ARC Flash Study

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I've never been required to do an arc flash study from the local AHJ. It is not in their scope. They could require the general sign from 110.16, but that does not require calculations.
It is OSHA, employers and the building owner that could require it, and they do when work will be done while equipment is energized.

Mr. Bill, not to hijack the thread, but what kind of calculations are you providing to establish the GFP setting?
 
Hijacked thread

Hijacked thread

I had read somewhere that 200,000 Amp-cycles is a recommended maximum for tolerable fault energy.

I start with the calculated phase-to-phase fault energy and divide by 3 to determine the maximum ground fault. (Some argue to divide by the square root of 3).

So then I use the 200,000 Amp-cycles / max ground fault = max cycles

Example: Calculated 19kA for the AIC.

19,000 Amp / 3 = 6,333 Amp for ground fault

200,000 Amp-cycles = 31.6 cycles
6,333 Amp

Maximum GFI setting of 0.5 sec. If there's another GFI downstream then it has to be 0.3 sec or less to maintain the 0.1 sec gap between devices. (Since the trip curve has a width) This was the first time I was asked to do this calculation so I'd like feed back about my methods or assumptions.
 
The NEC permits 1200A max., so 6,333 will not satisfy code
In critical environments, I set them at 1200A for max permitted delay.
In not-so critical environments, I choose 20% of the phase trip or 1200A whichever is less.
 
..ron>?

..ron>?

Why choose anything less than 1200 amps for the gf setting? thereby letting any downstream device have a better chance to operate?
JM
 
zog said:
We have done many in Michigan and Ohio, seems the EI's are requireing it be done in many areas
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under what authority would an EI have to require such a thing? there is no code requirement involved.
 
110.16? I am not an EI, if a contractor calls and wants an arc flash study done to satisfy the inspector what am i supposed to say? As I understand EI's can interpret requirements however they want to.
 
Arc Flash Studies are not required if the owners safety plan says that no equipment will be worked on live.

The AHJ can only enforce the NEC portion for proper labeling. He could I suppose notify OSHA, and have them come out, but the Owner simply puts in writing that the equipment is not going to be worked on live. May not be necessarily practical, but it is one approach.
 
zog said:
110.16? I am not an EI, if a contractor calls and wants an arc flash study done to satisfy the inspector what am i supposed to say? As I understand EI's can interpret requirements however they want to.
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That is just plain false. They can only require things that the local electrical code requires. Anything beyond that is not within their authority to require. Sometimes they are little tyrants that demand things that is outside their authority and it may be easier to comply rather than fight it.

I don't blame you for accepting work that falls out of the sky on you.
 
ron said:
The NEC permits 1200A max., so 6,333 will not satisfy code
In critical environments, I set them at 1200A for max permitted delay.
In not-so critical environments, I choose 20% of the phase trip or 1200A whichever is less.
Click to expand...

The 6,333A number was used to determine the maximum time delay for the GFI, per 517.17(C). I actually had the amp setting of the GFI at 25% on a 1600A service. This was done per literature supplied by Eaton (2006 Consulting Application Guide) which recommends 20-30% of overcurrent protection. Page 1.4-6.
 
Typical arc flash studies (including our industrial site) will include all substations 208/120V and above, and with transformers sized at 125kva and above.
 
necnotevenclose said:
Has anyone been required to do an arch flash study based on a local AHJ?
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Arc-flash study would and should not be in the scope of an installation contractor so the AHJ could not require it from them. Should an EC wish to venture into the design-build area of the business, he better retain a PE and all that comes with it.

The AHJ can require the Owner to retain the services of an Engineering firm to perform such studies. This of course would be applicable to larger commercial and industrial facilities and/if the service exceeds 208V or 112.5kVA transformer supply.
 
"It would be anything that might be worked on or near while energized."

Remember that includes switching. And over 50 volts to ground.

"Would an ARC flash study include an entire system from a 2000A 480V switchboard down to say a 208V 125A loadcenter?"

Ours goes from the utility all the way down to each motor or transformer or panel board. We even had the utility change the fuses on the transmission lines to help lower our fault current. I would recommend getting NFPA 70E and reading it. Not the most entertaining reading but it can awnser alot for you.
 
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