Alright, so I am officially a Control's engineer; but we have been task of determining the arc flash rating of our control cabinets, especially those with 480V in them. We also have come up with some way of determining what needs to be worn for 120V and DC, knowing full well that there is no official word.

We have come up with something for 120V because there have been studies done on 120V arcs. These are just studies (mostly from IEEE Xplore), nothing official; but enough for us to understand what is going on and make assumptions, until the 1584 committee comes up with something more detailed.

However, we have not been able to find any detailed studies or models of DC arcs. Does anyone know of any good references?

We already know about this site:
http://www.arcadvisor.com/faq/dc_direct_current_arc.html

Thanks for your help.



Again, I am not looking for any standards because I know they do not exist yet.

I would be careful about what methods you use. I have not seen anyone use or support the method shown in the link that you reference. Maybe someone else has.

I have heard that some tests have shown DC arc flash did not behave exactly as expected.

There will be an "official" verdict in September of this year (2009). The project manager of the IEEE 1584 / NPFA testing group is presenting the results and I'll update everyone here.

Arc Flash Concerns for Communication Battery

I am a communications engineer for a large power company and our battery plants are nominal 48 volts systems but we operate the battery systems at a 54 volt float level. I contend that these battery plants are just below the 50 to 600 volt (AC Low Voltage Standard) levels and should not be subject to Arc Flash regulations. Our safety organization is insistant, however, that since we operate our battery in excess of the 50 volt lower limit that we are subject to arc flash requirements when taking electrical measurements on the batteries during maintenance/testing. They are taking the approach that it is better to error on the conservative side.

You seem to close to this subject and I see where you state that the upcoming DC testing will be presented next month but I was wondering if you would know if the testing will address battery installations such as ours that are right on the edge of the lower limit or if this lower limit will be changed from using the AC Low Voltage standard?

Most any 48 vdc battery bank will float at about 52 to 54 volts. The standards are all about nominal voltage levels, not actual voltage levels. If the committee intended to include 48 vdc banks, I think they would have set the limit at 48 instead of 50 vdc.

The "official verdict" I spoke of earlier regarding DC did not happen. Only a paper that was more of historical perspective of DC was presented.

We had a testing update during the 1584 meeting a few weeks ago and sad to say there is not much new information to report. As I have mentioned in the past, as soon as I hear of any new tests, data, reearch etc. I will post it here for everyone to see.

DOE handbook 1092-2009 Info

DC information in the attached pages.
This is the extract from DOE-HDBK-1092-2009 (electrical safety).
I cannot load entire document as the file size exceeds the limit.
If I find the source, I can add it later.

DOE Handbook 1092-2009 Draft source

[url="http://www.lanl.gov/safety/electrical/docs/09_doe_electrical_safety_handbook_rd.pdf"]http://www.lanl.gov/safety/electrical/docs/09_doe_electrical_safety_handbook_rd.pdf[/url]

Jim,

I am assuming the paper is [url="http://www.ieee-pcic.org/Conferences/2009_Anaheim/technical.html"]DC Arc Models and Incident Energy Calculations[/url].

I managed to get my hands on the paper here, finally, and while I will agree with you that the paper was definitely a historical perspective of arc flash analysis (many of the historic equation are not derived from DC systems). I still believe the method and logic presented in this paper is currently the best DC analysis out there. It offers a very conservative estimate in analyzing DC systems.

The biggest problem we have with it is the method appears to assumes a battery is an infinite source. We have 28V battery racks, with a fault current of 4800A, that are rated Category 3's. This will make it very hard to justify to our AHJ, who is asking for it.

We are currently trying to find a way to factor in the short circuit curve of the battery, into the equation; but if not I would argue that the model described in this paper is currently the best model I have seen to rate DC systems. Although, it is not standard, so use at your own risk.



Does anyone else think we are over thinking such a low voltage system?

You have the correct paper. We are someday suppose to receive detailed test results to develop a better DC model but so far nothing much seems to be happening. I am hopeful we will be able to include such a model in the next version of IEEE 1584.