|Arc Flash Forum
|Arc Flash Label Updating - How Many Times?
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|Author:||Jim Phillips (brainfiller) [ Sun Nov 13, 2016 9:23 am ]|
|Post subject:||Arc Flash Label Updating - How Many Times?|
NFPA 70E requires that an Arc Flash Risk Assessment be updated when a major modification or renovation takes place. It shall be reviewed periodically, at intervals not to exceed 5 years, to account for changes in the electrical distribution system that could affect the results of the arc flash risk assessment. Countries outside of the US that do not use NFPA 70E may have a similar label review/updating requirement.
NFPA 70E further states that where the review of the arc flash hazard risk assessment identifies a change that renders the label inaccurate, the label shall be updated.
What is the maximum number of times you have updated any arc flash label since first applied?
-Still have original labels
-Updated more than twice
-No labels yet
-I don’t do labeling
|Author:||PaulEngr [ Sun Nov 13, 2016 5:48 pm ]|
|Post subject:||Re: Arc Flash Label Updating - How Many Times?|
Previous plant has done arc flash studies for at least 15 years. During that time there have been several iterations since for instance the original study used the assumptions that have existed since the 1960's which means ignore cable impedance. Subsequent studies achieved a much more accurate model for the main distribution system (plant is a cogen so effectively is a private utility), refining the model for various areas to improve it with each iteration of the arc flash study. With 6 digit price tags what it comes down to is that although they would have loved to do a detailed and complete model, such was not within budget at each iteration. The worst one being the update done by Square D who changed project managers something like 3 times and had to start over every time because none of the survey/notes were passed on.
The other significant area is the mine which has about 150 pieces of equipment that all get moved about every 6-12 months. The distances are not small...longest is about 8 miles and shortest is about 2 miles from the main substation, substantially impacting available short circuit current across the site's 70 miles of overhead power lines. This problem even ignoring arc flash is so significant that MSHA has their own regulations for trip settings for portable power cables in underground and coal mines. Both the ampacity AND the distance both need to be used to determine trip settings, recognizing that tripping on a very long shielded cable is pretty unlikely if cable impedance is ignored. The intent is that the settings are checked/changed EVERY time a piece of equipment is plugged into the power center. The concern there is short circuits (either to ground or another phase). So far MSHA hasn't shown much interest in arc flash but the principle applies the same way.
So...for fixed equipment with one particular plant a lot has changed in terms of model accuracy and thus a lot of labels get changed during each and every 5 year update. But for mines in particular where there is no such thing as fixed equipment, realistically new labels should be applied just about every day or two, or else "boundary" labels (calculate incident energy for a variety of distances and cable lengths and choose the worst case) should be applied which at least cuts down on the number of label changes.
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