Looking for opinions on this.
Our facility has a lot of variable frequency drives that are mounted on the walls in our motor control center rooms. Drives are 480vac and range from 1/2HP to 75 HP. Larger than 75 HP is typically mounted inside the MCC so I am not referring to those. All of our drives are fed from a disconnect in the MCC and are protected with current limiting fuses.

Rather than performing the study down to each drive and having to place an Arc Flash Warning sticker on each drive - would it be acceptable to do the following:
Have the electrician go back to the MCC where the drive is fed from (this info is clearly labeled on the drive and is usually in the same room) and look at the HRC level on the Arc Flash Warning label. Then reduce the HRC by 1 to determine PPE for working on the drive in question.
Comments and/or tomatos welcome.

I accidently got this thread in the wrong category. My apologies!

What is your basis of reducing the HRC by 1? Thats what you need to be prepared to answer after an accident.

Why do they need to be worked on energized? (That question will be asked before the above question). The goal of the 70E is not to tell you how to safely work on energized equipment but rather to discourage energized work and make the employer justify it.

If you are looking for a shortcut put the same label on the drive as is on the MCC feeding it to meet the labeling requirements.

You shouldn't just reduce by '1'. First off, if your Mcc LINE side is breaker fed, and the VFD's a fed via a FSD with current limiting fuses, I think you will probably be able to reduce by more than 1. Current limiting fuses below 200A tend to have similar clearing times, all being relatively fast. What I would do is 'model' your overall install. For example, take you largest, your smallest, and one in the middle. Do an IE calc on all. Take the highest value as the label for all VFDs. Use judgement if you have something out of the ordinary, like a 1000ft feeder versus a 200ft average. I think you will find that CURRENT limiting fuses in this range, will generally always be in the instantaneous response range with all fault currents.

Simplicity. Not enough hours in a day with trying to keep up with my actual job and trying to fit this in the "spare time". The HRC in 2009 NFPA70 table has a note (I don't have the actual note#) that the Category can be reduced by 1 if current limiting fuses that are operating in the current limiting region are used. I am trying to combine the study info with the table for simplicity.



I never mentioned anything about performing work while the drive is energized. Are you saying that an arc flash hazard not exist when the cover on the drive is on? It is a cheap flimsy piece of plastic held by one screw. A variable frequency drive can lose its smoke just like a MCC can.


I am looking for shortcuts and we need to work with the electricians so that they are able to work with the least amount of PPE that is allowed.

I am fighting 2 groups with this 70E stuff. Management who just wants it to be completed. Electricians who have been wearing category 2 clothing for years, always wear a switching suit and hood when operating mains and feeder breakers (they are happy with these, been doing it for years) but now have to wear a face shield for HRC1. According to some of the people on this forum they need to wear a face shield as they walk past an MCC with a HRC1 to go wherever it is they are going because the cover being bolted closed offers zero protection.

If I was a consultant who performed a study and dropped off the results and wrote their Safety Procedures policy and left - this I could do. The problem is working with journeyman electricians who have been safety smart through the years and trying to have them wear PPE that they do not think is necessary.

You need to to an analysis of fault currents and arcing currents to determine if the fault levels will be in the current limiting range. There is nothing simple about the task you have been given to do "in your spare time" tell your boss to get a qualified consultant or allot you the time to do this right.




I know you didnt, just asking if that was the case.



Not at all, in fact if you look around this forum you will se I am the one always pointing out that energized conductors do not need to be exposed to be a major arc flash hazard, too many people think that if the equipment is enclosed in something other than an ANSI arc rated enclosure there is not a hazard.



You either get shortcuts with the max PPE (Even that may not protect your workers) or you do it right to get the most accurate (Notice I did not say "minimum") PPE to do energized work. You want a shortcut? Ban any energized work at your facility (Of course you still need to wear the right PPE to prove it is de-energized)



Welcome to what will be know in the future as the "70E wars". Educate management, make sure they know it is thier responsibility to qualifiy the employees, authorize any energized work, etc.... Inform your electricians that the 70E commitee figured out that your face can get burned just as easy as your torso (Duh) so they added the facesheild requirement to HRC 1 and buy them some good ones. Tell them to keep up the good work. I have consulted hundreds of large companies (The ones you buy stocks in) over the last 10 years on 70E compliance, and you are having the same issues they all have, I know what you have been tasked with and have seen many people put in your same situation. Trust me on this, you need to educate management.




I dont think anyone (Anymore) here thinks that, but the covers can not be counted on to offer any real protection. The 70E is clear on when a hazard exists, interaction with equipment. Could a MCC blow up as someone walks by and casue them to be burned by an arc flash?, sure it can, just happened to someone I know (Feel free to PM me if you want to call him and ask about it), but is there a risk high enough that PPE should be worn to walk past a MCC?, not IMO. You have to draw the line on risk vs hazard somewhere.



Hmm, tough to do, those old timer electricans that have been lucky for 30 years are the hardest to change. Get them some quality 70E training, not these cheap out of the box courses or "Free" seminars from someone trying to sell you something. Or go to http://www.westex.com and download the arc testing videos, show them what a 5 cal/cm2 arc flash looks like, might change thier thinking. Give them a tour of a burn unit, so they can see what pain is all about.

I just checked out that URL but the site isn't there anymore. Do you know of anywhere else I can take a look at the videos that you have mentioned.

Sorry, wrong link

http://www.westexinc.com/

I would be very careful about making such assumptions for 2 reasons. The further away the VSD is away from the MCC the lower the bolted fault current and the more likely that the arcing current is lower than the instantaneous pickup of the protective device characteristic. Secondly at 75HP the motor contribution will actually reduce the current seen by the protective device even further and you will have a double whammy of additional arcing current (increased Incident Energy) and insufficient device current to quickly disconnect the fault.

If the 75hp motor is being fed with a VSD, the motor under a fault will not produce current into the fault on the line side of the VSD, unless there is a solid by-pass.

Usually VSD protected using current limiting or high speed fuses (more expensive, but much faster than current limiting). All well-known VSD manufacturers publish tables with the recommendations how to achieve Type 2 protection (no damage) or Type 1 protection (all violence should not go outside of the enclosure). So, you’ll probably don’t need to label your VSDs.

Also, the whole idea of arc flash study is not just to label the equipment. It is more cultural and administrative issue – how to push the employees to use PPE (your PPE plan should include both arc flash clothing for everyday use and for special locations/situations), follow safety procedures, lockout/tagout … My suggestion is - do not over-label your facility. More labels doesn’t mean more safety. Multiple labels increase risk of error. Also, labeling every piece of equipment actually minimizes the urgency of the warning.

Usually VSD protected using current limiting or high speed fuses (more expensive, but much faster than current limiting). All well-known VSD manufacturers publish tables with the recommendations how to achieve Type 2 protection (no damage) or Type 1 protection (all violence should not go outside of the enclosure). So, you’ll probably don’t need to label your VSDs .
Also, the whole idea of arc flash study is not just to label the equipment. It is more cultural and administrative issue – how to push the employees to use PPE, follow safety procedures, lockout/tagout … My suggestion is - do not over-label your facility. More labels doesn’t mean more safety. Multiple labels increase risk of error. Also, labeling every piece of equipment actually minimizes the urgency of the warning.