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 Post subject: 2018 NFPA70E - condition of maintenance
PostPosted: Wed Mar 07, 2018 1:18 pm 

Joined: Wed Oct 01, 2008 6:05 am
Posts: 27
Have you had discussions about this excerpt in the 2018 NFPA70E?

130.5 (G)
“The incident energy analysis shall take into consideration the characteristics of the overcurrent protective device and its fault clearing time, including its condition of maintenance.”

How can software calculations be modified to include the condition of maintenance?

Thank you!


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 Post subject: Re: 2018 NFPA70E - condition of maintenance
PostPosted: Thu Mar 08, 2018 2:22 pm 
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uriah1 wrote:
Have you had discussions about this excerpt in the 2018 NFPA70E?

130.5 (G)
“The incident energy analysis shall take into consideration the characteristics of the overcurrent protective device and its fault clearing time, including its condition of maintenance.”

How can software calculations be modified to include the condition of maintenance?

Thank you!


Short answer: you really can't. This has absolutely nothing to do with a software calculation. This is where a different procedure such as ANSI RIA R15.06 or the AiChE LOPA or HAZOP, or SWIF, or IEC 61511 methods of risk assessment come into play. The ANALYSIS should take it into consideration. It's not a number. It's the engineering side of it (making judgements). It includes a whole separate set of training and certification that has nothing to do with any IEEE standards. There is software out there to help drive the process but frankly I've used it and for this specific use, it's not much help. Even doing for instance fault trees, I can do them on a white board faster and easier than using software.

You can still get a result if you were to consider the result if the overcurrent protective device fails altogether (replace the overcurrent device with a section of bus and see what you get). This allows you to run the calculation with the next upstream device operating instead. Or to simplify things, simply recalculate using 2 seconds. Since incident energy is linear with time, it is very easy to do this with a calculator or a spreadsheet. Of course you can then consider a 2-level failure as well but at some point probability plays a role. So this quantifies the hazard if the breaker for instance fails but it does nothing in terms of the real issue.

Consider the fact that everything in IEEE 1584, NFPA 70E, and all other standards assume that the equipment is working as expected. In reality they all allow for a single fault condition. This means that for instance if a piece of equipment is faulty and needs repair, then the assumption that everything upstream of it is in good repair. So we isolate the equipment using the upstream device (along with testing for absence of voltage) and then commence to making repairs. But what if the upstream device is faulty? Then we go upstream again. What if that one is faulty? Then we go upstream again. What if we get to equipment that is functioning but now we have to consider backfeeding power from more than one source of faulty equipment? You can quickly see where this is going particularly in some plants that are poorly maintained. Simply put, there is no standard for maintaining equipment that is not properly maintained at all. It's just too unpredictable what could happen. Instead the standards are based on equipment that is performing to some sort of "average" so that things happen predictably. There are standards for doing this kind of analysis called Markov modelling or the simplified version which is fault tree analysis but it takes a lot of experience and knowledge to successfully use this sort of analysis and it is way beyond the scope of NFPA 70E. Hence the reason that it is not even mentioned.

Remember that no matter how 70E phrases it, what OSHA expects is a risk assessment. When doing risk assessments, there are three considerations. The first is the magnitude of the hazard. The second is the risk or the likelihood that an injury will occur due to the hazard. This aspect must consider the tasks to be performed, the condition of the equipment, and so forth. For instance the 70E Committee has several times in response to proposals stated that "just walking by" is not an arc flash hazard. They have also made a similar statement in an informational note with regards to MCC's. The definition of an arc flash hazard states that it must include some sort of activity which is LIKELY to cause an arcing fault.

For instance if I pull out my Craftsman mechanic's screwdriver and attempt to tighten a screw on a sheet metal panel while reaching over the top of an energized bus, there is a pretty good chance that at some point I'm going to drop the screw driver or lean over too far and cause an arcing fault. On the other hand if I do the exact same exercise except that first I take a piece of rubber roll blanket material and attach it with nonconductive clothes pins and even use a 1000 V insulated screw driver where the exposed tip is less than the insulation in the gear, there is virtually no chance of an arcing fault occurring while performing the exact same task.

Fortunately risk with electrical equipment is almost a binary decision. Either the hazard is too small to be a major concern, or it isn't. Second either the task almost invariably involves either a reliance on human error or it relies on proper functioning of properly maintained equipment. With regards to the former, human error under the best of circumstances is around 1-10%, and given the hazards involved safety standards require a significantly lower probability of error than that. When it comes to equipment, generally speaking well maintained electrical equipment is not inherently dangerous. But if the equipment just faulted such as a circuit breaker or fuse trip, then that is no longer the case. NEMA AB-4 states that a molded case breaker must be visibly examined for evidence of damage before it can be put back in service and OSHA requires that the source of the fault be determined before the equipment can be put back in service. I can cite numerous examples of where this was not done and negative consequences including arc flash victims occurred. Also any time that the equipment relies on human performance, there are frequently failures. For example trying to insert an MCC backet back onto an energized bus after it is removed is heavily reliant on the person inserting it for proper alignment. Numerous arc flash incidents have occurred from this practice. Similarly on some types of switchgear the process of racking (inserting) a breaker into an energized cell has ended in arc flash more than once. This is very different for instance from opening or closing a disconnect switch or a breaker that has a spring loaded or overhung cam mechanism that controls the motion of the power contacts and removals human error entirely from it's operation under normal conditions.

