


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: PUC Cases
PostPosted: Fri Dec 22, 2017 6:03 am 
Offline
Plasma Level
User avatar

Joined: Wed May 07, 2008 5:00 pm
Posts: 711
Location: Rutland, VT
The paper is titled "Impact of Available Fault Current Variations on Arc-Flash Calculations" By I. Balasubramanian and A. Graham. It was published in IEEE Transactions on Industry Applications (Vol 46, Issue 5) and is available from IEEE.

_________________
Barry Donovan, P.E.
www.workplacesafetysolutions.com


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: PUC Cases
PostPosted: Fri Dec 22, 2017 9:32 am 
Offline
Arc Level

Joined: Tue Jan 13, 2009 5:00 pm
Posts: 442
wbd wrote:
The paper is titled "Impact of Available Fault Current Variations on Arc-Flash Calculations" By I. Balasubramanian and A. Graham. It was published in IEEE Transactions on Industry Applications (Vol 46, Issue 5) and is available from IEEE.


Found it. This is awesome, they iterated in 10% increments from 10% to 100% of the infinite bus bolted fault current. 50% yielded to most incident energy in all four of their sample systems. Knowing this, do you really care that much about the source impedance ahead of the service transformer as the system is configured today? It is guaranteed the system will be reconfigured either temporarily for maintenance, or permanently for load growth or ease of maintenance. Using 50% avoids these eventualities, leaving only the possibility of a transformer replacement changing calculated IE results.

Thanks and Merry Christmas.


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: PUC Cases
PostPosted: Fri Dec 22, 2017 11:00 am 
Offline
Plasma Level
User avatar

Joined: Wed May 07, 2008 5:00 pm
Posts: 711
Location: Rutland, VT
The benefit to modeling from the utility protective device (usually fuses), riser cable (if padmount), utility transformer, and secondary conductors to the service equipment (switchgear, MCC, Switchboard) is that the utility protective device sometimes will keep the incident energy down on that service equipment. Not to mention having the utility available fault current.

Using just the 50% of infinite bus fault current only leaves the option of using 2 seconds for the arcing time which usually leads to a high incident energy level which can cause issues in the facility. For example: if the service equipment is an MCC, the entire MCC will have that high IE which could be above 40 cal/cm2. So if there is no PPE, how do you open the door on a bucket to change overloads or a fuse on the control transformer.

The other point is that with X/R ratio from the utility, the duty rating of devices can be verified.

_________________
Barry Donovan, P.E.
www.workplacesafetysolutions.com


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: PUC Cases
PostPosted: Fri Dec 22, 2017 12:42 pm 
Offline
Plasma Level
User avatar

Joined: Tue Oct 26, 2010 9:08 am
Posts: 1878
Location: North Carolina
wbd wrote:
Using just the 50% of infinite bus fault current only leaves the option of using 2 seconds for the arcing time which usually leads to a high incident energy level which can cause issues in the facility. For example: if the service equipment is an MCC, the entire MCC will have that high IE which could be above 40 cal/cm2. So if there is no PPE, how do you open the door on a bucket to change overloads or a fuse on the control transformer.


First off, 40 cal/cm2 is not really a valid "limit" of any kind. It's an arbitrary one and more or less a historical one at that. Currently many utilities are stocking and using 100 cal/cm2 PPE and higher levels are available. However regardless of what your "cutoff" is at some point we have to agree that there is a practical limit to "throwing PPE at it", regardless of whether it's 12, 40, 100, or even higher.

This gets to the crux of the issue. Can you document evidence of arc flash caused by opening a door? And is this even the root cause or something else? When going through 5 years of OSHA electrical injury data I found only a single case where opening the door induced an arc flash. The details were that basically in a previous repair the electrician sort of jammed a piece of sheet metal in the door to "fix" the panelboard and subsequently when someone opened it, the sheet metal fell out and induced the arc flash. So the root cause was extremely crappy maintenance, not the initiating event that was opening the door. If the poor workmanship had been addressed then this incident would never happen.

This brings us back to the crux of the issue. I'm pretty sure that there is never any such thing as a true guarantee that accidents won't happen. In over 2 decades of various accident investigations, root cause analyses, hazard analysis projects, etc., the level of creativity of idiots as well as the level of creativity of the most ridiculous and insane "what if" scenarios is truly astounding. If someone invokes hostile enemy missile strikes, tornadoes, tsunamis, tornadoes, or ball lightning anymore in these investigations, I don't even blink. I would argue that first off we have to recognize that hazards exist not only in the work place but everywhere. Not addresising them at all is just as bad as addressing hazards where the likelihood is so ridiculously remote that doing so is a waste of time. For instance should we erect anti-meteor shields over the parking lots at the office just in case a meteor strike occurs? Probably not because although the evidence is pretty clear that being struck by a meteor is a fatal event, the likelihood is extremely remote. What we would want to do is to take steps to actively prevent, limit the injury, or in the worst case use PPE to reduce either the likelihood or severity of injury due to electrical hazards to about the same as other similar injury sources in the work place. Doing any less would fail to address the issue sufficiently and doing any more than that is completely unnecessary. Since the likelihood of a vehicle fatality on the way to work is already something like 3 to 5 times more likely than an arc flash injury or fatality ON AVERAGE, then obviously most of the time we shouldn't be doing anything at all. Simply statistics seems to suggest that overall electrical equipment is inherently quite safe to operate and maintain as proven by decades of actual recorded historical data. Thus the overemphasis on arc flash (to the point of ignoring shock hazards which are both far more likely and fatal) is inherently poor decision making, driven by political forces and the inherent "newness" of the hazard, and the fact that the videos of things blowing up always gets people excited and interested.

