I'm using SKM software to run an Arc Flash study on an industrial facility.

On the secondary of a 13.2kV to 4160V transformer (6.3%Z), I have about 10kA of fault current available. After going through a S&C SMU-20, 200-Amp fuse, my Arc Flash Incident energy is down around 1.1 Cal/cm^2.

I'm not comfortable labelling any 4160V equipment as category 0. I was thinking of changing some opening times in my calculations to raise the category to at least a 2.

So my question is, what is the minimum Arc Flash PPE category that you would recommend for labeling on both 4160V and 13.2kV systems, even if the calculations show a lower value.

Thanks!
Mike

Ah, you've discovered the benefits of a high arcing fault current (assuming the 10 kA is arcing and not bolted) which will cause the protective device to clear rapidly, reducing the time which is a component of the energy formula.

I would not fudge the results to increase the category. Are there other areas, namely on a 480 V system, that the category is higher? What you could do is make a recommendation that the qualified electricians wear FR clothing that is a minimum of 8 cal/cm2.

I would label it HRC 1, just for a CYA thing, but that is just my 2 cents.

I generally convince the site to accept a general minimum PPE of Level 1 for all electrical work. I often calculate medium voltage equipment to have low IE values. But to keep everything consistent and not add confusion, on the Warning Label, I list the IE as 4.0 cals/cm2 and the PPE as Level 1.

Arc Flash is about protecting the person and not absolute mathematical correctness. In general I do NOT massage the numbers for IE as long as they are coming out at 4.0 or more. But when we have a site min PPE level of 1, I want the field label to coincide with the PPE.

This avoids confusion. A new contractor seeing a IE of 1.0 cals/cm2 and a PPE lEVEL OF 1, both on the label, may decide he knows better and that his Level 0 is adequate.

I have Level 1 PPE on most of my medium voltage gear. Amazing, isn't it.

Are you performing this study for a client, or is this an in-house study?

If the study is in-house, I would leave the values as are, but you could change it to a HRC 1. You can change the category level thresholds within SKM if desired so that nothing shows up as less than Cat 1. But document it, so that the next guy knows why.

If you are performing the study for a client, you should report what you find. Any changes should come as recommendations if you feel they are necessary.

All the decision regarding implementation are made upfront, before the analysis. The analysis is only a small part of the total. There is also training, policy, and auditing that go into the program. Most sites are prepared to go to FR clothing and don't want to accept Level 0 because its too hard to verify compliance. So if they want a Level 1 minimum, then I am NOT going to print a label that says IE=0.3 cal/cm2 with a min PPE=1. That doesn't make sense and is confusing. One site insisted on Level 2. Does it make sense to see a label with IE=1.0 cal/cm2 and PPE=2.

Again, the goal is to assure service personnel are in the appropriate PPE, not to prove how scientific the analysis can be. I am not going to let a contractor argue or debate that the label was wrong as IE 3.0 cals is Level 1 and not the Level 2 cited on the label.

The spreadsheet I developed allows you to input a PPE minimum. So the actual IE is in the spreadsheet, along with fault current, voltage, clearing time, 85% rule, etc. But if the IE calculated is less than the threshold for the min PPE specified, the program defaults the lowest value of that PPE level, ie, Level 1=4, Level 2=8, etc.

NFPA 70E-2009 requires only either the incident energy OR the level of PPE. Therefore, if a facility has determined that work will be performed in a minimum of Category 1 FR clothing, all equipment that is 4 cal/cm2 or less can have labels that just state "FR of 4 cal/cm2 Required at 18" working distance" for a 480V system.

The other approach would be to label what the actual IE is and then thru safety policy and training, all electrical workers are to wear a minimum of Category 1 PPE, even if the label states Category 0.

The first option would be acceptable, but the second one would just lead to confusion and introduces the possibility of some intervening interpretation. I think you are too hung up on the science and not appreciating the human aspect. Of what value would it be to have a label say 3.4cal and PPE 2. Is the electrician in the field going to use the actually IE to back calculate a change in distance? There is no downside to having the IE match the min PPE. The engineering dept has the spreadsheet with the actual IE calcs if they need them. Let them be changed under proper supervision.

JMO.

Mike can you tell me exactly what you intend to do at 4160 volts on energized circuits that will necessitate the use of PPE?

Mike,

Good question. My assumption was that the OP was only to test dead and ground and also for raking out and in circuit breakers. That work would have to done using PPE for an energize condition.

I also assumed that it was an industrial facility so there should be no energized MV work.

Another operation that is often performed live is phasing when you more than one supply source.

You can never avoid "energized work". Even if you shut power off and lock it out the act of verifing it is dead and applying protective grounds is "energized work"

Zog,

I understand that as stated in my sentence previous to that about testing dead and grounding is considered energized work.

My point was more that, as a utility, one is usually doing live 4160 V and that would most likely not be the case in an industrial facility.

This appears to be MV gear that this worker is racking a breaker in on, which is one of the most dangerous aspects of working on such equipment (when energized).

http://www.youtube.com/watch?v=yd4MFWc1ZwI