It is currently Fri Feb 23, 2018 11:28 am



Post new topic Reply to topic
Author Message
ekstra   ara
 Post subject: Two Category System
PostPosted: Mon Mar 09, 2015 9:45 am 
Offline

Joined: Fri Feb 13, 2015 9:27 am
Posts: 8
Location: Hendersonville, TN
We have a proposal from a vendor that will deliver a two category system (4&2) that is much less expensive than a full arc flash analysis. How is the assessment for a two category system completed vs a full assessment?


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: Two Category System
PostPosted: Tue Mar 10, 2015 5:50 am 
Offline
Arc Level

Joined: Mon Jan 18, 2010 11:35 am
Posts: 445
Location: Wisconsin
EWB Engineering wrote:
We have a proposal from a vendor that will deliver a two category system (4&2) that is much less expensive than a full arc flash analysis. How is the assessment for a two category system completed vs a full assessment?

Remember, you don't get what you don't pay for.

there is more to NFPA70E, and OSHA compliance, than simply applying some labels.


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: Two Category System
PostPosted: Tue Mar 10, 2015 6:18 am 
Offline
Plasma Level
User avatar

Joined: Tue Oct 26, 2010 9:08 am
Posts: 1880
Location: North Carolina
With regards to the shock hazard part of an electrical hazard risk assessment, there are essentially only three elements to worry about. The first one is establishing rules and procedures to addressing shock hazards. These are well defined in IEEE Standard 516. 70E and OSHA reference IEEE Standard 516. Both "simplify" it but end up missing some key points of understanding so it creates confusion as to how to properly implement. My advice is to go back to IEEE 516 for understanding first.

The second element has to do with NFPA 70 (NEC). With prior editions any time there was exposed equipment or exposed equipment over 600 V behind a door/panel, it had to be labelled. As of the 2014 edition this label requirement has been extended to any voltage over 50 V. Thus with the exception of making modifications to equipment, there should be labels present anywhere that exposed or potentially exposed equipment exists.

The third element is mitigation. The field survey that identified exposed equipment in order to label it in the second element should also be able to identify the means to modify the equipment to reduce or eliminate exposure. Thus this third step should be able to mitigate many existing exposures. Many times it takes just as long to fix the problem as it does to obtain and apply labels.

The third hazard (skipping around here) is arc blast. Based on recent information, it is a little hard to quantify the minimum arcing current necessary to cause a significant arc blast but suffice to say that it exists. With arc resistant gear, the arc blast hazard is redirected and thus goes away with the doors closed and latched properly. With the doors open it dissipates to the point where it is not a significant hazard. If tripping occurs wihtin 1 cycle it is also unlikely to be a significant issue. In all other cases, stand to the side with the handle when operating equipment and use NFPA 79 (vertical or horizontal) handles, not IEC rotary handles.

The second hazard is arc flash. There are three concerns here and two approaches. The first is whether or not there is a significant arc flash risk in the first place. Under NESC, the answer is "yes" and arc flash PPE must be worn for pretty much all tasks. Under NFPA 70E there is a table for this when using the table approach. When using an engineering study, a risk assessment using one of the risk assessment standards (I suggest CCPS LOPA due to compatibility with the hazard and tasks) should be used. Finally the hazard assessment must be done. If using NFPA 70E tables, then the tables are used. If using the engineering study approach, a short circuit study, coordination study, and arc flash hazard study must be done. This requires a lot of field assessment data. As with shock protection, rules and procedures are developed and mitigation is highly recommended.

With the engineering study though there are two approaches. The first calculates everything down to a fine degree of precision (accuracy is limited by the available testing/development information). The output is a value such as "11 cal/cm^2". However the second approach simply looks at boundary conditions. If we are only going to issue say 4 cal/cm^2 and 40 cal/cm^2 PPE (common choices), then we really only care if the incident energy is <1.2 cal/cm^2, 1.2-4 cal/cm^2, 4-40 cal/cm^2, or over 40 cal/cm^2. However since the software used to produce the first two studies automatically calculates the third, not much time is saved. Significant time/money is saved by using the 70E table method but there are two caveats to it. First, actual "field testing" (analysis of incidents) shows that it is only effective 50% of the time vs. a calculated success rate of 95% for the engineering study approach and a "field testing" success rate of 100%. Second the key piece of information needed to verify that the table approach works (the trip time) essentially requires the same data necessary for the engineering approach so that the tables in practice are only useful if NO informaiton is available at all and it's at best, a good guess that works 50% of the time. Otherwise, the effort to achieve the 100% success rate is miniscule.


