Under 2000 short circuit Amps at 208 V is now always Level 0? 1

[bdn2004]

This is a common situation at a Plant we work at. A small dry type transformer fed from a 480V panelboard, then feeds a 120/208V three phase lighting panel. The Lighting Panel requires an Arc Flash Label.

I've been told that since the Isc is less than 2000A it is only the minimum arc flash hazard - as it can not sustain an arc at that voltage and that low current. If that's the case...then why doesn't EasyPower correct this in the software? Seems it would be simple to do or give you an option - yet they don't.

How is this handled at your Plant?

 

[dpc]

First, NFPA 70E says that if you are basing your PPE requirements on the calculated incident energy (2.7 cal/cm2 here), then the PPE Category (as detailed in NFPA 70E for the Categories Method), should NOT be used.

Also, "PPE Level 2", based on on NFPA PPE Categories would start at 4 cal/cm2. The break points can be user-modified in the EasyPower library, so I assume this was a customization at some point.

Your thread title refers to "Level 0". There actually is no longer a PPE Category 0 in NFPA 70E.

This PPE Level display in EasyPower can be turned off in the Arc Flash Options (Advanced button). By default, it is not displayed.

In EasyPower and other software, the incident energy level can be manually set to any value for any bus. Also, just because IEEE 1584 says the risk is low below 2000 A of fault current, doesn't mean there is no risk. A common practice is to set all of these situations to 4 cal/cm2. This will put the worker in a reasonable level of PPE that should generally keep them well-protected.

Cheers,

Dave

 

[Kiribanda]

All calculation software like EASYPOWER, ETAP etc. are just "TOOLS" doing complex calculations for you.
Based on the results you have to use your engineering knowledge & judgement to make the conclusions.

 

[bdn2004]

dpc,

Thanks for the thoughtful answer.

The Plant we work for designed their own AF label and have their own AF standard. Instead of looking at the IE it's easier for them to standardize on 3 different levels to tell their contractors and workers what PPE is required.

The 3 Levels are:
a) less than 1.2 cal/cm^2 = Level 0, minimum PPE
b) between 1.2 and 12 is a Level 2, all PPE must be rated minimum IE 12
c) 12 to 65 is Level 4 and 65 PPE is required in this range
d) Above 65 that is Extreme Danger.

That PPE that Level and IE is sewn into the clothing and is outwardly visible. I can see where this might be a little confusing for someone familiar with the standards and working on other plants sites.

But the 208V, 2000A question....it's not in their AF company standard. And you are saying IE = 4 is what you've seen...a 4 would fall in the Level 2 for this Plant. So to me it makes sense to leave it how Easy Power calculates it.

 

[bdn2004]

Kiribanda,

Don't take this as an offense...

But in my experience it is way better to have a backed up sound reason as to why you did something as opposed to just using your own engineering judgment and experience. Most things aren't just a matter of your opinion.

If this Plant, who writes their own standards, wants to do it differently than how the software we are under contract to use calculates it - they can write it into the standard: Rev 1. Then we are on the same page.

That's why you write standards.

 

[dpc]

bdn2004,

It seems they have a "site specific" PPE designation as defined in NFPA 70E, so no problem, as long as they are consistent. Not what I'd recommend, but nobody asked me.

Use of 4 cal/cm2 PPE for 250 V and below is basically consistent with the Category method in NFPA 70E, as well as the NESC. By jumping to 12 cal/cm2 PPE, they are will likely be overdressed, but I assume they can get to 12 cal/cm2 using a face shield (and balaclava) and not arc suit hood. Personally, I would not be comfortable saying there is NO risk and that NO PPE is required. IEEE 1584 is not a safety standard, but simply a calculation method. Even when the arc is not sustained, molten metal is ejected from the arc source, and some protection is needed. There is a lower limit to the application of the equations in IEEE 1584. From 208 V to 600 V, the lower limit is 500 A. Below that, EasyPower probably doesn't give you a result. For 30 kVA and larger xfmrs, the fault current at 208 V should exceed 2000 A in most cases. It's all pretty low risk, but not zero risk. At 480 V, it's another world.

Dave

 

[mparenteau]

Not to over-complicate matters, but I would say the PPE level depends on the task. If you are just throwing breakers as an example to lockout and tagout, covers are on, 208V system, etc., and you are below the 2000A threshold: then no PPE needed (the panel provides containment). If covers are off, and you are working on an energized circuit then PPE is warranted as suggested by dpc.

Mike

PS Should add that PPE "go / no-go" decisions based off of risk assessment.

 

[alehman]

NFPA 70E (2021) Table 130.5(C) provides guidance on the types of tasks and conditions that may or may not require PPE.

Alan
The engineer's first problem in any design situation is to discover what the problem really is. Unk.