I'm pushing through the brilliant book "Industrial Power System Grounding Design Handbook" by Dunki-Jacobs and Co. In it, the authors indicate that copper is endothermic (absorbs energy when converting from solid to liquid) and aluminum is exothermic (releases energy when converting from solid to liquid).

They claim that due to these differences equipment with internal aluminum construction has a much greater potential for destructive energy release during an arc fault vs. copper construction. Does anyone account for this difference in their analysis of systems? The program I use for arc flash evaluation does not give me an option for copper vs. aluminum windings in the distribution transformers so I can't compare & contrast material types for IE levels. For panelboards I do have the ability to adjust for material type but it doesn't appear to make a difference for IE levels based on a quick sample study I just did.

Thoughts? Is material type a consideration that needs to be addressed? I believe the answer is no but wanted the groups opinion.

Thanks,
Brian

There is a difference in terms of the incident energy depending on the material of the ELECTRODES (where the arc roots are located) depending on if it is steel, copper, or aluminum. Some testing has been done for aluminum and copper. But as of right now it is not included as a factor in any incident energy calculations. So maybe IEEE 1584-2017 o 2018 or whenever it gets finalized will have this additional fudge factor but right now it's a scientific curiosity.

Thanks Paul. For what it is worth here is the response from the calculation software company:

"Thank you for your email inquiry.

Within the IEEE 1584 Standard, it mentions looking at various tests with copper, aluminium, and other materials, where it states that insignificant changes affect the results. These test results are then used in the standard's arcing current calculations to derive the IE levels and AF boundary.

The selected conductor material will have an affect on the impedances in turn affecting the short circuit values. This potentially affects the arcing current and arcing time of the trip device and the IE levels, but suspect insignificantly (unless a huge difference is encountered with the conductor - length and other parameters). Hope this information is helpful."

Similar response to what you had said Paul. Wait and see if the future IEEE 1584 addresses this differential.

ArcPro 2.01 has choices for stainless steel or copper electrodes.

The presumption is incorrect. Both aluminum and copper require the addition of heat to melt.
http://www.engineeringtoolbox.com/fusio ... _1266.html

Aluminum does have a tendency to oxidize and if ground to a dust can be explosive. I would presume that if one sprayed molten aluminum in air one would give off additional energy from oxidation. Perhaps this is what the author was alluding to.

If you take it backwards, if the change from Solid to liquid aluminum was exothermic, you could never get the aluminum to solidify in the first place. As it started to "freeze" it would get hotter and hotter, which of course stops it from freezing.

Or to look at it another way, the structure of the atoms would have to get more and more ordered, and their speed slower, as they got hotter, not less ordered and faster.

I have done quite a bit of work on this in the late 1990's. There are several factors. ArcPro's calcs are based on my work (FR ASTM clothing testing) and additional work done by Kinectrics. Basically Copper puts out a little less energy to a worker in an open air arc (we believed due to reabsorption of photons by the dust and smoke). We chose Stainless Steel for testing because it products less smoke (for the test lab) and more energy for the garment.

AL is on average higher than copper but has more variation due to even more ALOxide smoke. This all changes with ejected arcs since you have more pure energy from the roots but workers rarely will see the roots at the skin or garment surface.

In real life there will be little difference if you are wearing AR garments. AL MIGHT ignite a non-FR garment a little easier but the molten metal often is MUCH cooler by the time it reaches most of the workers body.

I would doubt you would see enough difference to make it necessary to correct for electrode type and they is likely why IEEE 1584 didn't require it in the models.

Hugh Hoagland
e-Hazard.com
ArcWear.com