The crux of the issue and this is where for the most part 70E is remiss is that PPE is NOT the solution to every situation. In fact 70E-2015 is quite clear on this and 70E-2018 makes it even more clear. We need to recognize that many tasks are not inherently hazardous in the first place, and that no matter what task is, some equipment is not inherently hazardous in the first place either by virtue of design and condition (e.g. 600 V class MCC's properly installed and maintained) or due to the lack of energy (e.g. a residential receptacle). It's only when we combine the two...doing an inherently hazardous task on inherently hazardous equipment that we need to take steps.

As to your example of opening doors, as I said, this is pretty darned unlikely almost no matter what the equipment is. A simple visual inspection looking for obvious problems such as soot/char around the door, liquids seeping out of the door, or severe rust or contamination are obvious hints. Since the latest edition of NEC now requires marking anything that has exposed electrical conductors behind the door it should be inspected and marked ahead of time to indicate where and when there is an inherent danger so that opening the door is NOT exposing anything energized. Note that this uses the definition of "exposed" (not insulated, guarded, or inaccessible). Energized conductors might be visible but the "inadvertent contact" test applies. So if there is no "exposed parts inside" label (to paraphrase 70E language) label, then PPE isn't automatically needed for opening the door. This requires up front work...about the same amount as required to do a survey for an arc flash engineering study.

Once you pass that test and get the door open as to the rest of the issues (changing an overload or fuses) with the disconnect/circuit breaker open, unless there is a problem where the incoming connections are located, at least within MCC's I haven't seen any real issues in practice. It might require installing some kind of temporary guarding with rubber blankets or glastic pieces to eliminate the problem of exposed conductors but once that's out of the way, these tasks are not likely to cause an arcing fault within an MCC bucket.

Within an industrial control panel since the tendency is to put everything everywhere without regard for safety or personnel working on them, powering down might be the only practical option but that's not typically what I would see for distribution equipment in the first place so it's not likely to be connected directly to a utility feed. On many of these types of panels it is easily possible to add some additional barriers to convert it into guarded equipment.

Don't forget that this is protection against INADVERTENT contact. What does this mean in practice? What about industrial control panels? If we go back to the original sources for the shock hazard section of 70E, IEEE 516, it gives everything in terms of the "MAD" or Minimum Approach Distance. MAD is a combination of both the distance required to avoid potentially arcing over (previously called "prohibited approach boundary in 70E editions) AND an inadvertent movement adder. In other words for instance with 480 V where the restricted approach boundary is 12", also known as the MAD or minimum approach boundary, work going on 12" away horizontally is safe. In the vertical direction we need to consider dropped tools. Inadvertent contact isn't going to occur closer than this. In terms of "guarded" IEC has some definitions regarding "finger safe" that are highly applicable to proving that equipment is sufficiently guarded against ANY contact (meeting the accessibility rule).

So to answer your question the simple answer is that you need to perform ALL THREE studies required by 70E. The first one is a shock hazard survey. The second is the arc flash survey. And the third is the risk survey (likelihood of occurrence). Doing only one or two is incomplete and the reason that most people are finding so much difficulty with applying 70E in practical situations.

Doing the arc flash and shock studies lets you screen off a few "low energy" cases where PPE is not necessary no matter what the task but doing the risk analysis shows when PPE is even necessary in the first place. The 2015 edition (warts and all) makes an attempt at doing this for the table-based approach but those doing engineering studies need to also perform a risk asessment which is NOT the same as a hazard assessment. As an example for the holidays, turkey, red meat, and many fruits and vegetables contain substances which are either confirmed or suspected to contain carcinogens as published on the various lists maintained by the IARC. IARC however ONLY looks at hazards, NOT risks. Does this mean that Thanksgiving and Christmas dinners, and for that matter outright healthy eating should be outright banned forever? No of course not because the problem is that IARC does not consider the risks...how much of a particular food needs to be ingested, the chance of getting cancer, or problems with it building up in your system. Doing an arc flash study and ignoring the risk assessment or doing a poor one (everything is going to kill you! The sky is falling! The sky is falling!) is utterly stupid and gets into all kinds of ridiculous scenarios such as wearing a 40 cal suit to turn on a light switch, or opening a door, or changing a fuse on a control power transformer, or probably even using the restroom.


