Problems with NFPA 70E and IEEE 1584 1

[Electic]

I have worked on a large installation with state of the art software, and compared results with three other, eminent engineering companies. The following do not constitute questions so much as observations of some of the inconsistencies and challenges arising from trying to apply the above guides and codes in a meaningful (not just academic) fashion.

Commentary and dialogue is appreciated. Please reference the following numbered paragraphs or add new numbers for additional concerns.

1) Responsibility is not clearly delineated between the journeyman, his employer or the site owner. This is not a large concern and does not prevent us from applying labels.

2) NFPA 70E prescriptive tables include a range of risk category PPE requirements for identical equipment, depending on how involved the described work will be. It is understood that some weighting factor combined with industry experience has been applied to achieve these results. This mechanism is not available in the calculation methods, and though the principles are understood, the liability of adjusting risk categories apart from the given calculations is more than any firm would choose to use. The result is overprotection that might not be followed. This is a medium concern, but does not prevent us from applying labels, but does hamper administrating a safety plan.

3) IEEE 1584 can generate unlikely results such as quarter mile safe approach distance to a regular 480V transformer. The given remedy is to limit clearing time to 2 seconds. This type of patch calls into question the reliability of the calculation. This is a large concern in the context of item 4 below.

4) IEEE 1884 calculated arc flash exposures do not converge with predictable results. This is acknowledged in NFPA 70E, but no real world solution is suggested. For example, increasing fault current may either reduce or increase exposure depending on many other parameters. These calculations have been defended as the best empirical results available, but that is not good enough, the industry needs to perhaps compromise the results a little bit to make the results predictable or this whole thing remains an unmanageable liability.

For example, we now get differing calculated arc flash exposure based on FUSE manufacturer (of 100E type fuses). It is unreasonable to inventory equipment to that level of detail, yet failure to do so may constitute a liability. Seeing how particular the calculations are, it seems the greatest influence of calculated exposure might be arc resistance itself. This will be influenced on unpredictable atmospheric conditions, yet if the effect is to reduce arc current to just less than instantaneous pick up (many of which are being adjusted to reduce calculated exposure to workable levels) the resulting exposure could soar from Risk Category 1 to “Dangerous Unworkable”. This simple phenomenon seems to blow the whole theory. In discussion I have been told that any analysis and PPE is better than before (true), however; imagine this getting into the hands of an aggressive personal injury lawyer. Am I overlooking something?

I feel the science behind the calculations should be tampered with to achieve consistent predictable results even if not quite as accurate.

 

[advidana]

Maybe you should also be sending these questions to the NFPA and IEEE committees.

 

[dpc]

There are certainly issues regarding the arc-flash safety standards. To further complicate matters, the new NESC uses a different computation method and bases all calcs on line-to-ground faults.

I would encourage you to pass you concerns along to the NFPA 70E and IEEE 1584 committees. Many of the concerns you raise have been discussed previously, but it helps to give them as much input as possible.

There is ongoing work on the IEEE 1584 equations and I would expect some significant enhancments/changes in the next revision cycle.

Regarding some of the specifics of your concerns -

1. The division of responsibility for safety must be established by the the owner. The owner must establish and then enforce the safety rules that will be used on site. NFPA 70E provides a model safety plan but it must be adopted by the owner before it anything more than a recommendation. OSHA will look squarely at the owner after any site accident.

2. 480V faults, especially at poorly protected transformer secondaries can have very high arc energy due to high currents and prolonged arc times. Just because we don't like the results or don't believe them doesn't necessarily mean they are wrong. Even if we question the exact results, it is clear that the calculations help us identify those parts of the system that are the most dangerous.

 

[Electic]

Thanks for the suggestions fellows, I will try to contact the committees.

in response to DPC comments (and I greatly appreciate the dialogue)

1) site owner being responsible only seems appropriate if the site owner has a maintenance staff. I sense an untested legal responsablity for facilities with substantial power density but no staff, such as a shopping center. I believe OSHA at that point would be looking squarely at the journeyman or contractor, yet they have little control over the installation and its history. That hasn't stopped us from performing analysis (where invited).

2) It is not a matter of 'not liking' the results, but rather, that of maintaining credibility. There is no way that I can tell a room full of journeymen that the minimum safe approach distance to a 1000kVA 480V padmount is a quarter mile (1320 feet), and expect them to believe the rest of the warnings. In such cases we have simply labelled the equipment "do not work energized".

The calculations are only for radiated arc energy(not projectiles or flaming oil) and I doubt that could be measured beyond several hundred feet.

 

[alehman]

I think your solution for item 2 is appropriate. I agree with dpc in that the calculated approach distance may indeed be valid, but in practice there is no safe approach distance.

I recently experienced an arcing fault at the unprotected terminals of a similar 480V transformer. It was quite a fireworks show. The primary fuses never opened and the arc burned until the utility company manually opened a breaker at the substation. One unfortunate worker who happened to be within a few feet was badly injured.

 

[resqcapt19]

NFPA 70E is in its 2008 revision cycle at this time. The closing date for proposals to make changes for the 2008 edition is 9/15/2006.

http://www.nfpa.org/aboutthecodes/AboutTheCodes.asp?DocNum=70E

Don

 

[dpc]

Contractors are definitely held accountable by OSHA for not providing adequate PPE or establishing and enforcing safety plans. If the owner has done a hazard assessment and put appropriate labels in place, I suspect you're correct that the contractor would be in the cross-hairs if there was an accident.

I agree that less information on labels may be better than more. Is it worth relabeling when another large motor is added and the arc-flash level goes from 8.2 cal/cm2 to 9 cal/cm2? If we just put the PPE level and a conservative hazard boundary on the label, I think everyone's life would be simpler.

 

[Electic]

Thank You Gents,

Comments have been sent to the apparent committee contact.

My experience is that many consultants offering Arc Flash Analysis do so with indifference to what the result might infer.

Regards,

GB

 

[resqcapt19]

GB,

Comments have been sent to the apparent committee contact.

For 70E you must follow the NFPA rules or the committee will not act on your comments. In general, you must supply specific wording for a proposed change. Just comments or questions are not acted on.
Don