The third and final step is to consider mitigation efforts. This means that we want to find ways to eliminate the hazard such as what I just described (or better yet, just kill power), or to lower the hazard such as making adjustments to breakers so that it trips fast enough to lower the arc flash hazard significantly, or as a last and final resort, use PPE. If PPE is used then we have to consider what would be considered adequate PPE and Annex H helps with that. ANSI Z10 (Hierarchy of Controls) clearly states that PPE is the last resort. This is one of the big problems with 70E in the way that it is written...it essentially focuses entirely on PPE as a solution because it doesn't include any aspect of risk assessment except for the tables in Article 130. However that does point to a possible simplified way out. Now as of 2018 the tables are broken down into 3 sections: risk assessment (the first table) based on the task, hazard assessment based on the equipment (the second table), and PPE assessment. There is nothing in 70E that precludes a risk assessment study from simply ADOPTING the first table and the substituting other results from the second and third tables. There is a prohibition in the Code about mixing the engineering approach and the table based approach but obviously if we simply borrow from the first table and validate it within the risk assessment engineering study, then there is nothing to preclude this "borrowing". Another similar table exists on OSHA 1910.269 Annexes and frankly it's a better table than the one in 70E.


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 Post subject: Re: 2018 NFPA70E - condition of maintenance
PostPosted: Mon Mar 12, 2018 8:49 am 

Joined: Mon Dec 07, 2015 9:45 am
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Location: Massachusetts
Our plan is the use of the "Fail to Operate" option in SKMv8 for any protective device that fails the device evaluation as well as any device that our field investigation team identifies as likely to fail to operate due to concerns of condition. Since part of our business is electrical maintenance our crew is well versed in how to assess the condition of equipment and part of our field investigation portion of studies has always been to report back on equipment condition for our sales team's use.


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 Post subject: Re: 2018 NFPA70E - condition of maintenance
PostPosted: Mon Mar 26, 2018 5:10 am 

Joined: Fri Nov 06, 2015 1:05 am
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Location: Evansville IN
I think using the risk assessment approach with a valid study is the best way to work the situation. I am currently working with some of our Maintenance Teams on developing a risk assessment . We are currently attempting to service our MCC's in the plant (approx. 100). We have never done maintenance on this equipment. We do have a valid study's for up-stream breakers. As of this week; The first breaker and MCC that was inspected, showed abnormal signs with dripping oil and no record of maintenance. The study showed a level 1(2.1cal) at the top of the MCC breaker, we still chose to de-energize up-stream breaker based on "no maintenance" of the MCC main Breaker or cubicles. This is a dynamic situation where Team Members are asking for Yes or No on servicing these MCC's. They want to be told a solid single answer. I am attempting to move the Team to a risk assessment approach. They are learning what NFPA 70B is and appreciate the work done on all the NFPA standards. I hope that we could have an industry standard risk assessment.


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 Post subject: Re: 2018 NFPA70E - condition of maintenance
PostPosted: Fri Mar 30, 2018 4:24 pm 
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downriverbill wrote:
I think using the risk assessment approach with a valid study is the best way to work the situation. I am currently working with some of our Maintenance Teams on developing a risk assessment . We are currently attempting to service our MCC's in the plant (approx. 100). We have never done maintenance on this equipment. We do have a valid study's for up-stream breakers. As of this week; The first breaker and MCC that was inspected, showed abnormal signs with dripping oil and no record of maintenance. The study showed a level 1(2.1cal) at the top of the MCC breaker, we still chose to de-energize up-stream breaker based on "no maintenance" of the MCC main Breaker or cubicles. This is a dynamic situation where Team Members are asking for Yes or No on servicing these MCC's. They want to be told a solid single answer. I am attempting to move the Team to a risk assessment approach. They are learning what NFPA 70B is and appreciate the work done on all the NFPA standards. I hope that we could have an industry standard risk assessment.


There are about a dozen industry standards for risk assessments. But you need to consider which one works best. For instance the ANSI .TR3, RIA, and IEC 61508 standards don't really apply because they are designed around moving equipment like assembly lines. These standards deal with moving equipment where for instance one of the issues is how many times per hour or per minute an operator is exposed to moving equipment, the likelihood that they can get out of the way if something happens, and whether the injuries are simple first aid cases or maybe require more than one doctor's visit. It can work for electrical hazards but it's like trying to fit a square peg in a round hole.

I suggest considering AIChE LOPA instead. This standard is designed around hazards that happen rarely, where the hazard usually results in hospitalization or one or more fatalities, where usually it happens so fast that there's no way of getting out of the way. The one downside is that the standard has a lot of focus on bad stuff that moves in pipes, pumps, and tanks, but they've included maintenance hazards as well since it is a general standard for process industries. It is almost tailor made for considering risk assessments for arc flash and shock hazards. LOPA also has the advantage that it's already an established standard with plenty of training, certification, and industry and government support behind it.


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 Post subject: Re: 2018 NFPA70E - condition of maintenance
PostPosted: Fri Apr 26, 2019 9:07 am 

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PaulEngr wrote:
I suggest considering AIChE LOPA instead. This standard is designed around hazards that happen rarely, where the hazard usually results in hospitalization or one or more fatalities, where usually it happens so fast that there's no way of getting out of the way. The one downside is that the standard has a lot of focus on bad stuff that moves in pipes, pumps, and tanks, but they've included maintenance hazards as well since it is a general standard for process industries. It is almost tailor made for considering risk assessments for arc flash and shock hazards. LOPA also has the advantage that it's already an established standard with plenty of training, certification, and industry and government support behind it.


PaulEngr, I work in a chemical plant. We use LOPA in our safety instrumented systems (SIS), but I know very little about it beyond that. I haven't thought about using it for OCPD maintenance. Do you have any specific examples of LOPA being applied this way that you'd be willing to share? Thanks.


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