necnotevenclose
Senior Member
Has anyone been required to do an arch flash study based on a local AHJ?
ARC Flash Study
- Thread starter necnotevenclose
- Start date
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zog
Senior Member
- Location
- Charlotte, NC
We have done many in Michigan and Ohio, seems the EI's are requireing it be done in many areas
ron
Senior Member
- Location
- New York, 40.7514,-73.9925
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?
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.
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.
ron
Senior Member
- Location
- New York, 40.7514,-73.9925
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.
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.
mayanees
Senior Member
- Location
- Westminster, MD
- Occupation
- Electrical Engineer and Master Electrician
..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
..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
Senior Member
- Location
- Charlotte, NC
Mr Bill, you need to read the NFPA 70E and or IEEE 1584 for some guideance on these calculations.
kingpb
Senior Member
- Location
- SE USA as far as you can go
- Occupation
- Engineer, Registered
I have the IEEE 1584 Excel Spreadsheet if anyone would liketo have it.
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
zog said:
under what authority would an EI have to require such a thing? there is no code requirement involved.
zog
Senior Member
- Location
- Charlotte, NC
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.
kingpb
Senior Member
- Location
- SE USA as far as you can go
- Occupation
- Engineer, Registered
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.
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.
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
zog said:
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 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.
necnotevenclose
Senior Member
Would an ARC flash study include an entire system from a 2000A 480V switchboard down to say a 208V 125A loadcenter?
ron
Senior Member
- Location
- New York, 40.7514,-73.9925
necnotevenclose,
It would be anything that might be worked on or near while energized.
It would be anything that might be worked on or near while energized.
weressl
Esteemed Member
necnotevenclose said:
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.
robh
Member
- Location
- Oregon..Not Orygone
"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.
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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