Arc Flash Studies and Electrical Diagrams

One line diagrams that are used as part of an arc flash study must be up to date.  NFPA 70E 120.1 Verification of an Electrically Safe Work Condition, requires checking up-to-date drawings, diagrams and tags when verifying an electrically safe work condition.  In addition, when performing an arc flash study/risk assessment, an up-to-date one line drawing is the primary document that defines the system under study.

Jim Phillips discusses how, unless a study was performed, most companies do not have up-to-date electrical drawings.  This is one of the many subjects discussed in Jim’s Electrical Safety and Arc Flash Training programs.


Video Transcript

How up to date are your one-lines? That that’s a question a lot of people wrestle with, and they’re really important when it comes to electrical safety.

One of the reasons is NFPA 70e120.1 for verification of an electrically safe work condition– says that you’re supposed to check applicable “up to date”– and that’s the key thing, up to date– drawings, and diagrams, and identification tags. You also need to have an up to date one-line– or single line, as some call them– when you’re performing an arc flash study. Basically, it defines the road map of what your system looks like.

So I asked this question at the arc flash forum–– do you or your clients, if you happen to be a consultant– you have drawings or diagrams that are up to date, thinking in terms of one-lines and single lines? And the answers were kind of as expected. 25% of the people said yes. That’s it. Only 25% percent of the people. 51% said that no, they need to be updated.

And you may be looking at this thinking, well, wait a minute, Jim. 25 and 51– that’s not exactly 100%. What are we missing here? Well, I had a little fun with this, and I also asked the question, drawings? I’m not even sure they exist. That was 24% of the people. So the bottom line in most cases– when you’re performing an arc flash study, or you’re going to verify an electrically safe work condition, there is going to be some work that’s going to need to be done to bring diagrams and drawings up to date.

I know back in my past, one of the places that I used to work– this was actually back in the late 1970s– they had drawings that dated all the way back to the early 1900s. It was a very, very old industrial facility. And that’s the case. Sometimes if you happen to find a one-line drawing, or you ask a client, do have a one-line drawing? They’ll say, oh, yeah. We do. And then you look at it and you find out, well, it’s 20, 30 years old. Is that up to date? I really doubt it.

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