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: PUC Cases
PostPosted: Fri Dec 22, 2017 1:56 pm 
Offline
Plasma Level
User avatar

Joined: Wed May 07, 2008 5:00 pm
Posts: 711
Location: Rutland, VT
Please see where NFPA 70E-2018 Table 130.5(C) has the Eqpt Condition listed as Any and the Likelihood of Occurence as Yes for opening hinged doors to expose bare energized electrical conductors and circuit parts. Therefore you should have PPE on especially if you are testing for de-energized state. Makes no sense to open the door without out the AR PPE and then have to put it on to test. As you pointed out there is shoddy workmanship, so why take the chance.

As far as Risk Assessment, that is not my job. I perform the arc flash studies, make recommendations and submit it to the client. The clients electrical safety program and job task analysis is where the risk assessment part comes in.

_________________
Barry Donovan, P.E.
www.workplacesafetysolutions.com


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: PUC Cases
PostPosted: Fri Dec 22, 2017 2:17 pm 
Offline
Arc Level

Joined: Tue Jan 13, 2009 5:00 pm
Posts: 442
wbd wrote:
The benefit to modeling from the utility protective device (usually fuses), riser cable (if padmount), utility transformer, and secondary conductors to the service equipment (switchgear, MCC, Switchboard) is that the utility protective device sometimes will keep the incident energy down on that service equipment. Not to mention having the utility available fault current.

Using just the 50% of infinite bus fault current only leaves the option of using 2 seconds for the arcing time which usually leads to a high incident energy level which can cause issues in the facility. For example: if the service equipment is an MCC, the entire MCC will have that high IE which could be above 40 cal/cm2. So if there is no PPE, how do you open the door on a bucket to change overloads or a fuse on the control transformer.

The other point is that with X/R ratio from the utility, the duty rating of devices can be verified.


Suggestions: Model 50% Infinite bus with the actual primary protective devices, unless longer than 2 s.
Duty rating of devices should be performed at 100% infinite bus to ensure devices last the life of the installation.


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: PUC Cases
PostPosted: Sat Dec 23, 2017 7:19 am 
Offline
Plasma Level
User avatar

Joined: Wed May 07, 2008 5:00 pm
Posts: 711
Location: Rutland, VT
The actual primary protective device is owned by the utility and they may or may not provide that information.

_________________
Barry Donovan, P.E.
www.workplacesafetysolutions.com


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: PUC Cases
PostPosted: Tue Dec 26, 2017 9:49 am 
Offline
Arc Level

Joined: Tue Jan 13, 2009 5:00 pm
Posts: 442
wbd wrote:
The actual primary protective device is owned by the utility and they may or may not provide that information.


Malpractice to not provide the info in my opinion. While I can understand reluctance to provide source impedance that may change from day to day, the primary fuse on a service transformer is pretty static and likely to change only if the transformer is replaced with a different size. I'd be asking to speak with a PE at the utility, and explain this is a safety issue. Next stop would be the licensure board.

You can find fusing tables at Cooper and S&C based on kVA. Not perfect, but perhaps find a conservative clearing time could be found that is still less than 2s. I suppose the utility might withhold the transformer kVA, but many label them clearly.


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: PUC Cases
PostPosted: Thu Dec 28, 2017 9:20 am 
Offline
Plasma Level
User avatar

Joined: Tue Oct 26, 2010 9:08 am
Posts: 1878
Location: North Carolina
stevenal wrote:
wbd wrote:
The actual primary protective device is owned by the utility and they may or may not provide that information.


Malpractice to not provide the info in my opinion. While I can understand reluctance to provide source impedance that may change from day to day, the primary fuse on a service transformer is pretty static and likely to change only if the transformer is replaced with a different size. I'd be asking to speak with a PE at the utility, and explain this is a safety issue. Next stop would be the licensure board.


Might be different but in NC and several other states utility engineers are not required to be licensed. Even then this typically falls into the industrial exemption so there is no license to go after or any practicing without a license basis, so the license board has no standing.


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: PUC Cases
PostPosted: Fri Dec 29, 2017 1:50 pm 
Offline
Arc Level

Joined: Tue Jan 13, 2009 5:00 pm
Posts: 442
Not legally required doesn't mean licensure is not required or desired. In my experience utilities look for at least an EIT.

https://www.indeed.com/q-Utility-Engineer-jobs.html

So no PE, verified? Ask to speak with the safety officer. He/she better be familiar with the concept of at flash.


Top
 Profile Send private message  
Reply with quote  
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 36 posts ]  Go to page Previous  1, 2

All times are UTC - 7 hours


Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Jump to:  
© 2017 Arcflash Forum / Brainfiller, Inc. | P.O. Box 12024 | Scottsdale, AZ 85267 USA | 800-874-8883