Arc flash calculations assume the door is open. This arc flash video shows why. Although not an extreme amount of short circuit current for this test, it is enough to create enough blast pressure from the arc flash and blow the door open. Do the doors blow open for every case? No. But it is difficult (impossible?) to determine if it will so to be conservative, it is assumed the doors are open. This video was from arc flash testing by Jim Phillips for IEEE 1584 to determine the behavior of the arc based on the electrode orientation.
One of the questions that I frequently receive about arc flashes– do the doors offer any type of protection from an arc flash? And the short answer is no, but probably the more correct answer is we’re really not sure. It’s just hard to tell. It’s unpredictable. And unless you have equipment that’s designed for the doors to remain closed, like arc resistance switch gear and motor control censors, there’s just no way to know for sure.
So, to be conservative, the way we approach this is that you just assume that the doors are open. And I have a couple of videos that I took in the lab last year that I wanted to show you to illustrate this. The first video is a 400 amp bus plug, and the doors open. And we set this up. It’s at 600 volts with 23,000 amps of short circuit current. And, so, let’s see what happens first with the doors open.
600 volts, test 21. Went inside the room. Under the door.
That was quite an impressive event. I sure wouldn’t want to be standing in front of it. But then we took the same 400 amp bus plug. And this time we had the doors closed, and basically repeated the test. And watch what happens in this case.
OK, let’s go. 600 volts. And the door does not offer protection.
Based on that last comment, I have a pretty keen perception of the obvious. The doors don’t offer protection, at least in that case. And that’s the way that it is quite often.
So, we really just don’t have any way to know for sure whether or not the doors will offer protection or not. So, the safe way to go, and this is the interpretation that’s used in the industry, is you just base this on the doors being opened. They’re not going to offer any kind of protection. 23,000 amps. That’s a pretty respectable amount of short circuit current. And that was enough to blow the doors open.