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: Two Category System
PostPosted: Mon Mar 16, 2015 10:47 am 
Offline

Joined: Mon Feb 22, 2010 10:24 am
Posts: 21
The two category system is not a method to analyze hazard levels (incident energy). It is a method for providing PPE in two different ratings rather than multiple PPE configurations. The hazard level must be determined at each location to know which level to utilize. Furthermore, if you do not perform the incident energy calculations you do not know which locations exceed 40 calories. It is not a substitute for calculating incident energy.


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: Two Category System
PostPosted: Mon Mar 16, 2015 3:06 pm 
Offline
Sparks Level

Joined: Tue Jan 19, 2010 2:35 pm
Posts: 96
This approach has been tried in the past, and based on feedback I've heard from the manufacturers who tried the cheaper option, it's not effective.

Here's an example of what I was told. "We can't do effective troubleshooting because we have to wear all this gear. Our guys are frustrated that they have to suit up just to . . . " One manufacturer had several smaller VFDs used in their manufacturing. Most of these were 10 HP or less, yet all the VFD's were labeled Category 2. They had us perform a full arc flash hazard analysis and most of the machines labeled Category 2 were really Category 0. However, we found the opposite as well. There were 3 switchgear and all calculated at over 40 calories @ 18", yet they were labeled Category 4.

Of course, there's no one size fits all answer. Each facility is unique, as is deciding how to spend your funds on safety. I'd ask that you consider the costs of just one arc flash accident against the money saved. Then I'd ask you to consider testifying before a jury as to why you chose the cheaper option.

However, the fact that you're asking questions says something about you and your company. I suspect you will go with a real study and not worry if you're complying with the NFPA 70E. Please remember, getting an arc flash study alone does not meet the Standard. There is much more to do.


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: Two Category System
PostPosted: Tue Mar 17, 2015 3:21 am 
Offline
Plasma Level
User avatar

Joined: Wed May 07, 2008 5:00 pm
Posts: 711
Location: Rutland, VT
EWB Engineering wrote:
We have a proposal from a vendor that will deliver a two category system (4&2) that is much less expensive than a full arc flash analysis. How is the assessment for a two category system completed vs a full assessment?


I would like echo others responses based on many years of experience. Is it correct that this vendor is a PPE vendor and not an engineering/safety firm? If a PPE vendor, then they are just selling you PPE without knowing what the incident energy levels are in your facility. This is an easy way to make a sale as it looks like they are doing you a favor by reducing levels. If you do an actual study, you may find that the incident energy levels are low for the equipment that is typically worked on (i.e. not the main switchboard but machine disconnect switches). You may only need actual AR PPE in limited areas.

I would spend the PPE money getting a actual study done. An actual study done properly has huge benefits.

Utilizing a commercial software program (EasyPower, SKM, etc) will provide a number of advantages, such as:

ability to easily run multiple scenarios and compare results for worst case scenario
ability to change protective device settings, particularly instantaneous settings on circuit breakers, to see if the incident energy can be reduced.
ability to change fuse types to see if the incident energy can be reduced. For example replacing a 400A Class RK5 fuse with a 400A A6D fuse.
ability to create one line diagrams as many facilities do not have updated drawings
ability to perform a coordination study at the same time and generate Time Current Curves
ability to perform a short circuit analysis and identify any over dutied equipment
ability to model the utility protective device to determine incident energy at the first connected device on transformer secondary side.
ability to incorporate changes to the facility to generate a new arc flash report

All this will enhance the safety of your facility.

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


Top
 Profile Send private message  
Reply with quote  
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 6 posts ] 

All times are UTC - 7 hours


Who is online

Users browsing this forum: No registered users and 4 guests


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