NESC studies greater/less than 1000V

Hello,

I am new to the forum. I have conducted many arc flash studies for industrial clients in the past. I am now beginning work on my first for a Utility based on NESC requirements.

NESC 410 states "The effective arc rating of clothing or a clothing system to be worn at voltages 1000V and above shall be determined using Tables 410-1 and 410-2 or performing an arc hazard analysis." Most of the analysis involves 12.47kV distribution circuits, switchgear and padmount transformers. For those areas I am going to conduct a engineering study based on IEEE 1584 calculations to determine the incident energy. NESC 410, Exception 2 states "For secondary systems below 1000V, applicable work rules required by this part and engineering controls shall be utiliized to limit exposure. In lieu of performing an arc hazard analysis, clothing or a clothing system with a minimum effective arc rating of 4 cal/cm^2 shall be required to limit the likelihood of ignition." Based on my experience with conducting arc flash studies for industrial clients I know the IE levels and PPE required at <1000V can be much higher than the arc rating of 4 cal/cm^2 the NESC requires. What has been the approach of others for areas less than 1000V? Have you conducted the full blown engineering study or have you simply required workers to wear clothing with ratings of 4 cal/cm^2?

All of the workers that could be exposed to hazards are experienced linemen with several years of experience and are exposed to constant training. I believe the NESC, NEC, NFPA, and OSHA would determine these employees as "Qualified Workers".

Any thougts??

Steve,

Welcome to our state of Confusion!

I agree with all you say except that I do not plan use 1584 for the overhead 12.47 kV and up distribution analysis. We are using ArcPro for those portions of the systems especially since ArcPro seems to be the basis for the calcs in Table 410-1. I am still in some of a quandry about the gear/transclosures/padmount...etc. issue though. I too believe that calcs for the <1000 volt portions are more necessary than for the >1000 volt areas. I am not comfortable at this point with just putting workers in 4 cal. clothing per the NESC.

They would definitely be termed qualified personnel, but we do make mistakes on occasion.

Alan

Thanks for the reply Alan! I'm debating between purchasing the ARC Pro software or sticking with the software my company uses (EDSA). I've tested EDSA against the Duke software for voltage less than 69kV they are very close. Over 69kV the reults don't make much sense to me.

I heard from SKM that in their next release they will include a NESC calculation output option similar to how you can choose between IEEE 1584 and NFPA 70E.

Here's a few more items to bounce off everyone regarding NESC arc flash studies:
Do you provide the approach boundaries and flash protection boundaries on the labels? Instead of a Hazard Risk Category (0,1,2,3,4) on the labels are you using the 4-cal, 8-cal, and 12-cal systems per Table 410-1? Are you applying the lables to outdoor padmounted gear? How are you handling the labeling for overhead distribution? What about outdoor substation disconnects, voltage regulators, breakers, etc.......

Lot's of questions I know.......................Any and all thoughts are greatly appreciated!

Steve

The utility I represent will not be using labels to identify the hazard at a given location.

For most utilities this would be impractical due to the very large number of locations involved.

In addition, utility systems are dynamic in that the source and circuit configurations may and do change (even from day to day), which will impact the value of the arc hazard at a given location.

We are still determining our approach and are participating in the two EPRI studies (transmission and distribution systems)

Arcpro for systems > 1000 volts (use the table since it reflects Arcpro results) and IEEE 1584 <1000 volts. The 4 cal exception is poor advice and will be changed either in the next code cycle or sooner. Arcpro tells you how to handle multi-phase or arc in a box situations. If you don't normally do utility work get someone who does, otherwise you'll make mistakes that you won't be able to recognize.

Tables in the NESC

Sorry, but I do not agree with using the tables in the NESC as they are extemely coarse and do not do a good job of modelling a system. I do agree that the 4 cal stuff for <1000 volts should not be used!

Alan

01/01/09

For Jim,

Would be interested on hearing your thoughts on the "deadline". I know of one major NC IOU that is taking the position that they only have to start by then. I also understand that APPA has asked the NESC folks for a clarification on the intention of the 01/01/09 date.

After all it only says "is performed" not is or has been completed

Thanks,
Alan.

NESC Update on 4Cal/cm^2

I heard at a conference that there was a update to the 4 Cal/Cm^2 value in NESC. Is this published and has anyone else heard about it?

As far as Arc Flash boundaries, we are including it because I am pointing out if they would decide to hotstick and they are beyond the boundary then they are ok in 1.2 Cal/Cm^2. I do not believe they are required for utilities (thanks Jim), But I think they are good information, it is important to point out how fast the incident energy goes.

One last point, has anyone addressed face protection with utilities. I am getting a lot of push back on face shields but an 8 cal blast would be VERY dangerous for lungs!

Show them this 8.4 Cal/cm2 arc flash, might change thier thinking

http://www.youtube.com/watch?v=Sw3n89Ml73A

Only the Employer can deem an employee "Qualified" , no one else can, but you had better be able to justify it (In my experience, most linemen know more and are safer than the rest of the electrical world, but there are exceptions)

Thanks Zog. I find those videos very useful in getting my point across. I hadn't see this one. When I have presented I have told the audience to go to youtube and enter arc flash. There are a couple good ones with interviews of survivors of acidents too.