azezaz123@qwestoffice.net
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Does anybody know the formula for calories per centimeter squared , and the explaination of the formula in fairly understandable terms ??
Robert
- Thread starter azezaz123@qwestoffice.net
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Welcome to the forum.
Annex D of NFPA 70E has some calculation methods as well as IEEE 1584.
Keep in mind that these formulas and calculations are not to be taken lightly and I would recommend that you do not try to preform them yourself. Only an engineer that is well versed in the calculations should do an arc flash analysis.
Chris
Annex D of NFPA 70E has some calculation methods as well as IEEE 1584.
Keep in mind that these formulas and calculations are not to be taken lightly and I would recommend that you do not try to preform them yourself. Only an engineer that is well versed in the calculations should do an arc flash analysis.
Chris
zog
Senior Member
- Location
- Charlotte, NC
There are several different formulas depending on the voltage, equipment configuration, etc.. And there is not a simple way to explain them, in fact the math is more complex than most people can understand.
One if the basic equations is, using the simplified method for LV systems in a cubic box. (I can't even post it right because I don't know how to do subscripts and superscripts in this new format)
EMB = 1038.7DB-1.4738tA[0.0093F2 - 0.0076F + 5.9675]
Where:
EMB = maximum 20 in. cubic box incident energy, cal/cm2
DB = distance from arc electrodes, inches (for distances 18 in. and greater)
tA = arc duration, seconds
F = bolted fault short circuit current, kA (for the range of 16 to 50 kA)
As mentioned, these are not something you should attempt on your own, there are a lot of things to consider and even the pros use high end engineering software to do these.
Was there a specific question you had?
One if the basic equations is, using the simplified method for LV systems in a cubic box. (I can't even post it right because I don't know how to do subscripts and superscripts in this new format)
EMB = 1038.7DB-1.4738tA[0.0093F2 - 0.0076F + 5.9675]
Where:
EMB = maximum 20 in. cubic box incident energy, cal/cm2
DB = distance from arc electrodes, inches (for distances 18 in. and greater)
tA = arc duration, seconds
F = bolted fault short circuit current, kA (for the range of 16 to 50 kA)
As mentioned, these are not something you should attempt on your own, there are a lot of things to consider and even the pros use high end engineering software to do these.
Was there a specific question you had?
zog
Senior Member
- Location
- Charlotte, NC
1.2 cal/cm2 will give exposed skin a second degree brun in 0.1 second, so I don't think your info is corerect. 1.2 cal/cm2 is the basis of everything arc flash related, arc flash boundaries, ATPV ratings for clothing, etc...
I think you're right. Sunlight intensity, that is power, is 1 kw/m^2 and I must have scrambled the conversion.
http://www.onlineconversion.com/
A watt is a joule per second and a calorie, with lower case c, is about 4 joules of energy.
I'll have to do this on paper.
http://en.wikipedia.org/wiki/Dimensional_analysis
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zog
Senior Member
- Location
- Charlotte, NC
skeshesh
Senior Member
- Location
- Los Angeles, Ca
The only way you can convert the 'sunlight' example is to assume an exposure duration.
Sunlight intensity is about 1300 W / meter^2 which is 0.13 W/cm^2. Assuming 1 watt = 0.24 cal/s you can conclude the sunlight can deliver about 0.0312 cal/cm^2 every second.
I still don't really understand what the OP was asking though...
Sunlight intensity is about 1300 W / meter^2 which is 0.13 W/cm^2. Assuming 1 watt = 0.24 cal/s you can conclude the sunlight can deliver about 0.0312 cal/cm^2 every second.
I still don't really understand what the OP was asking though...
You can see the effects of arc flash firsthand with a magnifying glass of any diameter, and the affected damaged area will be small.
The "energy density" of sunlight is much less than 1.2 cal/cm^2 but this can be adjusted by the size of the focused spot. If the spot diameter is 10x less than the magnifier diameter then the energy dumped per square cm is 100x more than that of the sun.
The skin of the "test subject" should absorb and reflect light as well or as poorly as yours does. Exposure time is 0.1 second. It might take a while for the blister to show up.
To test PPE effectiveness you'd need a really large magnifier.
The "energy density" of sunlight is much less than 1.2 cal/cm^2 but this can be adjusted by the size of the focused spot. If the spot diameter is 10x less than the magnifier diameter then the energy dumped per square cm is 100x more than that of the sun.
The skin of the "test subject" should absorb and reflect light as well or as poorly as yours does. Exposure time is 0.1 second. It might take a while for the blister to show up.
To test PPE effectiveness you'd need a really large magnifier.
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zog
Senior Member
- Location
- Charlotte, NC
No, just a test lab like KEMA.
ggunn
PE (Electrical), NABCEP certified
- Location
- Austin, TX, USA
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- Consulting Electrical Engineer - Photovoltaic Systems
I believe that that's the strength of sunlight out in space. At the surface of the earth on a clear day at noon it's about 1000W/m^2. It can be a little higher from time to time.
azezaz123@qwestoffice.net
Member
How does Robert relate to the question in the thread title, shouldn't the title of the thread give a hint to the subject matter?
Roger
K8MHZ
Senior Member
- Occupation
- Electrician
You are correct. This was part of last week's solar installation class.
We use the 'solar constant' which is the measurement of irradiance in space 1AU from the sun. That is 1366 W/m^2.
'Peak sun' is is an estimate of of maximum solar irradiance around solar noon at sea level and is generally accepted to be 1000 W/m^2.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Wow, Robert posted that thread in Feb, and now returns to respond to it. :grin:
K8MHZ
Senior Member
- Occupation
- Electrician
Could be a matter of priorities. I washed my Harley today just in case the rapture comes tonight and the roads have less traffic tomorrow. The bars all should still be open. I'm not sure about gas stations so I got gas, too.
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